What medical issues or procedures can cause denied medicals? Are there a lot of things that can cause a denied medical? Can fairly routine procedures be grounds for denial? (Please don't hate me for having 2 questions in one!)

Its really no big secret, the FAA publishes their full guide for AME's and you can read it if you like (all 514 pages...) and generally speaking it lists a lot of the disqualifying factors. They offer various guides as well, all of which are public.
If you are worried that something relating to you personally is grounds for denial you can always reach out to an organization like AOPA for assistance.
Routine Procedure is a fairly broad term and an answer cant really be provided since this can be highly case by case depending on what the procedure is.


What is the cause of unusually strong wake turbulence from the 757? The Boeing 757 (at least in the US) is in a special class of its own with respect to air traffic control wake turbulence advisories and separation. This is apparently due to it producing stronger wake vortices than would be expected from an aircraft of similar size and weight. What about the 757's design causes these strong vortices? What led to the decision to treat it differently than similar aircraft?

My understanding, primarily based on this archived NASA document (also linked to on the B757 Wikipedia article), is that there were several issues leading to the decision to make the 757 a special case.

First, there were some notable accidents where witnesses seemed to indicate the cause was 757 wake turbulence.

Cessna Citation - December 18, 1992 - Billings, Montana

  Witnesses reported that the airplane suddenly and rapidly rolled left and then contacted the ground while in a near-vertical dive. Recorded ATC radar data showed that, at the point of upset, the Citation was about 2.8 nmi behind a Boeing 757 and on a flight path that was about 300 ft below the flight path of the 757.

IAI Westwind - December 15, 1993 - Santa Ana, California

  witnesses reported that the airplane rolled abruptly and that the onset of the event was sudden. The Westwind was about 2.1 nmi behind a Boeing 757 and on a flight path that was about 400 ft below the flight path of the 757.

Additional accidents were noted with a Cessna 182, MD-88, and a Boeing 737.

Second, there were some controversial NOAA flyby tests which showed:

  for a peculiar set of weather conditions that lasted about 0.5 hour, the vortex velocity of the 757 was approximately 50 percent higher than that of the 767 at similar vortex ages (younger than 60 sec) measured in less favorable weather conditions. However, the results also showed that overall the wake of the 757 decayed faster than that of the 767; in fact, the wake behaved as would be expected for an aircraft of the size and weight of the 757.

Third, they felt the slower approach speed of the 757 (vs. similar aircraft) made it more likely that trailing aircraft would inadvertently close the separation gap during approach.

Ultimately, I believe the correct answer to your question is actually that there is nothing particularly special about the B757 in regards to wake turbulence. This Air&Space Magazine Article indicates that

  Boeing maintains that there is nothing about the wing design that would cause wake turbulence.

and

  "The wake from the 757 is no stronger or weaker than you would predict from the weight, span, and speed of the airplane," agrees NASA's David Hinton, who has taken wake measurements at airports around the country and is principal investigator of NASA's NextGen Airportal Project.

The decision to put the 757 in its own category was controversial at the time and not based on particularly strong evidence. It was done out of precaution due to anecdotal evidence and possibly flawed test results. On the other hand, you could argue that ATC erring on the side of caution is best if there is any doubt. To be fair, a 757 is on the larger side of the small category.


Can aircraft stall at low speed during final landing? Is it possible for an aircraft to stall when it turns multiple times before landing and its airspeed is below 200mph? And if it does, is there any way to recover at such low height and speed? I always get nervous looking out the window and feeling that 1.5g in my seat during landing.

When you learn to fly one of the first things that you learn is that recovering from a stall at low altitude is rarely successful. So we go up to at least 1,500 Above Ground Level (I like to go even higher) and we practice putting the airplane into a position just before it stalls—the stall warning light goes on and the wing begins to buffet. Then we use appropriate power, ailerons, and rudder to recover from the stall. Every pilot is tested on this before they receive their pilot’s license. Commercial pilots and air transport pilots are tested again with higher standards than private pilots. The idea is that you know the conditions that result in stalls and avoid getting into that situation. If for some reason you do stall the airplane, your training should kick in and you should be able to recover.

Unfortunately, many general aviation pilots get distracted on final approach and there are frequent stall-spin accidents in light airplanes. They are extremely rare in the airlines. The only one that comes to mind is the Colgan Air accident in 2009 where the plane iced up and the pilot flying ignored the stall warnings and pulled up on the stick instead of pushing the nose down and adding power.

We are taught that a stall can occur at any airspeed and any pitch if the airplane exceeds the critical angle of attack. There are lots of ways you can do that but the two most common are banking and icing up the wing. The Colgan Air crash is an example of the later. When the wings are iced up they do not provide as much lift as when they are clean. In order to keep the plane level you need to increase the pitch. This increases the angle of attack and at some point the wing exceeds the critical angle of attack and the plane stalls.

I am not aware of any recent airline accidents related to stalls while banking but there are plenty in light aircraft. An unfortunate series of events resulted in a stall spin accident in a Cirrus at Houston’s Hobby airport in 2016.

In the example you gave in your post of a 1.5 g load factor the stall speed increase is only going to be a few percent. So if you were in a Boeing 737 with a stall speed in the landing configuration of ~125 knots, the stall speed in the turn would be a few percent more—say 130 knots. The pilots know this information and will keep the angle of bank and airspeed within limits.

One of the maneuvers that we must master to get our Commercial license is steep turns of 50°. My Cherokee has a stall speed of 55 MPH in the approach configuration. The stall speed at a 50° bank angle is approximately 1.28 times 55 = 70 MPH. For me to successfully do a steep turn, I need to enter the maneuver at an airspeed of greater than 70 MPH.

Another maneuver that we must master is an accelerated stall. In this case we start out at our approach airspeed (in my Cherokee it is 80 MPH) and we bank to 45° and then pull up on the yoke. As you can guess from the discussion above, the airplane almost immediately stalls and then we recover from the stall. The reason we practice this maneuver is so that we don’t do this when coming in for a landing.

What causes pilots trouble is forgetting that your stall speed increases dramatically in a steep turn. Suppose you are turning to line up with the runway and you underestimate the wind and it blows you past the runway centerline. The natural reaction would be to steepen the turn. But when you steepen the turn you change the vertical component of lift so you start to sink toward the ground. If you pull up to get away from the ground you lose airspeed as well. So now you’ve increased the angle of attack past the critical angle of attack. The airplane stalls and if you weren’t coordinated with the rudder (which is often the case) the airplane enters a spin. This close to the ground they are rarely recoverable.

Stalls occur because the airplane exceeds the critical angle of attack. In most normal flying the angle of attack is directly related to the pitch and bank angles and the airspeed. We are taught how to avoid stalls in our primary training and when we get our refresher training every two years. We still manage to mess it up. Airline pilots receive much more training than we do and it is reflected in the accident statistics.


What is the maximum wind speed a Boeing 737-800 can deal with during takeoff and landing? I'd like to know how safe the Boeing 737-800 is during takeoff and landing when it's windy. What are the maximum wind speeds for cases of tail, head and cross winds?

EDIT

I've found this resource http://www.b737.org.uk/limitations.htm#Wind_Limits, but I'm quite unable to understand the data:

According to the table (which only shows x-wind data), the max wind speed depends on the so called "braking action", but I don't know what exactly is nor what it depends on.

EDIT 2

The same resource points out the max tailwind speed, as well as other info:

As your source shows, the maximum tail wind is fixed and fairly simple.

Getting slightly more complex, there is technically no maximum headwind I'm aware of, although most airports will close when the wind gets much above 50 knots, and even with the wind coming almost straight down the runway, you still get some crosswind component, which factors in. Expect to see many pilots divert in winds much above 40 knots even if the airport is open, especially if gusting to above 50.

Crosswinds are a little different as they depend on the braking action - basically how grippy the runway is. Simplified, you can think of it as a scale from dry weather, through slightly and very wet, then slush and ice. The grippier the runway, the more the tyres will grip and the higher crosswind the aircraft can deal with. The higher numbers in the chart you show are for a dry runway (good on your chart) the lower numbers for wet or icy (poor on your chart) runways.

Although it's written in terms of 'braking action', it's really a measure of grippiness, and it's important both when braking, but also for the ability of the tyres to prevent the aircraft sliding laterally off the runway. This job doesn't solely come down to the tyres, but they're part of it. This is also a large part of the reason why landings and takeoff have different maximum crosswinds on some aircraft.


If all fighter jets become stealthy, how will they fight each other in the future? In dogfights? I came across this question on dogfight-capable fighter jets still being made. If all aircraft become so stealthy, how will they fight each other? Only in dogfights, I presume. Or am I wrong?

Table of contents

  Future focii
  Short answer - Important: stealth, sensors (radar & IR), data fusion, networking, long-range weapons. Unimportant: dogfighting with guns.
  Future counter-detection and counter-measures - Important: RF and IR stealth, lasers, hard-kill defenses
  How will stealth fighters fight each other? - including THE MOST IMPORTANT LESSON
  Busting myths

  Myth: Stealth aircraft can't use radars / radars reveal your location - LPI radar
  Myth: IR sensors render stealth obsolete - IR range is short; shorter than radar range against nonstealthy a/c, but greater than radar range against stealthy a/c
  Myth: US lags behind Russia/Europe in IR tech - US had less need (better radars); US has very good IR tech
  Myth: Stealth makes you invisible to radar  - very hard to see, not invisible
  Myth: Stealth is obsolete / a hoax / just marketing - vastly reduced detection range; more efficient jamming; dictate engagements
  Myth: WWII/low-freq radars make stealth obsolete / an F-117 was shot down with this one simple trick - Low-freq radars have limited use; F-117 story is untrue.
  Myth: most combat is WVR dogfighting - not since the 1960s
  Myth: Guns are primary weapons. F-4's were massacred by obsolete MiG-21s in Vietnam because they didn't have guns.

  F-4 guns myth - the F-4s did just fine
  Welcome to the BVR missile era - where missiles take all the credit, and you usually don't see your enemy

  Resources - for modern air combat
  Glossary

As aircraft become stealthier, we'll rely more on the following:

Non-radio sensing

IR search and track (IRST)
Optical sensing
(EO/IR are/can be combined into essentially an EO/IR telescope. Future designs will use multiple bands (MWIR, SWIR, color HDTV), have wider fields of view
Mid-future: laser tracking and targeting.
High-powered lasers (100s of kW) for fighters won't debut for decades, but in the meantime they could obtain very high quality bearing, range, speed, and altitude information.

Networking and data fusion

Highly integrated aircraft sensors
Off-board targeting
Eg, a very stealthy sensor platform feeding targeting info to less stealthy (even non-stealthy) launch platforms.

Advanced radars

Multi-band or broadband radars (integrated mid/high-frequency capabilities)
More powerful AESA radars
Better processing
Multi-static arrays to detect side-aspect radar returns.
Side-looking radars.
Again, VLO a/c are not equally stealthy in all directions. They are least detectable from the front aspect.
For instance, the F-22 was to be upgraded with cheek-mounted, side-looking radars, but these were cancelled to reduce cost.

Even better stealth

Short answer

Detection ranges will shrink (against other LO fighters). IR sensors may become the primary means of detection. Fighters may cruise at low subsonic speeds to delay detection.

Radar will still remain the primary sensor for years to come (at least 2 decades, the minimum time for adversaries to field large numbers of LO a/c).

Stealth remains essential.

DATA FUSION and NETWORKING become hugely important; large forces must fight as seamless units. Remote targeting will become more common. Very, very stealthy sensors (eg, F-22 successor) may pass targeting info to less stealthy shooters (eg, F-22, F-35, F-15, missile truck with VLRAAMs)

Future AAMs will feature datalinks and multimode seekers (eg, IR, RF, and laser), improving counter-measure resistance. Many AAMs already have datalinks---shooter guides the missile until the missile's own seeker acquires the target. Advanced propulsion systems debut (multi-pulse motors, ducted-rocket/ramrockets, scramjets), yielding longer range, higher speed, imrpoved kinematics.

Defenses will improve, requiring deeper magazines (smaller weapons and/or larger internal payload bays).

Space, weight, power, and cooling requirements go up. Aircraft grow larger.

Dogfighting will remain rare. Short-range, maneuvering combat will remain unsurvivable with the advent of reliable, high-performance, high Pk, HOBS missiles and helmet-mounted cueing systems. Also, lasers don't miss. (See Myth: guns below.)

5th gen fighters (F-22, F-35) will thoroughly dominate over 4th gen fighters (F-15, Su-35, Typhoon).

Regarding counter-detection and counter-measures

Fighters will better hide their RF and IR signature. See: engine exhaust troughs on F-117, B-2, YF-23, and 6th gen fighter concepts. See: AETD, ADVENT, and F135 upgrades. Tails may disappear.

EW (eg, jamming) will remain important (See: Myth: Stealth a/c can't use radar).

DIRCM (directed IR countermeasures, an IR laser to jam/kill missile IR seekers) will protect fighters and bombers. Already slated for the F-35.

Hard-kill missile defenses will debut (likely small anti-missile missiles in near-term; anti-missile lasers 20+ years hence). Today, we rely primarily on soft-kill defenses, like jamming and decoys.

Answering the question: how will stealth fighters fight each other?

With better sensors and better stealth.

With mid- to long-range missile shots, but mid-range detection (eg, networked, off-board targeting).

With more lethal weapons (faster/short fight time, improved terminal kinematics, less spoofable sensors).

And with better defenses.

In other words, not unimaginably different from how the F-22 sometimes fights today -- a variation on 5th gen combat. Why? [See note.]

Because stealth hasn't changed the most critical component of aerial combat since WWI: SA -- situational awareness -- obtain SA and deny it to your enemy.

THIS IS BY FAR THE MOST IMPORTANT LESSON IN THIS ENTIRE POST. If you learn nothing else, learn this: SA and OODA.

Then do exactly this:

Watch F-18/22/35 pilot and TOPGUN instructor LtCol Chip Berke discuss 5th gen combat.
Go to the resources at the bottom of this post.

Read CSBA's Trends in Air to Air Combat: Implications for Future Air Superiority (or listen to the 1hr presentation) to see how modern air combat is actually fought.
Read The Radar Game to find out why SA (and stealth) is so important.
Read the Gulf War Air Power Survey. Short, concentrated glimpse into modern air wars.

Learn to fly a fighter.

Seriously. Go pick up FSX or DCS and learn. There's a vibrant community to help you out if you get stuck. (You only fly the F-16 in FSX, but it has a dynamic campaign. DCS has far more pilotable a/c. Both are VERY realistic.)
You'll quickly learn that flying the plane takes a lot more effort and is a lot harder than you imagine. You'll spend much of your time flying the plane (or crashing), not actually fighting... which makes sense because it's the same in real life. (The F-14 has two crew for a reason.) You'll quickly appreciate the luxuries of modern conveniences (like auto-trim). "Data-fusion" and "networking" will start to mean something. SA will become the difference between life and respawn.
You'll also learn that dogfighting is very dangerous. You'll rely more on your AMRAAMs than you guns (once you learn to use the radar ;)). You'll resent the Russian IR AAMs, which don't show up on your radar warning receiver. You'll learn the F-16 is not nearly as agile at medium altitude as headlines led you to believe... especially not when loaded with weapons, fuel, and sensors.

To give you a snippet of The Radar Game:

In most victories, the target isn't aware they're being shot at. SA was determinant.
The most successful aces don't engage in gladiatorial 1v1 dogfights -- more like hit-n-run.
Points 1 and 2 apply from WWI to the present day.
Reaction times are measured in seconds, a function of detection range and closing speed. Radar increases your reaction time; stealth decreases your enemy's reaction time.

[Note well: 5th gen platforms already operate differently from their predecessors ("speed is life")].

[Note: it goes w/o saying my prognostications are opinions. Although I'm confident in my predictions -- which are vague but reflect longstanding trends and realistic S&T developments -- I don't pretend certainty.]

[Note: timeframe is near- to mid-future.]

Addressing myths

Myth: Stealth aircraft can't use radars / turning on radars instantly reveals your location

Low-probability of intercept functionality allow you to use your radar without being detected you. Principals of operation include using wider-frequency bandwidth (wideband), frequency hopping, using a frequency-modulated continuous-wave signal, using only the minimum power required for the task, and pulse compression. Wiki has a good summary. AESA radars are particularly suitable because of their thin, pencil-like beams and minimal side-lobes.

Here's a Naval Postgraduate School thesis on the detection and jamming of LPI radars.

This is similar to how LO a/c communicate without being detected. The F-35 is equipped with MADL - multifunction advanced datalink - a stealthy, secure, minimum power, high data rate, line of sight comms system.

Myth: IR sensors render stealth obsolete

Bodies heat up when moving through air.

Vid: F-16 seen through an F-35's EODAS

Vid: F-15E in IR.

IR sensors do not see as far as radar (contrary to other answers here).

Against 4th gen fighters (non-stealthy platforms):

IRST detection range is typically measured in low-dozens of miles.
The F-15's radar ranges out to 100 nmi
The F-22's radar ranges out to 150 nmi
The E-3 Sentry's radar ranges out to 400 nmi

For reference, the F-14's optical (not IR) system could ID and track bombers out to 50 nmi. Perhaps 15-25 nmi for fighters. (Some IR bands are less readily  absorbed by the air than visible light.)

The PIRATE IRST may detect a VLO fighter (with RF and some IR reduction) from these ranges (CSBA):

Altitude  | Mach | Stag temp | Ambient | Contrast | Detection range
==========|======|===========|=========|==========|================
45,000 ft | 1.8  |  85 C     | -56 C   | 141 K    | 150 nmi
45,000 ft | 0.8  | -28 C     | -56 C   |  28 K    |  48 nmi
45,000 ft | 0.5  | -45 C     | -56 C   |  17 K    |

(150 nmi figure assumes no afterburner, ie supercruise.)

While IR is harder than radar to jam at long range, it can't estimate target range as easily.

Myth: US lags behind Russia/Europe in IR tech

Again, IR sensors don't see as far as radar, but they are harder to jam from long range. Historically, NATO fielded better radars and jammers than the Soviets, who therefore couldn't rely as heavily on their radars. So the Russians added IRST capabilities to augment their radars.

Remember also that the US flies dozens of AWACS that usually detect enemy a/c long before even an F-15's radar. So IRST wasn't as critical for US fighters.

The F-22 has a space reservation for IR sensors, but that upgrade was cut to reduce costs.

The F-14 received an EOST relatively early because its main targets were large, Soviet bombers, which are easier to detect.

The US eventually added IRST to late-block F-16's, Super Hornets, and of course the F-35, which fields the most complete IR sensor suite of any fighter. The F-35 has a stealthy, built-in IRST that doubles as a targeting pod. (Demo.) Its DAS also allows pilots to see in a complete sphere (4 pi steradian) around the a/c, even through the floor and headrest (no blindspots); its primary function is missile approach and warning.

The F-35 is an important example here because it'll soon comprise the backbone of NATO aviation for decades. Some 3,400 F-35s are slated for production, more than all F-15s, Super Hornets, Rafales, Gripens, Eurofighters, and Su-27s produced to date combined.

(Btw, if you're skeptical about the F-35 -- kinematics (speed, dogfighting v. F-16), range, stealth, weapons (gun), software, cost -- I'll direct you to these two..comments on kinematics, this compendium, and this community. (To start, a fully loaded F-35 with 5k lbs weapons accelerates like a clean F-16 and points its nose like a Hornet.) If you're still skeptical, I can start another 30,000 character post.)

Myth: Stealth makes you invisible to radar

Not quite.

Stealth vastly reduces your RCS, but does not completely erase it.

VLO a/c are much, much harder to detect and track. Active radar detection range goes with RCS1/4. So a 10x reduction in RCS roughly halves detection range. [See radar equation.]

For example, an F-22 or F-35 has an RCS of 0.0001 m2. A clean [unarmed] F-16 has an X-band RCS of about 2 m2. The F-22/35 will be detected at 12-22x shorter ranges than the F-15/16---effectively under 5-10 miles when using a fighter-class radar. That's almost close enough to see [see note] and certainly within IRST range.

Platform | RCS m^2 | 1/range | Detection range
=========|=========|=========|==================
 F-15    | 25      |  1.0    | 100.
Su-27    | 15      |  1.1    |  88.
 F-16C   |  1.2    |  2.1    |  47.
 F-18    |  1      |  2.2    |  45.
Rafale   |  1      |  2.2    |  45.
Typhoon  |   .5    |  2.6    |  38.
Bird     |   .01   |  7.1    |  14.
Insect   |   .001  | 13      |   8.0
 F-22    |   .0001 | 22      |   4.5
 F-35    |   .0001 | 22      |   4.5

(RCS values are ballpark figures for clean aircraft. External stores greatly increase RCS. A typical F-16 loadout for permissive environments (eg, ISIS, COIN) includes 2x 370 gal fuel tanks, 2x 2000 lb JDAMs (or equivalent), 2x AMRAAMs, 1x Sniper targeting pod. 2x AMRAAMs, 2x AIM-9s, a nav pod (eg LANTIRN), and an ECM pod may be added in more challenging environments. Like this. Not like this. Exception: F-22 and F-35, which carry their stores internally in high threat environments.)

[Note that visual range is theoretically up to 20 miles. But in 99.9% of real life cases it's <5 miles. Often just 2-4 miles.]

Note that once loaded with fuel and weapons, the F-16 and F-15 have much larger RCS values, so will be detected from even further out.

Also, while we no longer use large faceted designs (see: F-117) thanks to modern computing, we still shape our a/c to direct radar energy in certain directions away from the transmitter -- mostly to the sides and above -- in narrow lobes or "spikes."

Illustration (video). Skunkworks engineer discusses designing stealth. Listen closely.
Screencap:

Placeholder: once detect radar transmitter, stay out of detection range. Because detection range is so short, you have a lot more elbow room than non-stealthy fighters.

No, you're not invisible to radar, but operationally, it's much easier to remain undetected.

Placeholder: B-2 spike management. mission planning.

Myth: Stealth is obsolete / stealth is a hoax / stealth is marketing

LO remains relevant (and very useful) for the same reason armor didn't become obsolete when antitank guided missiles were fielded.

LO also makes jamming far more efficient. Jamming basically hides your aircraft's 25 m2 RCS. If your RCS is only 0.0001 m2, it takes far less power to hide yourself, and your jamming will work at far greater range. Primer: how jamming works.

LO technologies drastically reduce detection ranges and warning times. Sensors that work well against stealthy aircraft would work far better against non-stealthy aircraft.

What's the alternative to stealth? No stealth? Make our aircraft easier to detect and track?

All future combat a/c designs must consider signature reduction going forward---at the very least some signature reduction, if not outright VLO designs---camouflaged tanks are always more desirable than this (or this):

Myth: WWII radars / low-frequency radars make stealth obsolete / an F-117 was shot down by an 1960s radar with simple modifications

First, the F-117 story is untrue. The Serbs claimed they made simple modifications to their old Soviet radars, allowing them to easily spot the F-117s. But Zoltán Dani, the Serbian commander who shot down the F-117 in Kosovo, later admitted on national TV that he never modified the radars, merely used the lowest frequency setting. He explained that he fabricated his story for propaganda. Others alleged he did it to take [more] credit for shooting down the F-117.

Also, NATO jamming support was unavailable the night the F-117 was shot down. Dani was aware, so he turned his radars on a third time without relocating, which allowed him to obtain the fateful radar lock.

But more importantly (and accurately) the F-117 was shot down because of lazy mission planning by the US. The F-117 flew the same route night after night at roughly the same hours. So the Serbs moved their radars directly beneath the anticipated flight path. After a number of attempts were made over several nights, they finally got a lock at just 8 mi (13 km) when the bomb bay doors opened. The F-117 doesn't have a radar warning receiver---the pilot never knew he was directly overflying a SAM radar site (doable, but still ill-advised for any stealth fighter). He only ejected because he visually spotted the missile heading for him.

People forget the F-117 is an old design. It entered service in 1983, just five years after the F-16 and nine years after the F-14. Back then, we didn't know how to integrate radars and other apertures into the skin without compromising its low signature.

To be clear, a kill is a kill, and Dani deserves credit. People also forget that the Serbian forces were motivated, competent, and well-trained---measurably more so than Saddam's air defenses. The Serbs performed much better than the Iraqis and learned much from the lessons of Desert Storm.

The F-117 was only shot down once in its entire career, despite regularly flying into some of the most heavily defended airspace in the world, a feat no other platform could perform without massive support (expensive!)...

...or massive losses (save the B-2, F-22, F-35). Stealth alone allowed the F-117 to survive. Even F-15s and Su-35s would have been shot down in droves if we sent them on the same missions alone. (Image source)

Second, low-frequency radars have several drawbacks:

extremely large and power hungry, suitable only for ground-based platforms, not fighters. Some are vehicle-based, but as so large, they're only semi-mobile
require large apertures to function, owing to their long wavelengths
easiest to spoof
easy to detect from long range
detection range is grossly over-advertised
resolution is terrible (on the order of kilometers), making them unsuitable for targeting.
the most straightforward countermeasure to low-freq radars is to make aircraft larger. So VLO bombers (large a/c) are far less detectable by low-freq radars

(Principal: long wavelengths approach the feature size on aircraft, like tails, so shaping is less effective in redirecting radar returns)

all the above make them easy targets for long-range weapons like cruise missiles.
for all the above reasons, they're usually used as early warning radars or to cue higher-frequency radars.

High frequency radars are suitable for targeting, are more jam resistant, and are smaller/lighter. That's why fighters are optimised for stealth at higher frequencies.

Analogy: you can hear a fly buzzing around your room somewhere (detection), but you must see it to swat it (higher resolution sensor for weapons quality track). You can use your ears to cue your eyes, but you'll never hit it with your eyes closed.

(Lo-freq on left, hi-freq on right. SMSgt Mac, elementsofpower.blogspot.com)

Myth: WVR combat / dogfighting is the primary arena of aerial combat

First, WVR combat =/= dogfighting =/= guns.

Second...

Myth: Guns are the primary weapons of aerial combat. F-4's were massacred by obsolete MiG-21s in Vietnam because they didn't have guns.

Common F-4 myth

When Vietnam started, USAF and Navy F-4's claimed just a 2:1 kill/loss ratio. Here commentators often blamed malfunctioning missiles and lack of a gun.

So the USAF added a gun to the F-4, but their K/L remained at 2:1.

In contrast, the Navy began a new program to better train pilots how to use their missiles. They also trained the maintenance crews how to properly handle and maintain their missiles. They did not add a gun.

By war's end, the "sluggish" Navy F-4's claimed a 12:1 K/L ratio against its more maneuverable adversaries like the "agile" MiG-21.

That training program? It became TOPGUN. (Source.)

Welcome to the BVR missile era

The last fighter v. fighter guns kill was in 1989, an Iranian F-4E shooting down an Iraqi Su-22 (CSBA). The F-35's gun is largely for air to ground.

The vast majority of kills over the last 40 years were achieved with missiles:

(Global, fixed-wing v fixed wing. "Other" includes things like CFIT and flying into your own drop tanks. CSBA. See pg 24, pg 36 of 76). Annotation.

In the 1960s, guns still dominated. Most gun kills were achieved by Israelis; they used guns exclusively because no one would sell them missiles.

However, by the 1970s, missiles accounted for more kills than guns.

Even in Vietnam, the AIM-7 Sparrow missile accounted for more kills than any other weapon.

North Vietnam also favored missiles for the balance of its air to air kills, especially as the war progressed.

By Desert Storm, most shots were fired from BVR. Few air to air engagements required any significant maneuvering at all. Only two air to air guns kills were claimed: A-10s vs helos. In another engagement, a helo was destroyed by a laser-guided bomb. In other words, "A2A" bombs killed nearly as many a/c as guns in the Gulf War. Iraq also lost 3 a/c to CFIT.

And yes, we make supremely better missiles today.

Early AAMs were more akin to guided cannon shells: narrow field of view, short range, and low maneuverability; often only chased a target in front of them (tail chase).

Modern AAMs (HOBS, LOAL) have comparatively stupendous ranges: a modern SRAAM (188 lb AIM-9X Sidewinder) has roughly the range of the original AIM-7 Sparrow (a much larger 500 lb MRAAM); and the new AIM-120D AMRAAM (335 lb MRAAM) has nearly the range of the legendary AIM-54 Phoenix (1000 lb LRAAM).

You will not easily outrun a Mach 3 missile pulling 50 g's with a 200° field of view. Why turn 720° when you can shoot almost directly behind you? (video of AIM-9X testing, 2000). (Realistically, some level of maneuverability is required for good shots, but far less than for a guns solution.) More videos, gifs, gfys, and MICA.

Reliability. In ODS: shot 28 AIM-7s at BVR, 22 hit the target or fireball; 10x more reliable than AIM-7s in Vietnam.

Essentially, missiles are now far better dogfighters than fighters.

But the best dogfighting weapon by far is neither gun nor missile: it's a wingman. Fighters don't fly alone. When you dogfight, A) you rapidly bleed speed and altitude, and B) your SA evaporates because you can't afford to focus on anything else except the guy you're turning with. You're effectively a sitting duck and blind, an easy target for anyone outside the fight.

Dogfighting is extremely dangerous. Two modern fighters are liable to both die in a dogfight, ie a kill/loss ratio of 1:1.

I know of no pilot who prefers dogfighting over taking BVR shots.

Dogfighting may not be dead. But it sure is on life support.

Resources

CSBA: Trends in Air-to-Air Combat: Implications for Future Air Superiority --- essential reading
The Radar Game --- Radar and stealth primer. Requisite reading.
RadarTutorial.eu --- radar tutorial. How radars work. Very useful explanations. Explains some of the limitations/necessities of targeting/guidance.
Gulf War Air Power Survey (GWAPS) --- how the Gulf War air campaign was fought (these are some of my notes; the entire report is ~3500 pg).
War with Iraq: Critical Lessons --- General Glosson's book on the war (he orchestrated and designed the campaign) and "explains the deeper strategy and thinking behind the air campaign"
A great selection of books on ODS.
Air Warfare in the Missile Age by Lon Nordeen. Covers every major conflict from 1965 to 2003.
Modern aerial warfare and doctrine.
RCS values on Global Security. Note that the F-35 values were estimates from early in the JSF program, before any production airframes were built. After the F-35 had been built, flown, and tested, officials from the test program (including a pilot) went on record saying the F-35 was actually stealthier than the F-22.
Resources I most frequently recommend

Glossary:

1

AAM - air to air missile
a/c - aircraft
Allied Force - NATO bombing of Yugoslavia, Kosovo War
HOBS - high off-boresight - describing very agile missiles with a wide field of view
LOAL - lock-on after launch
ODS - Operation Desert Storm, part of the Gulf War
RCS - radar cross section
RF - radio freq

2

EO - electro-optical ("telescope")
EOST - " "
IRST - IR search and track ("IR telescope")

3

SR - short range
MR - medium range
LR - long range
VLR - very long range

4

BVR - beyond visual range
WVR - within visual range

5

LO - low observable - ("stealth") a broader term, sometimes interchangeable with VLO
VLO - very low observable - ascribed to only "true" stealth platforms - eg, F-117, B-2, F-22, F-35

(30,000 character limit exceeded)

Placeholder: kinematics still matter

Placeholder: Alleged flaw: Dogfights are more common if US fought USSR instead of easy foes. Why would an adversary with better, longer-ranged sensors and weapons want to get closer where he is also more vulnerable? Related: Combat between peers results in dogfights. Most kills during the 80s resulted from the 8-year Iran-Iraq war between pretty evenly matched opponents. Missiles still dominated. Related: Comparison isn't fair; US had better tech. That's the point. Don't want to fight fair. If high-tech produces fantastic victories, then high-tech sounds like a good idea.


Are there any fly-by-wire airliners with negative or near-neutral pitch stability? Are any modern commercial airliners with fly-by-wire flight control systems designed with negative or near-neutral pitch stability so that they can take advantage of the capability of such systems to reduce trim drag and increase fuel efficiency?

If so, which aircraft are so designed?

And if not, why not?

In the images, the aircraft with positive static stability must produce sufficient wing Lift (the green arrow), not only to hold the aircraft up, but an additional amount to compensate for the lift from the tail surface, which is pulling the aircraft towards the dirt. The total aerodynamic force is the sum of the Wing Lift plus the tail plane lift, which must equal the weight of the aircraft plus twice the lift produced by the tail. THIS MEANS THAT IN AN AIRCRAFT WITH POSITIVE STATIC STABILITY, THERE IS SIGNIFICANTLY MORE TRIM DRAG AND THRUST REQUIRED.

In an aircraft designed with negative static stability, (bottom image) The wings, (Green arrow) plus the tail plane, (blue) both contribute to positive (upwards) lift, and so the total aerodynamic force is less, therefore the induced drag is less, and the thrust required (and fuel flow to generate that thrust) is reduced in comparison to an aircraft with positive static stability..
if you would like more details, review this video, from which I quote (at about the 1:00 minute mark), speaking about general aviation aircraft with positive static stability,  "... Something not very pretty about this situation, [positive static stability], is that we have this downwards acting lift force[ at the tail], which we call Trim Drag, which essentially, in a negative way, impacts our range and endurance, and which we'd like to avoid...", and then later, talking about the negatively stable F-16, at 1:50 minute mark, "In this situation we have, [at the tail], an upwards facing Lift force. This means ... we have, as it should be, all the lift facing UP. This means [my italics], we have an increase in our range and endurance performance.."

And, in addition, from this link, I quote "unstable designs get a slight reduction in drag and a slight increase in lift".  The rest of this article is also very informative.

To further illustrate the difference, below are two photos, of aircraft on final approach to land, where the flight path is stable and descending.
1. An F-4, with positive static stability, and 2. an F-16, which has negative static stability. Note the relative positions of the stabilators on the two aircraft, and especially, the relative angle of attack of the stabilators as compared with the AOA of the wings. In both of these pictures the aircraft is descending to land, so the relative wind is from the left, and below.

No.

Modern FBW airliners use less static stability than what the early jets were used to, but stability is still positive. The negative camber at the root airfoil of sweptback horizontal tails might indicate predominantly negative tail loads, but is also used to keep the isobars on the swept surface parallel. Also, the bent-up leading edge delays separation with full wing flaps when the tail has to produce lots of downforce:

A380 tail (picture source)

Boeing 787 tail (picture source)

At zero static stability the lengthwise position of the center of gravity coincides with the neutral point such that the lift per area on all horizontal surfaces is roughly the same (I neglect camber effects for the moment which are small in cruise configuration).

The horizontal tails even of the most recent designs still have negative camber and no twist which indicates that their design lift coefficient is around zero or even slightly negative. This has mostly to do with the tail loads in landing configuration but also shows that at transsonic speed they fly at a lower lift coefficient than the wing. Such an airfoil camber would make operation at transsonic speed and the lift coefficient of the wing rather inefficient.

A neutral stability design would make the FBW system even more flight critical than it is already and would make the "direct law" mode of the Airbus FBW system rather dangerous. Certification would be much harder - after all, FAR $25.173 still applies:

  (a) A pull must be required to obtain and maintain speeds below the specified trim speed, and a push must be required to obtain and maintain speeds above the specified trim speed.

The "maintain" part of this rule can best be achieved with positive static stability.

Also, reducing static stability beyond a point where stability is still slightly positive does not improve efficiency anymore. Note that the tail surface aspect ratio is smaller than that of the wing. If both surfaces would fly at the same lift coefficient, the induced drag from the tail would be relatively higher (in relation to lift) than that of the wing, even without downwash effects. This means that the lift at the tail comes at a higher price and it is more efficient to fly the wing at a higher lift coefficient than the tail.

EDIT:

Supersonic aircraft benefit from negative static stability because this will cause less trim drag in supersonic flight. No such advantage exists for airliners because they are not made for sustained supersonic operation.

Also, positive static stability is possible with lift on the tail. In that respect the question repeats an old meme. It is not the sign of the lift on the tail surface which determines the boundary between positive and negative stability, but the relative lift per area. It must be less on the tail than on the wing for stability. How else would a stable canard airplane be able to produce lift on its main wing?


Velocity of air flow around aerofoil To find the velocity of the air flow at each section of the aerofoil, am I right to say that the horizonatal velocity of the air flow is constant throughout the chord while the vertical component of the velocity varies along the chord depending on the angle of chord w.r.t. horizontal?

So velocity at first plane is $\frac{U}{cos\beta}$?

If that is the case, will shifting the air upwards, not push the wing down? Or am I right to say that as the airflow around the wings, there is no net upward motion of air, thus it does not push the wing downwards?

No, you can't say that the horizontal component of velocity is constant throughout the chord. There are few reasons why not:

1) From the formula you provided (which is correct if your assumption on velocity components is true for an aerofoil) we can see that as beta gets bigger the final velocity tends to infinity, which of course cannot happen.

2)The velocity change on aerofoil is dependant upon its pressure change, it reaches maximum at the point of maximum camber and not at the point of maximum thickness and I think that as per your theory it would than be reached at the point with maximum thickness.

3) Third and probably the most important thing is this: Lets imagine the flat plate aerofoil at some small angle of attack. The plate will produce lift, and the particles above an aerofoil will reach the trailing edge first. Since the airflow above aerofoil will be deflected by the same angle as below the aerofoil, by above stated theory, particles should reach the trailing edge at the same time because of a constant horizontal velocity. Which isn't true.

Second part of the question is correct, there is no net upward motion of air. In fact, there is a net downward motion of air behind an aerofoil called downwash. Basically how much the force wing exerts on air by deflecting the partincles down, by that amount of force the aircraft will be pushed up. Newton's third law.


How minimum runway length is calculated for PAC P-750 XSTOL? I'm not a pilot, but have interest in the question from a safety perspective, as a skydiver and drop zone operator.

I read the POH of PAC P-750 XSTOL, and tried reading a bit about the calculations, but could not make it out.

Given the parameters below, how is the minimum runway length is calculated for PAC P-750 XSTOL?

Parameters:

Pac 750 XSTOL
15 knots cross wind 90
0° flaps
6500 LBS TOW
Runway is 1500 feet above MSL
ISA +10°

You can't, at least not on the basis of the POH you linked. Taking off with 0° flaps for that aircraft is outside the POH limitations chapter.
2.20 Flap Limitations:

Approved flap ranges.
TAKEOFF FLAP: 20°
LANDING FLAP: 40°

4.27 Amplified Procedures - Normal Takeoff):

A wing flap setting of 20°  is recommended for all takeoffs. 20° flap
will provide the best takeoff performance. The Normal Takeoff
technique is to be used for Short Field operations and is the
technique used to derive the performance data in Section 5.


Why does GBAS broadcast Final Approach Segment data when SBAS does not? Ground Based Augmentation Systems broadcast message four, the Final Approach Segment, along with corrections for GNS signals in messages one and two. Since the FAS is essentially a semi-static approach plate, it seems like it could be distributed by subscription along with all the other info in a flight database instead of wasting VHF link bandwidth as it does. In fact, the Satellite Based Augmentation System uses the flight database subscription method.

For SBAS, the FAS data block is stored in the aircraft’s navigation database, while for GBAS the FAS data block is broadcast as a VHF data message.

What was the purpose for the GBAS design choice? It is impossible for the SBAS system to do this, but once the less constrained method was established, it seems like both systems should use it.

The reasons GBAS and SBAS are the way they are goes back to decisions made in the early 1990's when the concepts were first proposed. When the push started for satnav approaches it was obvious that augmentation was necessary to meet the accuracy and integrity needed for approach procedures. The FAA tasked RTCA to develop the standards and that was delegated to Special Committee 159 (SC-159).
SC-159 is a very large committee with representatives from government agencies, airlines, aircraft manufacturers, general aviation, avionics suppliers, and pretty much anyone with an interest in the system. Because of the huge amount of work and the differing systems the work was broken out to separate subcommittees. So while there were some people working on both subcommittees, the subcommittees each took there own path.
GBAS was being promoted by the FAA to be a functional replacement to ILS with support for CAT I and eventually CAT II/III operations. This needed support of the airlines who were only willing to go along if it didn't add significantly to their costs (preferably it would provide capability where ILS wasn't feasible and give them additionally capability at little to no cost.) So a fundamental goal of GLS was to be as operationally similar to ILS as it could get - minimal crew training, minimal aircraft system changes.
That last bit is key as the ILS is a DAL A system tied to the autoland system which is very expensive to certify. The avionics solution to this is the multi-mode receiver (MMR), ref: ARINC 755. The MMR allowed for retrofit as it occupied the same package as the legacy ILS receivers.
The MMR added a GPS sensor (which wasn't standard in the early 90's) and it allowed for integration with the ILS and its interfaces. The first MMRs were just and ILS and GPS sharing a box. But later versions added a precision approach navigator (PAN). The PAN could use the ILS output busses to provide the "ILS Look-Alike" output. But the GPS needs the augmentation data. This is broadcast from the GLS ground station on a VOR/ILS frequency. So the ILS receiver (a software defined radio) is repurposed in GLS mode to receive and decode the VHF data broadcast (VDB) from the ground station. It can then provide the augmentation data to the GPS and the FAS data to the PAN.
The reason for the FAS data being broadcast and not being in the nav database is that database is located in the FMS, not the MMR and the FMS is not a DAL A system. It also follows the concept that the ILS/GLS is a stand-alone unit that can support a precision approach even if other systems have failed.
Conversely, SBAS was pretty much ignored by the airlines (they only added WAAS GPS receivers when ADS-B drove the need.) SBAS was championed by the general aviation community that want RNAV approaches into airports that didn't have good approach options - no ILS, maybe a VOR or NDB approach. An RNAV approach was a big step up. Due to the large number of small airports that desired the capability, SBAS was more cost-effective than a GBAS approach. It was also cheaper for the user as it was contained within the GPS navigator/FMS. The limited bandwidth of SBAS forces the procedure data to be included in the nav database. But SBAS will likely never go beyond LPV capability which is acceptable to the GA community.
So the different needs of the GBAS and SBAS resulted in the different solutions.


How much fuel is burned to carry the trip fuel? For rockets, there is a rule of thumb that says for each kilo of fuel put into orbit, 7 kilos is needed to get it there.

For long and ultra-long flights, it feels intuitive that some very significant proportion of the fuel, perhaps the majority, is needed to carry the fuel needed to complete the flight. In other words, imagine that the fuel was weightless and 50,000 litres were needed. But since fuel is not weightless, the requirement is actually 100,000 litres.

Of course there are a lot of variables and it's fairly easy to calculate, but is there a rough and ready rule of thumb?

The 7:1 rocket figure is perhaps for the unrealized single-stage-to-orbit, getting a payload to low Earth orbit (LEO) is closer to 9:1, and going to the moon and back is 23:1 (Saturn V).
If a soda can's content is the fuel, then the rocket stages that are jettisoned have better fuel to empty mass ratio compared to that soda can, so staging is not the main reason why the figures are higher than the 7:1.

This is important because if a 5-hour flight is getting to LEO, then an ultra-long-haul 16-hour flight is the equivalent of going to the moon and back.

This already tells us there is no general rule of thumb for flight planning (or space flight). But, there is a common figure that is used when highlighting the benefits of carrying the right amount of fuel.
0. A common figure: 15%.
According to Simon Weselby, a Fuel and Emissions Performance Manager at Airbus, that figure is 15%. So to carry 1,000 kg of fuel, an extra 150 kg will be burned.
According to the famous lift-to-drag ratio graph, carrying fuel in cruise is not a big deal as the induced drag decreases with speed. The challenge is getting a heavy plane off the ground and getting it up to speed.*
If the fuel fraction mid-flight for a long-haul jet is 20%. Then that means the thrust required to carry 20% of the weight is 10% of the thrust (if the induced drag equals the form drag at the minimum drag point).
* That's why above a certain range, it becomes more economical to make stops. This takes into account the fuel alone. Not taking into account the passenger convenience, aircraft cycles, the maintenance cost of the extra takeoff thrust, etc.
That relationship is demonstrated by the graph below.
(Wikipedia) Takeoff, climb, step-climbs, etc., are accounted for, i.e., those are the averages for complete flights, not just cruise.
I've used the same 777-200 data that was used in making that graph to come up with different ways to look at your question, which can be answered in more than one way (the previous 15% figure is the easy answer).
1. If the fuel was weightless problem first.
I've used the most economical range (average fuel flow) as a baseline. And from there found out how much fuel is wasted to carry the extra fuel for the extra range.
NM      kg

2800       0    0%
3200     230    1%
3600     420    1%
4000     750    2%
4400    1130    2%
4800    1760    4%
5200    2350    4%
5600    3180    6%
6000    4060    7%
6400    4990    8%
6800    6080    9%
7200    7260   10%
7600    8590   11%
8000    9970   12%

Going from 2800 NM to 8000 NM, 9970 kg are wasted carrying the heavier fuel, or 12% of the total fuel load.
The fuel fractions for 2800 NM and 8000 NM are 18% and 40%. The aforementioned 15% figure for the A330 at 2500 NM matches that of a 777-200 at 2400 NM.
2. Problem two: carrying more fuel for the same trip distance.
This is equivalent to payload. What it does is increase the landing weight (LW). A quick and dirty way to check how much extra will be burned carrying more fuel that will not be used is to use the same fuel fraction for that distance.
This is what the Airbus presentation says, which I've been able to verify in a spreadsheet for 5 different weights 22.7 tonnes apart. (And also for the 737 for good measure.)
(Own work) Click to view full table.
For example, if our baseline flight needs 15% fuel fraction, it will still be 15% of the new higher weight (landing weight + trip fuel). In other words, if the LW goes up, the trip fuel goes up.
For the 777-200, landing weights of 136,100 and 226,800 kg need 25,400 and 37,800 kg of fuel for a 2400 NM trip. Or 15.7% and 14.3% fuel fractions.
An 8000 NM trip needs a fuel fraction of 40.3% for the lowest landing weight I calculated, and 38.8% for the heaviest.
So the quick and dirty rule of thumb is to maintain the fuel fraction for the same trip distance.
3. Percent of Landing Weight (LW) per hour.
A different way to look at it: I've constructed the graph below for the 777-200. As you can see, it matches the trend of the Wikipedia one.
(Own work)
So for a 6-hour flight, it will be 6 times 3.6, or 21.6% of the LW in fuel.
While a 0.5% is negligible for a 737 and maybe even for a 777 on short routes, it is not when it is multiplied by long flight durations.
Below is yet another way to look at the data, the average fuel flow per engine in kg per hour for the different trips.
NM      FF/eng (kg/hr)

 800    2510
1200    2460
1600    2440
2000    2450
2400    2450
2800    2450
3200    2470
3600    2480
4000    2490
4400    2510
4800    2540
5200    2560
5600    2580
6000    2610
6400    2640
6800    2660
7200    2690
7600    2720
8000    2750


Differenciate- the motion of "Nose-up trim" and "Nose-down trim" I wanted to understand a part in ‘Take Off” where the study starts to explain “… the airspeed for best rate of Climb.”
I am a little confused about the (how to) of pushing the wheel forward to relieve forward pressure
 (nose down trim) -or- Rotate the trim-wheel back towards you to relieve back pressure (nose up trim).
 Is the motion in opposite of when pushed down, nose up trim and vice versa to that motion?

Hope I am explaining it articulately and its comprehensible.

There are two pitch inputs* in the cockpit: the yoke and the trim wheel. The effects add up - you can achieve the same pitch up moment by the yoke only, the trim wheel only, or a combination of the two. The pitch up or pitch down motion of the airplane is always the sum of the two.

*That is not a very correct statement, but for now let's put things that way for easier understanding.

The difference between the yoke and the trim wheel is that once you let go of the yoke, it returns to neutral. However the trim wheel stays where it is.

So let's say you want 2 units of "pitch up force" (and let's ignore what the actual unit in physics is, it is just a number) in a certain flying situation. You pull on the yoke until you reach the desired pitch. Great. However if you let go of the yoke, you will loose that pitch up force and the aircraft will start to pitch down. That is not what we want - we want the airplane to hold this pitch attitude, stable, for the next 10 minutes. If we move the trim wheel from the neutral position to 0.5 units up, the desired amount of pulling on the yoke is reduced - we still need to pull back on the yoke, but not as much - we only need 1.5 units of pitch up on the yoke because the other 0.5 units is provided by the trim wheel. This is what "relieve back pressure" is referring to. If you move the trim wheel to 2 units up, you can now completely let go of the yoke, and the aircraft is stable.

  Is the motion in opposite of when pushed down, nose up trim and vice
  versa to that motion?

I think you might be confusing the pitch input with the movement of the trim tab on the elevator, assuming that your textbook mentions it. On most general aircrafts, a trim tab is used for pitch trim control. A trim tab is essentially "an elevator of the elevator". The elevator needs to move up for the airplane to pitch up. But the trim tab needs to move down for the airplane to pitch up.

Do not confuse how the trim is achieved aerodynamically, with what you input in the cockpit. The trim tab is just one of many ways to control pitch trim. Airliners, for example, do not have a trim tab. However, the principal of operating the trim wheel is the same. It is just a large aircraft uses a different method to hold a stable pitch attitude.


What are possible explanations for fuel being expelled in this video? In another question, I asked about whether or not a fuel spill would be reportable or not. The answer was "no", because the aircraft was not in flight.

What are the possible causes of the spill demonstrated by this video?

I can think of 4 possible causes, 3 of which can probably be discounted.

Tank venting. The fuel system is designed to deliberately "leak" if
the tanks are overfilled or, the fuel expands due to temperature
changes. Whilst I haven't seen this happen on a B767, I have seen it
on numerous other types and when it happens, it does not gush out
like it does in this video.  It's more of a seep of fuel which drips
off the underside.  Whilst it can be a lot of fuel, this video does
not fit a venting scenario.  Additionally, the flight crew would be
very familiar with venting which would be a normal event and would
not have abandoned the flight.
A fuel leak such as a ruptured pipe, a failed seal and so on.  I
would expect to see fuel ejected like this but only from a
pressurised part of the system, downstream of the fuel pumps.  The
location of this leak is not from a pressurised part of the fuel
system and in my opinion, there is simply too much fuel for it to be
a result of gravity.  It also appears to be coming from a nozzle
rather than seepage
As can be seen in this video, the source of the fuel is
coincident with the location of the fuel dump nozzle.  It is
possible that the crew accidentally activated the fuel dump but
unlikely (inconceivable?).  The switches are very clearly surrounded
with "don't touch this" markings and require two separate switches
to be activated.  Additionally, the jettison valve switches are
"guarded" such that you have to lift a spring loaded flap up in
order to be able to press the button.
The APU draws it's fuel from the left main tank. This flight was
close to the  maximum range of a 767 so  would have been at or close
to maximum fuel load. If the APU had been running for a long time,
longer than expected, it's possible that the crew started a fuel
transfer to balance the tanks by pumping fuel from the right tank to
the left tank and forgot to switch the transfer off.  This could
have pressurised the left tank causing fuel to overflow into the
surge tank and vent out (the surge tank vent is also very close
to the jettison nozzle).  I believe that this is the most likely scenario.

This is the only authoritative source I could find showing the fuel jettison switches.

All supposition of course but a strange incident.  I'm sure there may be other possible causes and I'm sure that comments and other answers might expand on this.


Can radar detect a small flying device with MEMS microengines? I have seen some MEMS micro engines and some micro turbines and I would guess they can be attached to some payload to fly. Is it possible for commercial/military radars to detect those micro flying devices?

Obviously the MEMS engine itself is not going to be detected: they're only a few millimetres across. The question entirely depends on what you attach it to.
Conventional radars have trouble detecting UAVs less than a couple of metres long, and replacing their power plants with micro turbines won't change that.

My neighbours at Aveillant already have a holographic radar system that can detect smaller targets such as UAVs more accurately. Again, changing the power plant technology won't change that.

Micro-turbines are not intended to replace propulsion systems, but to replace batteries, allowing them to use denser hydrogen, methane, or methanol fuel. As far as I've been able to find, they don't produce break-even power yet, but it's envisioned that they will become commercially relevant once they can produce more than 10 W (about .01 hp), in a few years' time. For comparison, a current, small, military UAV might generate tens of horsepower, and some experimental super-lightweight UAVs need as little as 5 hp, but with no payload or cargo.

TL;DR: (a) MEMS turbines aren't going to be relevant for UAVs for some years, and they'll have to be much bigger than they are now; (b) replacing the power plant won't make much difference to the radar signature.


Why are the engines not tucked underneath the wings of airliners? If you look at the engines of an A350 and other similar aircraft, you will see that their engines stick out ahead of the wing. Why? Why aren't they tucked under the wing?

(Source: Airbus)

To bring the Center of Mass forward, and to be able to raise the jet engines, which then permits shorter and lighter landing gears.

This is what the 737 did when it moved to the bigger CFM56 engines:

Old vs new:

(Top, bottom)

Related: Why do we use pylons to mount the engines on jetliners?


What does pre/post modification mean in Airbus MPD? What is the difference between POST MOD (with partial mod i.e SXXXX) and PRE MOD (with partial mod) in the applicability column of an Airbus MPD (Maintenance Planning Document)?

It means that operator have to check what status of the particular MOD have the subject A/C, pre or post. Therefore it affects operators MP.


Are there any aircraft where minimum-V1 is limited by Vmcg? V1, unlike all the other Vspeeds, is not rigidly determined by the laws of physics, the aircraft’s specific abilities, and the conditions of the particular takeoff being attempted,1 but is, rather, chosen by the pilots from a range of possible V1s.

The lower limit of this range is generally set by the speed past which the takeoff can safely be continued while maintaining adequate obstacle clearance, even in the event of an engine failure (henceforth known as the first-safe-go speed).
The upper limit of this range is set by the speed past which the aircraft can no longer be guaranteed to stop on the runway in the event of a maximum-effort no-reverse-thrust rejected takeoff (henceforth known as the last-safe-RTO speed).

However, if an aircraft is sufficiently light and has sufficiently-powerful engines (especially if said engines are mounted far from the aircraft’s centerline), one could potentially conceive of a situation where the lower limit of the V1 envelope is not, in fact, determined by the first-safe-go speed, but, rather, by...

...the speed below which the aircraft has insufficient rudder authority to maintain directional control at takeoff thrust in the event of an asymmetric engine failure (known as the minimum controllable speed - ground, or Vmcg).

Such a light, sporty aircraft could easily have a theoretical first-safe-go speed that is lower than Vmcg, as low total weight and high thrust-per-engine both decrease the first-safe-go speed,2 and, simultaneously, increase Vmcg.3  This would force the lower limit of the possible-V1s range to be set, not at the theoretical first-safe-go speed, but, rather, some distance above that, at Vmcg (as an asymmetric engine failure at or above the theoretical first-safe-go speed, but below Vmcg, would result in an immediate loss of directional control, necessitating a rejected takeoff).  For added complexity, some aircraft have engines at varying distances from the aircraft’s centerline (for instance, a trijet with one engine slung under each wing and one mounted in the tailcone, or a quadjet with one outboard and one inboard engine slung under each wing), resulting in different Vmcgs for different engine-out scenarios, such that, at a given speed, an aircraft might be able to safely continue a takeoff if a centerline or close-to-centerline engine fails, but would suffer a loss of directional control, and have to reject, should a far-from-centerline engine fail.

Are there actually any aircraft for which the minimum-allowable-V1 is limited by Vmcg, rather than the first-safe-go speed?

1: ...except in the special case of the aircraft being at exactly its maximum allowable weight for the takeoff being attempted, in which case there is only one possible value of V1.

2: ...as a lighter aircraft needs less speed (and, thus, less thrust) to become airborne, and an aircraft with powerful engines has more thrust to work with in the event of an engine failure.

3: ...as an aircraft with powerful engines needs more rudder authority (and, thus, more speed) to maintain directional control with an asymmetric engine failed and the other(s) at takeoff thrust (a problem which grows steadily worse the further the asymmetric engine(s) get from the aircraft’s centerline, due to the larger and larger yawing moment arm generated as they move away from the centerline), and a lighter aircraft has less weight on its landing gear (and, thus, less traction force acting to resist the yawing moment from an asymmetric engine failure).

Yes

Almost any transport category jet will reach its Vmcg V1 limit in favorable conditions.

The rationale is quite easy: When fully loaded with heavy fuel load (ie. at maximum takeoff weight) some 20% of weight is payload and about 20% is fuel. When the same jet is taking off with light passenger load for a short hop with low fuel load, there is massive surplus of thrust available so there is some acceleration available in case of engine failure on ground. This is especially true for twins.


Why would a pilot request an unusual approach/runway to ATC? In another SE Aviation question about the preferred approach for commercial aviation (Visual vs ILS) there's the following useful explanation:

  In most ATC facilities, the Tower decides what runway to use, and the
  approach control calls the type of approach generally on offer(this
  can vary depending on facilities and how they agree to run things). A
  pilot can always request a different approach... they might be
  delayed, sometimes significantly if they insist on something way out
  of the loop

I'm curious what would be examples of a pilot insisting on "something way out
of the loop"?

What's the preferred approach for a passenger jet?

For currency, airline pilots have to do various approaches every so often to remain current or for the plane to be current (RNAV/ILS Cat II/III approaches). So, every now and then when coming to another airport they could request to shoot that approach instead of the one being used. Sometimes it's a non event (no traffic, or the few other aircraft either fit well before or behind them); other times, it could hinder the flow of operations if they're allowed to do full or certain procedures (various circling to land procedures).

Another very common request that falls in this category is to land or depart in the opposite direction of what's being advertised. This in recent years has become more cumbersome for controllers (due to more and new rules implemented), so it's being used less often.

Sometimes when there's little traffic it's fairly easy to accomplish this kind of arrival or departure. Other times, it becomes a nightmare, and unless it's operationally mandated the pilot will be told, unable opposite direction, due to traffic. When it's operationally needed, then it will be told to hold somewhere to wait until there's space to get them out for departure; or vectored around or put in holding if needing to land opposite direction, and they can be accommodated.


How do airlines provide crews for the return leg of a long-haul flight? In a video, a Swiss International Air Lines crew flies an Airbus A340-313 (flight LX38) from Zurich to San Francisco. Then, they can be seen (I am not sure if this is on the very same day) visiting downtown and the Golden Gate prior to getting back to the airport for the return flight (LX39), which is scheduled for departure around three hours later.

The question here is:

How do airlines handle crew turnovers in long-haul flights?

Is it the same crew who is demanded to command the return flight? Or is there, oddly enough, a replacement crew in each destination airport? Or do they carry the crew for flight LX39 onboard flight LX38?

You presume that they flew back the very same day... but that is an incorrect presumption.

For long flights over about 8 hours, strict rest limits apply so they cannot fly again for 8-10 hours at a bare minimum. Typically, a crew from a long-haul flight will stay in a hotel in the destination city for anywhere from 12 to 48 hours, depending on the flight length, timezone changes, airline schedules, union contracts, and so on. Yes the hotels and travel bonuses costs the airline a pretty penny but that's the cost of doing business.

So at this very moment there will be 1 or maybe 2 LX crews, resting (or touristing...) in San Francisco, waiting to fly a return service.

For more information you can google or ask a new question on Fatigue Risk Management Systems.


What altitude should you cross DBIGE at on the PALLEY FIVE Departure (SID)? While at Henderson Executive airport you receive an IFR clearance containing the phraseology "Climb Via the PALLEY FIVE Departure, Coaldale Transition" and you receive no additional altitude assignments from ATC at what altitude should you cross DBIGE at?

As it reads:

....on assigned transition, maintain FL190, expect filed altitude 10 minutes after departure.

If no instructions are received after 10 minutes, remind the ATC. From the FAA FAQ:

Q. I am cleared to "Climb Via SID". What if there is a published altitude restriction at a fix that is higher than the charted "Top Altitude"?
A. You are only cleared to the charted "Top Altitude" contained in the narrative of the procedure, unless ATC assigns a different altitude.

From the AIM:

SIDs will have a "top altitude;" the "top altitude" is the charted "maintain" altitude contained in the procedure description or assigned by ATC.

Consider a charted top altitude as the equivalent to a verbal "except maintain." As "except maintain" also does not cancel the restrictions below it. I believe this makes it easier to remember.


Does the extension of trailing edge flaps increase or decrease the critical angle of attack? Which graph is the correct representation of the trailing edge flaps' effect on the critical angle of attack? Does their extension increase (as depicted on the first graph) or decrease (as depicted on the second graph) the critical AoA?

Both right and both wrong, both over simplifications based on unknown airfoils, and so on. Real aerodynamics is complicated and 3 dimensional.

Flaps usually increase the critical angle of attack a few degrees, but they also increase the effective angle of attack for a given pitch. So the net result is that the pitch of the aircraft will be similar at stall with or without trailing edge flaps, but the true AoA will increase.


Departure and arrival fix loading via FAA website About 8 years ago I was involved in a project that would hit an FAA website for fix loading. It was departure and arrival fixes and their associated data. The URL included a command line where you could request an airport, date, time, and increment. Does anyone know what happned to that site or if there is a replacement? The data looked something like this:

The FAA has a graphical display of forecast arrivals by arrival fix for airports in the Airport Arrival Demand Chart. Choose a time interval, airport, and select "arrival fix." If you look at what it's doing through a network inspector, you'll see it's fetching JSON data, if you're looking for programmatic access.

That page only shows arrivals, not departures though.


Why disable stall warning based only on low airspeed, rather than multiple criteria? One of the factors that potentially contributed to the Air France 447 crash is that the stall warning was disabled when the airspeed fell below 60 knots.

I understand why this is -- you don't want to have the stall warning go off while the plane is parked at the gate or slowly taxiing.

However, this seems like clearly bad design for two reasons (that should have been obvious to the designers):

This introduces an extra point of failure. If the pitot-static system fails, then the stall warning may be disabled due to erroneously low reported airspeed.
As demonstrated by AF447, a stalled plane may have very low forward airspeed in an extreme stall.

Moreover, it seems like the solution is easy: Only disable the stall warning if a number of criteria are met. For example, the following logic could be used.

  The the stall warning (based on AoA vanes) is disabled if and only if (i) the forward airspeed is below 60 knots AND (ii) the landing gear is down/on the ground AND (iii) the radar altimeter reports a height of 0.

This logic would still prevent erroneous stall warnings on the ground, but it is more unlikely to suppress "real" stall warnings, as it would require multiple systems to fail.

Alternatively, if you are worried about one broken sensor resulting in erroneous stall warnings, you could require only two of the three conditions to hold for the stall warning to be disabled. That's still better than only one condition.

My question: Why do aircraft not use multiple criteria, such as suggested above, for disabling the stall warning?

The point of my question is that you want the stall warning disabled when the plane is on the ground. Whether or not the plane is on the ground should be rather obvious and you should not need to try guessing whether the plane is on the ground based on airspeed alone. There are plenty of other sources of information that can indicate whether the plane is on the ground.

A review of the stall warning system was recommended in the final report:

EASA require a review of the conditions for the functioning of the stall warning in flight when speed measurements are very low.

Here is the outcome of reviewing the "conditions" (plural):

EASA has reviewed the conditions for the functioning of the stall warning in flight when speed measurements are very low. The stall warning is designed to be efficient in a realistic and recoverable flight domain. It is also designed to avoid spurious triggering, hence the 60 knots stall warning inhibition threshold implemented on a large number of large aeroplanes. At very low speed (below 60 kts), corresponding to exceptionally high angle of attack, the aircraft flight characteristics are unknown. Flying below 60 knots is out of the flight envelope. Certification requirements are not established to ensure safe flight outside the aeroplane flight envelope.
Status: Closed — Category: Disagreement

While yes there are multiple factors in any one accident, the stall warning design was not one of the listed contributing causes. The biggest factor is that the plane was stalled by the crew. Tragic as it is.
Adding criteria to a system adds more points of failure to that system. As an example, if one RA (radio altimeter) is inoperative, the crew will have an erroneous stall warning on ground that they can't silence. The solution will be to pull a circuit breaker, but this might lead to a flight conducted with no stall warning.


What is the procedure following a near miss? This is a follow-up to this question - in particular, to this video posted in MichaelK's answer.

What would be the correct procedure for the pilot to follow in this situation?  (That is, after a near miss).  Should they report the incident to ATC immediately, even though the incident is over?  If there are differences in the procedure depending on jurisdiction, what would it be in the USA and the UK?

The categorization of nearly missing another plane is different between the UK and US. See: What is the relationship between the terms "airprox" and "near mid-air collision"?

UK

As for the procedure, for the UK (where it's called an AIRPROX) it should be reported over the radio if the controller's workload permits, else later in writing after landing.

  An AIRPROX Report should be made by any pilot flying in the United Kingdom Flight Information Region, the Upper Flight Information Region or Shanwick Oceanic Area when in his opinion, the distance between aircraft as well as their relative positions and speed have been such that the safety of the aircraft involved was or may have been compromised.

So if it is in the pilot's opinion that an AIRPROX took place, it should be reported. The message needs to start with, "AIRPROX report." Following the report it will be confirmed in writing within 7 days.

The contents of the message the pilot should transmit are:

  Aircraft Callsign
  SSR Code
  Position of AIRPROX Aircraft heading
  Flight level, altitude or height
  Altimeter setting
  Aircraft attitude (level/climbing/descending/turning) Weather conditions
  Date and time (UTC) of the AIRPROX Description of other aircraft
  First sighting distance and details of flight paths of reporting and
  reported aircraft.

Source: CAP 413

USA

Similar reporting is explained for the US in the FAA AIM 7−6−3 Near Midair Collision Reporting. They can also be reported after the fact in writing.

The reported items are similar to the ones above, extra items include but not limited to:

  Degree of evasive action taken, if any (from both aircraft, if possible).
  Injuries, if any.


Where can I find current downloadable tower, ground and approach frequencies for USA airports? I have searched the FAA site and cannot find a spreadsheet with current freqs for airports, only incomplete lists.  Online flight planning tools must get query-able current freqs on a monthly basis, but I sure couldn't find them.

I'm looking for what Airnav, the Chart Supp US, AOPA flight planner all provide if you search on a specific airport, but in a format I can query from a personal spreadsheet.

I have found something that will work. It is not pretty and I swear I can still smell the punch cards that produced the text files, but here it is:

https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/NASR_Subscription

It is free, it appears to be updated by the FAA, (I verified it has the current frequency for my local VOR that I know changed 2 months ago) and it is searchable.

Download the current zip file, use the .txt data layout files to determine where in the fixed length record of whatever file your desired data resides in is located.  I did a quick import into Excel and am able to strip the information that I need out based on position in the field.

Not the pretty spreadsheet I was hoping for, but ...

Thanks for the suggestions, everyone. If anyone knows any standard software for the NASR subscription (or what the !@*# NASR stands for), I'd be interested.


What is the difference between stopbars and Intermediate Holding Position Lights? I know that stop bars continuously light red and stand at before taxi route joint, holding points, or at the runway entrance, but what about the Intermediate Holding Position Lights? How can we differentiate between the  stop bar and Intermediate Holding Position Lights with regard to function and location or color? I added pictures below; I am sure of the stop bar, but am I correct about the Intermediate Holding Position Lights? Btw; there is a definition for Intermediate Holding Position Lights: A set of three amber lights or full red stop bar are provided at intermediate taxiway holding positions.

Intermediate position holding lights may be used at larger airports as an additional means of controlling traffic while moving on taxiways to give way for other surface traffic an a taxiway intersection.  Stop bars are used to provide additional identification of the boundaries of runway safety areas and ILS critical areas to prevent runway incursions.


What are these parts on STOL/bush planes? I've seen these (note the parts pointed to by the red arrows in the image) on the landing gear struts of Super Cubs and plenty of other STOL bush planes with large tundra tires. It looks like maybe just an aerodynamic fairing on the gas tube/strut of the landing gear but I'm wondering why on every example I've seen of this, the aerodynamic shapes are angled differently (one is more "up" than the other). What is this if I'm wrong about what it is and most of all why are they always angled differently? Is this to try and help with adverse yaw or something?

You can also see them in this video here (note that they, too, like all I've seen, are angled differently): FlightChops Super Cub

Those are not specifically STOL hardware, they are bungee covers that happen to have an airfoil shape.

Aircraft like the one in your picture use bungees (also called "shock cords") to absorb the force of landing: As weight is transferred to the gear the bungees are stretched. The installed bungees look like this:

The bungees are literally just "aviation-grade" bungee cords, and would be quickly deteriorated by weather if left exposed, so they are usually covered. The most basic covering is a leather or plastic boot:

The boots are not much more aerodynamic than the exposed bungees however, so some aircraft (including many with STOL kits) have a cover with an aerodynamically favorable shape to reduce the drag caused by the bungee bulge. That style of cover is what's shown in your picture.
Here's a closer look:


Can lift be equated to how much air is moved? The explanation for lift that I find easiest to visualize is that air is deflected downward by the wing. This downward action causes an equal and opposite reaction of an upward force against the plane, as in accordance with Newton's third law.

As you can see from the image below the red lines both end lower than they started.

Air at sea level weighs 1.293 kg per cubic meter. The acceleration due to gravity is 9.8m/s².

That comes up to 9.8N of force being needed to keep a 1kg aircraft in the sky. With perfect efficiency this equals 9.8 watts.

If trying to hover VTOL aircraft, can you multiply how much air a propeller can move, by how fast it moves it to predict lift force? Since force is mass x acceleration?

Or do fluid dynamics work differently as the air exiting the propeller will spread out instead of all going straight down? If that is the case can using a duct with a properly fitted bell nozzle solve this problem? Or am I thinking into realms that I shouldn't be?

First off, your calculation for 9.8 W does not seem to be based on any actual physics. Check the units! I can't tell if you did $P=F\cdot m$ or $P=\frac{F}{m}$, but the result is either the nonsensical quantity of joule-kilogram per meter, or acceleration respectively.

A correct calculation based on keeping something aloft by propelling air downwards would be as follows. To keep something aloft, you need to expel mass downwards at a certain speed. The force to keep the object aloft is $$F=m_{object}g$$ The force generated by downwards momentum transfer is $$F=\dot{m}v$$ with $\dot{m}$ indicating mass flow (kilogram per second) of the air (not the mass of the object). The energy flow (power) required to  impart this momentum on the airflow is $$ P=\frac{1}{2}\dot{m}v^2$$ Here we can draw an important conclusion. The power requirement is arbitrarily small, by increasing the mass flow and decreasing the downwards velocity. Immediately, you can see why helicopters have big rotors and airplane wings are so large: they want to affect as much air mass as possible for increased efficiency. Even flying faster increases lift efficiency (reduced induced drag) by affecting more air per unit of time. Of course, at some point other sources of drag will dominate.

The above calculations assume that force is purely generated by creating a downwards mass flow. This is not exact reality. For example, put your aircraft on the ground, and it does not sink through it even though no mass flow is created. When flying close to the ground, some of the airflow downwards creates a pressure due to hitting the ground below, which helps you keep aloft as well (this is called the ground effect). Other than that, viscosity plays a small role by generating a force opposite the downwards air movement (although viscosity is required for lift generation with an airfoil). However, to answer the main question: equating lift by how much air is moved is a very good approximation.

Let's finally address your idea of using a Bell nozzle. This is a nozzle that is used on supersonic propellants (the 'throat' of the nozzle marks the transition from subsonic to supersonic), and is used to increase the speed as much as possible. This is very inefficient in terms of energy, but since rockets need to carry all the propellant mass (whereas an airplane gets 'free' mass flow by travelling through air), and need extra propellant to carry that propellant up, speed wins instead of mass, and rocket engines are optimised for nozzle velocity.


Safest deck on multi deck airplanes It is a well known statistic that rear seats has higher survivability rates than front seats due to generally lower impact forces.

Double decks airplanes are not so common so statistics would probably be unreliable, especially since Boeing's only have a forward double deck.

Has any survivability study been made on that kind of aircraft, that include upper vs lower deck ?

I'm mostly interested in the a380 but other design are welcome as well.

Very difficult to say as we don't have enough real-world examples.

Vertical impact forces would be lower on the upper deck as the lower deck acts something like a crumple zone and absorbs some of the acceleration.
That said, an evacuation from the upper deck can result in more injuries due to the longer, steeper, slide that's needed.


Why is the Piper PA-23 considered a bush-plane, while the Beech 95 Travel Air is not? The Beech 95 Travel Air was developed as a direct competitor with the Piper PA-23. The Piper is considered a reasonably ok bush plane, yet the Beech 95 is not commonly seen as a bush plane (I don't think I've ever seen a Beech 95 on floats).

What difference makes that the one is suitable as a bush plane, while the other is not?

Beech 95 Travel Air

Piper PA-23

Without getting into the details of the two, there are going to be 3 factors:

Landing Gear suitable for rough fields.
Decent size cargo loading doors and cabin with cargo provisions.
Power to weight ratio suitable for short rough fields.

Neither of those airplanes are really purpose-built for bush operations, but to the extent they have those characteristics they could be said to be more or less suitable.

When the US Army was looking at the DeHavilland Canada Beaver, which WAS specifically designed for bush operations, being designed in response to an operator survey, there was a hue and cry from the US aviation lobby, prompting the Army to have a fly-off with the Beaver vs a motley assortment of "utility" aircraft put forward in haste by various manufacturers (including the Travel Air IIRC, and the Cessna 195).  The Beaver won without much difficulty, and the US Army went on to take nearly 2/3rds of Beaver production.


What causes pressure disturbances ahead of the wing? Can someone post a link to a video that shows an example of this either in a wind tunnel or using some other examples?

  When an aircraft is flying below the speed of sound, the pressure disturbances will be moving faster than the airplane (think ripples on a pond again), and those disturbances that travel ahead of the aircraft influence or “warn” the approaching airflow. This “pressure warning” can be observed in a smoke wind tunnel as it causes the upwash well ahead of the wing.

Quoted from Flight Theory and Aerodynamics

An approaching body needs to push air out of the way. Directly ahead of it, it will compress the air such that the local pressure increase will push the air out of the way. When the body is a lift-producing wing, the lower pressure on the upper side will suck the air towards it. So what can be observed are two effects:

Air gets compressed ahead of any body approaching at subsonic speed, the more the faster the body moves, and
When lift is created, this pattern will be distorted such that the flow will turn in the direction of the lift-producing suction.

The propagation speed of small pressure changes can be observed with your ears. Sound is just that: Small fluctuations in pressure. An approaching wing is just like an approaching siren, only that the siren emits an oscillating pressure variation and the wing an aperiodic one.

For the video my recommendation is

Note how the flow lines diverge ahead of the airfoil: This is where the flow is slowed down. At higher angles of attack you will also see how the flow lines bend up ahead of the approaching airfoil.


How to interpret the electrical information on a G1000 T206H? I have a T206H and The POH says:

  Current indication (AMPS) for both the main and standby batteries is
  provided at the bottom of the EIS bar (along the left margin of the
  MFD or PFD), labeled M BATT S. Main battery current is numerically
  displayed below the M. Main battery current greater than -1.5 amps is
  shown in white. Standby battery current is displayed numerically below
  the S. A positive current value (shown in white) indicates that the
  battery is charging. A negative current value (shown in amber)
  indicates that the battery is discharging. In the event the alternator
  is not functioning or the electrical load exceeds the output of the
  alternator, the main battery ammeter indicates the main battery
  discharge rate.

The part that confuses me is the one that says:

  Main battery current greater than -1.5 amps is shown in white.

Does that means that when the number is negative but greater than -1.5 it is OK, because it is in white?

And after 40 minutes of flight in normal daytime operations I have a -1.0 in the M BATT amps but the M BUS volts remain 28.3. What does this mean?

You've actually answered your own question back there:

  A negative current value (shown in amber) indicates that the battery is discharging. In the event the alternator is not functioning or the electrical load exceeds the output of the alternator, the main battery ammeter indicates the main battery discharge rate

The 28.3 Volts reading is the electric energy charge supplied by the aircraft alternator (60-Amp alternator is standard and a 95-amp one is optional) through the main bus, whereas the M amp reading is what's happening to the main battery. In the situation you've described, you've got so many electrically-powered systems running, that the alternator, though operating normally, is unable to supply them all, so additional power is drawn from the battery.

The 206 PIM states that the Main battery Ammeter is color-coded white for values greater than -1.5 Amps, meaning that Cessna is not concerned with battery drains of 1.5 Amps or less (i.e. readings between -1.5 and 0). If the discharge rate is greater than 1.5 Amps (reading lower than -1.5), then the reading will be color-coded yellow. See below for an example of this.


Can private pilots run other non-passenger flight businesses? As I understand it, private pilots can not take paying passengers.
(Friends on a flight can give the pilot strictly only the friend's share of fuel etc. costs.)
But in fact can private pilots

do aerial photography/videography and charge for it?
do reconnaissance/similar and charge for it?
deliver packages, or indeed cargo?
drop skydivers for pay
pull up gliders for pay

What's the deal on that?

According to the current FAA stance on the issue, none of it is allowed except glider towing.
The latest interpretation from the FAA that I'm aware of is the 2010 Perry interpretation, however, there was a conflicting letter (Del Rossi) from 1987 that said the opposite from the White interpretation.  The FAA further clarified the discrepancy between these two letters in 2010 with the Perry interpretation. (Note: this link contains both of those interpretations from 1987 and 2010 together.)
The FAA acknowledged the discrepancy in 2010 and determined that the older letter took precedence because it was issued by the national office, but the White interpretation was issued by a regional office, although on a later date.
For aerial photography and survey, if it is in furtherance of their own business and is simply incidental to that business, yes, they may perform the work as a private pilot according to the White interpretation.  The other interpretations, which take precedence say this is wrong.
If someone else hires them to fly so the passenger may do those things, it's definitely not allowed nor has it ever been mistakenly indicated as allowed by the FAA for private pilots in past interpretations.
There is the White interpretation from 1995 that incorrectly states:

To the extent that your operation would be in furtherance of your own
business of aerial photography or survey, and you are not carrying
persons or property for compensation or hire, then you may do so
holding a private pilot certificate. However, to the extent that your
operation would involve operating your aircraft as an aerial platform
for other photographers, etc., for compensation or hire, you would
need to be the holder of at least a commercial pilot certificate in
order to act as the pilot.

So, in short:

Do aerial photography/videography and charge for it? - No, but it was mistakenly allowed according to the White interpretation in 1995.

Do reconnaissance/similar and charge for it (aerial survey)? - No, but it was mistakenly allowed according to the White interpretation in 1995.

Deliver packages, or indeed cargo? - No, this would be carrying property for compensation or hire. See 61.113(a)

Drop skydivers - No, this would be carrying passengers for compensation or hire. See 61.113(a)

Pull up gliders for pay - Yes. See 61.113(G)

If you're actually planning on flying and making money somehow related to that flying and you aren't 100% sure you are legal, please ask an aviation lawyer in addition to online research.
If even the FAA managed to make a mistake on the subject, there's plenty of room for the rest of us to do so.


Are there any passenger aircraft with no cabin access to/from the cockpit? Most passenger aircraft (airliners and business aircraft) have an internal door or doorway connecting the cockpit area to the main cabin; are there passenger aircraft where there is a solid partition isolating the cockpit from the passenger cabin, and passing between the two requires exiting the aircraft?

Yes, I know that many early passenger aircraft had enclosed cabins with separate, open cockpits; I'm wondering about aircraft with an enclosed cockpit and a separate, enclosed cabin.

The only one I can think of is the Junkers F13. It has an open cockpit and an enclosed 6 passenger cabin. There's no access between the two areas; only a small window.

Credit:THOMAS LÜTHI / RIMOWA 2016

The CEO of Remowa is having recreations made of the aircraft which first flew in 1919. It was (according to Rimowa) the world’s first all-metal commercial aircraft.


What is the best way to give ATC a position report using only a VOR (no DME or GPS)? While cumbersome, is it permissible when asking for a pop-up IFR clearance to state, at the intersection of WWW radial XXX and YYY radial ZZZ?

Obviously, during VMC, you have your pick of visual checkpoints, but in IMC, are there any better suggestions?

Additionally, if you are near a navaid or published intersection, and take a guess at your distance from it, how far off would your guess have to be before ATC wouldn't really even consider it helpful?

I'm going on the assumption you're operating in IMC (or perhaps VMC above a cloud deck) and have no reference to the ground. In a situation if you need a pop-up IFR clearance or ATC is requiring you to provide position reports for some other reason (non-radar, or your transponder is dead and they want to identify you but don't have time to issue you confidence maneuvers).
I'm going to further constrain the scenario with the assumption that all you have are "basic" IFR instruments (6-pack, clock, compass, and VOR -- no VFR/Handheld GPS, DME, or other fancy stuff).

The AIM has some guidance on this subject in 5-3-2, but the general idea is your report should be "as accurate as possible". For routine position reporting like you'd use in non-radar environments (where you're giving an estimate of when you'll reach a reporting point) they're looking for "within 2 minutes flying time" on your estimates in most situations, so you'll want to give your position with the same sort of accuracy.

In the case you describe, with no DME, GPS, or other precision tool for reporting your distance and bearing from a fix your the most accurate option would be to report crossing a published intersection, VOR, or other reporting point noted on your chart - it's the most definite "I am HERE" report you can give, and ATC will certainly know the location.

If that's not an option (ATC needs to know where you are right now, and you're not over a VOR or charted intersection) I would probably start by computing the distance using the intersection of two VOR radials (whether this is a charted intersection doesn't matter, though it would help if your report is relative to one): Break out your chart and mark the location, then take your ruler and measure the distance from one of the stations (or a nearby intersection along the airway you're using) and you've got your position "as accurately as possible".

If you don't have a chart or can't get signal from a second VOR for some reason it's time to work out a time/speed/distance problem in the air:
If you flew over ABC VOR 10 minutes ago and are now flying from the VOR on the 090 radial at 120 knots, and you've got a 20 knot headwind (which you know from the Winds Aloft forecast, updated with data from previous position and time/speed/distance computations) then you know you've traveled about 17 miles, so you're "17 miles from ABC VOR, on the 090 radial".

The time/speed/distance computation has a lot of potential error (winds not as forecast, for one), but sometimes it's your only option.