Are modern airliner avionics spill-proof? I thought about this today, and didn't find much other than a flight decades ago that made an emergency landing due to spillage causing the trim wheel to uncontrollably pitch the plane down into a dive. How spill-proof are avionics today? Especially the centre pedestal? I can't imagine it happens often but it has to happen from time-to-time where a pilot will spill their coffee on the centre pedestal right? It seems like it would be an oversight to not have these be spill-proof.

The actual avionics are down below. The units on the center console are just control heads mostly, although they are still boxes with electronics in them.
In new design these days, there is some effort on the design side to make the units coffee resistant, by using sealed switches and rotary control devices, etc.  But they aren't completely water tight.
The components on the lower center console live a difficult life, getting splashed and kicked regularly by coffee spills and people climbing in and out. On smaller cockpits the sub panels near the bottom of the center console close to the seat get replaced quite a lot from getting kicked.
I participated in a project to approve a new switch design in an audio control panel on the CRJ900, which was right in the coffee target zone, and the switch had to be a water resistant design.
Avionics down below, if they are under the passenger cabin, can also get wet from spills in the cabin that migrate down under the floor.  On the CRJ program, certain black boxes had little rain shields incorporated above them to protect the boxes from getting dripped on.  This is expecially bad for components under the floor near entry and service doors where rain can get in and find its way under the floor and run along floor rails to drip some distance from the original source.


What is the equivalent height of a parachute landing? I understand that this will vary depending upon the equipment used, the bodyweight of the jumper, barometric pressure etc, but what is the approximate equivalent height of landing from a parachute jump? I have heard people say the impact is equal to jumping from 6 feet up onto the ground - and yet I have seen members of the Red Devils land seemingly as easily as stepping off a kerb.

(Mods: I have seen this question which is why I ask here, please relocate to the appropriate SE if off-topic)

As you have intimated in the question, how hard you hit the ground is very dependent on a number of factors.

When I did my training to jump using a classical tethered round chute we practiced landing from a platform of about 5 feet, so six is perhaps a hard landing. That's, roughly, hitting the ground at 12mph.

Folks like the Red Devils typically use an parafoil chute. Basically a self inflating wing. These can be steered and pitched upward to bring the trooper to a stall or even go up if they have enough forward velocity. So yes, you will often see them stop in mid-air and step down. This means this type of parachute has NO equivalent jump height. In fact if flown incorrectly you can crash into the ground at serious speeds.

Regular "military style" parachutes provide no control over lift and only minor control over direction. With these your descent rate is totally dependent on size, weight and air quality.

Interestingly, with a regular chute, what makes landings "harder" is not so much the effective height but the amount of horizontal velocity.

You are trained to drop and roll when you hit the ground to absorb the impact.

This works great if you have any horizontal velocity to help you initiate the roll. If however you are coming straight down it's not so easy.. and your knees end up in your chest...  as I found out the one and only time I jumped out of an aging Cessna.  Too much horizontal velocity and that roll gets rather violent.


Why are there different starter limitations for dry cranking and manual start on the A320? I recently had this point clarified that when we place the mode selector to CRANK on the A320 we can dry crank the engine up to 5 mins. But the moment we place the mode selector to IGN/START then we are limited to 2 mins (I'm mainly referring to the 2 mins with regard to a manual engine start) Could someone please explain why there are these two different limitations?

Per the Airbus maintenance training manual, the crank limit whether it's dry (CRANK) or wet (IGN/START + MAN START) is 2 minutes.

An ECAM warning will notify of exceeding the limit: ENG 1 (2) START FAULT (condition: starter time exceeded).

This video shows the cranking of an A320 jet engine as a test after changing the IDG filter.


How many aircraft types are cabin crew qualified for? I always wonder, how many types of aircrafts can a cabin crewmember be qualified for? is there a limitation by say IATA, FAA or EASA?

I know very little about this, but in the US the regulations appear to say that cabin crew must be qualified by aircraft type and the details are part of the approved training program for each operator (airline).

In the US, 14 CFR Part 121 governs airline operations, and 121.392 says:

  (a) Any person identified by the certificate holder as a flight
  attendant on an aircraft in operations under this part must be trained
  and qualified in accordance with subparts N and O of this part.

Subparts N and O are far too long to quote here (you can always read them yourself), but 121.421 is probably the most relevant regulation to what you're asking:

  §121.421   Flight attendants: Initial and transition ground training.

  (a) Initial and transition ground training for flight attendants must
  include instruction in at least the following:

  (1) General subjects—

  (i) The authority of the pilot in command;

  (ii) Passenger handling, including the procedures to be followed in
  the case of deranged persons or other persons whose conduct might
  jeopardize safety; and

  (iii) Approved crew resource management initial training.

  (2) For each airplane type—

  (i) A general description of the airplane emphasizing physical
  characteristics that may have a bearing on ditching, evacuation, and
  inflight emergency procedures and on other related duties;

  (ii) The use of both the public address system and the means of
  communicating with other flight crewmembers, including emergency means
  in the case of attempted hijacking or other unusual situations; and

  (iii) Proper use of electrical galley equipment and the controls for
  cabin heat and ventilation.

  (b) Initial and transition ground training for flight attendants must
  include a competence check to determine ability to perform assigned
  duties and responsibilities.

  [...]

I couldn't see any limitation on the number of "airplane types" that a flight attendant can be qualified in, but the training is administered by the airline so if there is a limitation it may set by them rather than by the FAA. 121.427 requires recurrent training (but it doesn't say how often) and I assume that at some point a flight attendant who's qualified on multiple aircraft types could end up spending more time training than actually working on flights. That's unlikely to be something that the airline wants to happen.


What are the ASTERIX CAT010 message types 005 and higher? I am analyzing some surface radar recording data under Asterix CAT010 category. The document from Eurocontrol shows that there are 4 standardized message formats under this category:

001 Target Report
002 Start of Update Cycle
003 Periodic Status Message
004 Event-triggered Status Message

However, I could find some other types from 005 to even a few hundred.
May I know what are these message types referring to?

Finally, it is solved. It is not about the data issue but some decoding issue. I am using an asterix-decoder in python from https://github.com/CroatiaControlLtd/asterix.
Based on the help of its author, Damir Salantic. "There was a bug in the presentation of hexdata in case when the old format of asterix is used. Old format has several Data Records in Data Block."
Now the issue is fixed and the decoder repository is updated the decoded data is following the format from Eurocontrol.


Why did the space shuttle use bias-ply tyres instead of radials? Aircraft and automobile tyres can be divided into two main types, based on the orientation of the tyres’ body plies (the layers of tough fabric that form the main structural body of the tyre); radial tyres are built with the body plies laid perpendicular to the bead and tread (so that the body plies extend straight out radially - hence the name - from the tyre bead, straight across from one side to the other at a 90º angle beneath the tread, and straight in radially to the bead on the other side of the tyre), while bias-ply (or simply bias) tyres have the body plies laid at an oblique angle.
Radial tyres are the more common type by far, for very good reason; they are stronger than bias-ply tyres and wear much more slowly.
I was, thus, rather surprised to learn that the tyres used on the space shuttle’s main landing gear were of the older, weaker bias-ply type:

Wheels and Tires
[...]
The main landing gear tires are 44.5 by 21 inches and have 16 cord layers in a bias-ply design. They are normally inflated with nitrogen to a pressure of 370 pounds per square inch (psi). The maximum allowable load per main landing gear tire is 132,000 pounds. With a 60/40 percent tire load distribution, the maximum tire load on a strut is 220,000 pounds. The main gear tires are rated at 225 knots maximum ground speed and have a life of one landing.  [Shuttle Crew Operations Manual; my emphasis.]

The space shuttle’s main landing gear would seem to be one of the worst possible places to use bias-plies instead of radials; with each tyre carrying up to 59.9 tonnes (66 short tons) and having to cope with touchdown speeds in excess of 200 knots, it would seem imperative to use the strongest tyres available.  The magnitude of the stresses placed on these tyres was so great that, while most aircraft tyres can make it through dozens to hundreds of flights before having to be changed, the shuttle MLG tyres were rated for a grand total of one use before replacement.  Additionally, with only four MLG wheels per shuttle orbiter, even a single MLG tyre failure would significantly impair the vehicle’s braking capability, which is most emphatically not a good thing for something going as fast as a landing shuttle orbiter.  Given all this, one would think that radial tyres would be the obvious choice, hands down, for the shuttle’s main landing gear, since their greater strength and slower wear would considerably decrease the chance of a tyre failure upon landing - yet the shuttles instead used bias-ply tyres.  Why?

Simply put, for the weight bearing factor bias-ply is a lighter tire, and when building a spaceship weight is the top concern.

The reason they were thin and single use also had to do with weight, according to NASA:

  Weight: Since weight is of extreme importance, the tires are made with
  a minimum amount of tread to conserve weight, allowing for larger
  payloads. A few pounds may not seem to make much difference, but when
  you add up all of the ways to decrease weight throughout the shuttle
  it can have a significant impact.

When it comes to weight bearing capacity:

  Load-Carrying Capacity

  Advantage: Bias Ply

  Due to their multiple layers, bias ply tires generally have the
  advantage when it comes to load-carrying capacity. Because there are a
  uniform number of plies to support the weight of a vehicle in both the
  tread face and the sidewall, bias ply tires are generally better when
  hauling heavy loads. This is why trailer tires, tractor tires, and
  heavy equipment tires are often bias ply; they can better support
  heavy loads. Radials are available with high load ratings, but the
  weight-carrying capacity requires adding many more plies to a radial
  tire, making them very stiff.

The important line here being "adding many more plies" which will also make the tire heavier (reference above note on weight). It costs in the neighborhood of $10,000 to put 1 lb into space, so if you can save a few pounds on each tire, it does not matter that they cost \$5,660 each; you save by replacing them every time if they are indeed lighter.

  even a single MLG tyre failure would significantly impair the vehicle’s braking capability, which is most emphatically not a good
  thing for something going as fast as a landing shuttle orbiter.

The shuttle has no issue coming to a full stop with a blowout as was the case with the shuttle Discovery in 1985 during the landing of STS-51-D.


What does the message content in the ARINC 615A FIND protocol look like? I know the FIND protocol is used to discover which LRUs are available if the data loader supports the FIND protocol.  I also know the message is sent as a broadcast using UDP, but what is in the message that's being broadcasted?

Attachment 3 of ARINC 615A-3 describes the FIND function. The FIND protocol has an Information Request (IRQ) packet and an Information Answer (IAN) packet. Each packet contains a 2 byte header and a variable length data portion.

  3-4 Information Request Packet

  Source MAC address should be the MAC address of the data loader (or
  the initiator.

  Destination MAC address should be a unicast, multicast, or the
  broadcast MAC address.

  Source IP Address should be the IP address of the Data loader (or the
  initiator).

  Destination IP address should be a unicast, multicast, or a broadcast
  IP address (full broadcast i.e., 255.255.255.255 or class-relevant
  broadcast e.g., 220.130.48.255 for a class C).

  Opcode value should be IRQ (0x0001).

  Data list should be a null ASCII string with terminator: 0x00.

  Packet is terminated by 0x10.


If an Osprey found itself unable to rotate its engines to vertical, what would be the emergency procedure for landing? Let's say an Osprey appears to be flying normally in forward flight. In preparation for landing, the pilot tries to command the engines to begin tilting to vertical, but nothing happens. What now?

If there's a manual way to crank the engines up, that's not working either.

The Bell Helicopter V-22 Guidebook covers survivability in Appendix 1.
Specifically it refers to

Redundant Fly-by-Wire Controls
Redundant Electrical Power
Redundant Hydraulics Swashplate
Actuator Armor

implying that this possibility has been engineered to a minimum.
Nevertheless, the premise of your question is that it's occurred, so further on in the same section we see

V-22 crashworthiness is a function of design. Heavy components,  such
as the engines and transmissions, are located away from  the cabin and
cockpit area. The proprotors are designed to fray or  “broomstraw”
rather than splinter on impact with the ground. The  energy-absorbing
landing gear system is designed to attenuate  most of the energy for
hard landings up to 24 fps. The wing is  constructed to fail outboard
of the wing/fuselage attachment in a  manner that absorbs kinetic
energy and ensures the cabin area will  not be crushed, thereby
protecting the occupants. An anti-plow  bulkhead prevents the nose
from digging in on impact, and the  fuselage provides a reinforced
shell that is designed to maintain 85%  of its volume during a crash.
Aircrew and embarked troops receive  additional protection from
crashworthy seats that stroke vertically to  absorb energy

(my emphasis)
Since the aircraft is still flying, I'd head for the nearest decently equipped airfield, conduct a normal fixed wing approach and land, trusting that the rotors will sweep a nice clean path along the runway instead of peppering the fuselage with shrapnel. I'd probably take the precaution of cutting power early to reduce the kinetic energy in the rotors before they hit the ground.


What type of airspace is an Atlantic Low Control Area? Could someone explain what the blue zipper line 'Atlantic Low Control Area' is in the images below?

What type of airspace is this? How far off the coast does it start? Would it still be G to 1200 and E to 18000 in this area? Is this related to a Warning area which begins 12 NM off the coast? Why are there two parallel lines? I'm not really sure what questions to ask about it but I want to understand it well enough to be able to explain it in a check ride.

The Atlantic Low Control Area is a Class E area in international airspace, where domestic ATC procedures may be used for separation procedures.

Here are the relevant excerpts from FAA Chapter 19. Other Airspace Areas
Section 1. General

  Offshore/Control Airspace Areas are locations designated in international airspace (between the U.S. 12-mile territorial limit and the CTA/FIR boundary, and within areas of domestic radio navigational signal or ATC radar coverage) wherein domestic ATC procedures may be used for separation purposes.

and

  Class A Offshore/Control Airspace Areas are identified as “High" (e.g., Atlantic High; Control 1154H). Class E areas are identified as “Low" (e.g., Gulf of Mexico Low, Control 1141L)

The two parallel lines differentiate floors of class E airspace that is neither 700 feet nor 1200 feet AGL (Above Ground Level).


Why don't airports have weigh stations to prevent overweight takeoffs? Currently, ensuring that an airplane isn't overweight when it takes off relies on the cargo handlers loading the aircraft properly and accurately documenting (on the weight-and-balance sheet) what with how much weight was placed where, and on the pilots properly reviewing the weight-and-balance sheet once the airplane is loaded.  Even then, there are uncertainties (it is rarely possible to know exactly how much each passenger weighs, for instance).  So why don't airports have weigh stations to weigh the planes as they taxi after being loaded, allowing any flights found to be overweight to be ordered back to the terminal to jettison the excess weight?

Aircraft are heavy.

Really, quite heavy.

An Airbus A340, depending on type, has a maximum takeoff weight (MTOW) of up to 380,000 kg.

A Boeing 747, again depending on type, can have a maximum takeoff weight of a shade under 447,700 kg.

Measuring that kind of weight accurately is certainly not impossible, but it's not exactly easy either.

A bigger issue is that it's not as simple as saying that if the aircraft weighs more than some number of kilograms, then it's overweight, and if it weighs less, then all is fine. The distribution of that weight within the aircraft – precisely that "weight and balance calculation" which you mention – matters, sometimes a great deal. The aircraft could be putting an acceptable weight on the wheels, but if the weight is too far forward or too far aft, may still be outside of its controllability limits once it lifts off the ground.

Simply putting the aircraft on a scale and providing the pilots (somehow) with a weight-on-wheels readout as they taxi will catch the situation where the pilot can't add (as in, mathematically add up the weight components that make up the total aircraft weight), but it won't necessarily catch the situation where the load is improperly balanced.

So you'd be adding another fair bit of complexity (which can fail in various ways) to a currently relatively simple part of aviation (the taxiways or apron), possibly giving the pilots a false sense of security, and not solve the problem. Someone would still need to do a weight and balance calculation, at which point the weight-on-wheels reading can, at best, provide a rough sanity check on the weight part of the weight and balance.

Seems easier to just try to figure out ways to make the weight and balance calculations easier to perform, and make random spot checks on weight and balance calculations done (and schedule followup training if the pilots, or ground crew, or whoever else, need it).


Why doesn't the flight path angle increase beyond a certain angle even if the angle of attack is increased? From level flight, when the angle of attack is increased the flight path angle increases (the aircraft starts to climb). What causes the aircraft to stop to increase its angle of climb (angle between the horizon and the speed vector) as I continue increasing AoA at full thrust?
Is the effect described in Paragaraph 1 the same as with steepening the descent at idle thrust when I pull the stick?
Is it right that the critical AoA, above which continuing to pull the stick  causes decreasing speed vector's angle (i.e. "going down instead of up"), is the same for climb and descent and corresponds to $V_X$ (best angle of climb speed) up to negligible corrections?

Thanks
Alex

If you keep increasing your angle of attack, your drag will increase and combined with the increasing along trajectory component (your path angle will increase) of the weight vector will slow you down (assuming your thrust does not exceed your weight + drag). Because you slow down, your lift will decrease. The lift will now be less than the across trajectory component of the weight vector and the flight path will become less steep.
I don't understand your second point.
The critical angle of attack is where the maximum lift coefficient occurs. If you increase the angle of attack further, the wing will stall and the lift will decrease. This does not occur at Vx


Can jet fighter missiles descend or ascend? I am wondering that if missiles fired from jet fighters can ascend or descend?

Are they going to aim only horizontally?

Yes, they can. Air-to-Air or Air-to-Ground missiles are often equipped with little fins that allow certain maneuverability or also with thrust vectoring.

(Image Source: WikiPedia - Author: USAF)

(Image Source: WikiPedia - Author: Titimaster)


Can someone identify this biplane? My grandfather in the back seat apparently.

It is a British Airco DH9A light bomber.

Some more info: According to an RAF database, this particular aircraft with registration E848 served in RAF No. 27 and No. 30 squadrons. Both of these squadrons flew sorties over India and the Middle East after World War I (hence the additional radiator fitted under the fuselage to operate in warmer climates, well spotted by Peter Kämpf), but I can't find anything more specific about E848 that would place it in either squadron in particular at any specific point in history.


Is there a way for passengers to know which runways their flight will use? When I fly, I like to see the airport when I take off and land. Is there a way I can know, in advance, which runway the plane is likely to depart/arrive from so I know which side of the plane to sit in?

No. As far as is reasonably practical, planes land and take off into the wind so the runways that are in use will depend on weather conditions at the time of the flight, as well as traffic and so on.

These things probably won't be known at the time when you're picking your seat.


Where can I find old (historical) FIR map? I'm doing a research with FIR Ho Chi Minh (formerly named FIR Saigon).

I've read a document which said:

During the Fall of Saigon, ICAO, in 28th of April 1975, had divided FIR Saigon into 3 AOR: Bangkok, Singapore and Hongkong, then they gave these AOR to the corresponded FIR.
In the 7th of December, 1994, ICAO sent AOR Bangkok and AOR Singapore back to FIR Ho-Chi-Minh.
In the 1st of November, 2001, ICAO gave part of AOR Hongkong to FIR Ho-Chi-Minh, and created AOR Sanya from the remained part of AOR Hongkong.
In the 8th of June, 2006, ICAO changed AOR Sanya to FIR Sanya

I managed to search those old FIR maps in the internet but no luck for me.

Hence, I would like to find out all historical FIR maps to make a comparison.

If it is impossible to find all FIR maps, old FIR maps of South East Asia FIR is greatly appreciated.

The best I can find is a ATC radar screen used in a dated report (appears to be a report by the Hong Kong Civil Aviation Department in 2000). It shows the FIR regions and waypoints of near Hong Kong, Hainan island and Vietnam:

Here is a dated enroute chart of Hong Kong in 1996. I'm not sure if the waypoint names will be useful for your further search:

How I end up with these: for the first one I used keyword "Sanya AOR". Given the dates you stated in the question, Kai Tak airport was still operational during that time. So I searched for charts of Kai Tak. A full set of charts of the airport would contain an "enroute chart" which lists waypoints. Search engine is Bing.


What is takeoff power? I Am asking about the takeoff power here not how the aircraft takes off.

What do I need if I want to calculate the power required by an aircraft to take off?

What parameters should I consider?

In the physics realm $Power$ = Mass x Acceleration x distance/time

To many it means "how much throttle" , which is how much fuel/time.

"Throttle" x prop efficiency = $Thrust$

This gives you a unit of Force that can be directly compared to glide data as follows:

Potential energy Mass x Gravity x altitude loss = $Thrust$ x horizontal distance flown

This rearranged to $Thrust$ = Mass x Gravity x altitude loss/horizontal distance flown

$Thrust$ = force required for straight and level flight, expressed in "pounds or Newtons"

So if your plane weighs 10 lb and glides 5:1, you need 2 lb of thrust for straight and level flight.

One would at least double, or even triple this for "takeoff power", depending on your performance preferences.  Sufficient "takeoff power" will give a safe climb rate to avoid difficulties with downdrafts.

For example:  my plane glides 5:1 at 60 mph or around 5000 feet/minute and loses 1000 feet/minute.  At 10 lbs it was calculated to need 2 lbs of thrust for straight and level flight.

How much more thrust do we need to climb 500 feet per/minute.  Again, the glide data provides a very good estimate, 2 lbs x 500 fpm/1000 fpm = 1 lb additional or 3 lbs total at 60 mph.  Higher speeds with more drag,  or lower speeds "behind the power curve" will require more than 3 lbs of thrust.


How are unpaved strips created and maintained? I'm under the impression that some large craft are rated for "unpaved strips", which appear to be either some sort of gravel or perhaps dirt.  The 727, and this runway, being a good example of this:

Picture taken from this question, which is also a good reference on how large airplanes can operate on "rough" fields.

What I'm wondering is how these fields are prepared?  I assume the ground is required to be able to hold up a certain amount of weight, and I also assume that ability must be uniform, or you'd be risking a wheel poking into the runway and basically ruining everyones day...

So how do they prepare/create these runways?  And how do they ensure that they maintain the ability to be used for operations with craft that are rated for "unpaved" but probably not rated for "random, somewhat grassy field."

Advisory Circular (AC) 300-004 from Transport Canada has detailed information regarding the maintenance of unpaved runways.

  The purpose of this document is to outline methodologies for the
  measurement and reporting of surface shear strength for unpaved
  runways.  In addition, the document outlines recommended practices for
  condition inspection, maintenance and repair of airport gravel
  surfaces and turf landing strips.

Runways should be designed with consideration for drainage (slope, crown, etc), susceptibility to frost heave, vegetation, roughness, etc.

Maintenance can be based on surface hardness measurements made with a penetrometer. A schedule for periodic inspection is created when the runway is new. The AC recommends a maximum of three years between hardness measurements. One type of penetrometer measurement is described as follows:

  The Boeing High Load Penetrometer (Reference Boeing Document No. D6-24555 - High Load Penetrometer Soil Strength Tester) consists of a hydraulic cylinder with a cone point test probe mounted at the rod end.  The hydraulic cylinder is normally positioned against the frame of a heavy vehicle which serves as a reactive load.  In the test procedure, the probe is driven at a steady rate to a 100 mm (4 inch) depth into the surface by the application of pressure through a hand pump.    Generally a pressure reading is taken about 30 seconds or less after movement of the penetrometer has stopped at the 100 mm (4 inch) depth.

Once maintenance is deemed to be required...

  Gravel pavement surface maintenance primarily involves periodic
  grading to remove the surface irregularities developing with time and
  to re-establish grades for drainage purposes. Occasionally, new gravel
  has to be added to replace lost material.  Dust suppression measures
  may also be needed during the summer months.

The recommended aggregate sizes are shown in this table from the AC:

The recommended grading method is shown here:

Also note a wealth of information in the reference documents listed in section 2.1 of the AC.

This presentation (.pdf link) from a company that provides airport maintenance services has additionl useful information and photos.


What is Auto-thrust? I have heard about auto-thrust yet I still don't know what it is. Can someone please explain to me what it is?

I know that I can just Google this up, but I was hoping that a community which revolves around aviation would be able to answer my question.

I did end up using Google to do some preliminary research and I found this definition:

  An autothrottle (automatic throttle) allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling the fuel flow.

In its basic form, it is just like the cruise control in a car.*

Here is a photo of the autopilot control panel on a Boeing 777. Note the "IAS 200" window on the left:

IAS stands for "indicated airspeed". When engaged, this setting tells the auto-thrust to adjust engine power to maintain 200 knots of airspeed.

Just like a car, when you go uphill you need more gas to maintain a constant speed, and when you go downhill you give it less gas. If the downhill is steep enough, you may have to use some brakes to maintain a constant speed.

Same thing happens when a plane pitches up to climb or pitches down to descend. Airspeed, vertical speed and engine power are closely related - changing any one will impact the remaining two. This is the fundamental of how planes fly, and likely your first ground school lesson if you learn to become a pilot. Auto-thrust is a component of the autopilot system which manages engine power. Note that I used constant airspeed as an example in the previous paragraph: advanced autopilots have many modes, and it can be set to maintain constant vertical speed instead of airspeed. But in all cases, auto-thrust manages engine power.

* Well said TomMcW


Where is the compression on a compression strut in a tube and fabric airplane coming from? I understand the functions of every part of a tube and fabric (two spar) ultralight wings and the loads they carry but what keeps puzzling me is the compression strut of a two spar wing as seen above.
My question is where is this compression on a compression strut between the main and rear spar coming from? Is it from the drag and anti wires, the spars itself, where and how do you calculate this conpression force?

You want a nice, taut fabric cover on this wing, don't you?

The main function of the compression struts is to keep both spar tubes from being pulled closer by the fabric cover. Of course, Niels is right, aerodynamic forces come on top of this and will also pull on the tubes in the wing's plane.

In order to calculate those forces, integrate the tension in the fabric over wingspan when loaded by maximum lift forces. Below I have sketched those lift forces – they want to pull the fabric up, increasing tension within it and so the compression forces on the struts.

I hope I got the basic structure about right. Please correct me where needed.


How do airports determine when they should change their runway numbers? Runway numbers in most of the world are based on the runway's orientation relative to magnetic north.  For example a runway with a magnetic heading of 135° to 144° will be numbered 14, and one with a magnetic heading of 145° to 154° will be numbered 15.
Runway numbers are occasionally changed due to changes in the Earth's magnetic field.

At my home field Runway 14/32 is oriented 145.7°/325.7°, per the FAA's airport diagram, and it has been this way for some time (I first recall noticing it over a year ago).
My understanding is that this runway should, at some point, be renumbered 15/33.

How does the FAA determine when to request that an airport change its runway numbers?
Is the decision to update the runway designation made by the FAA, or by the airport's management?

Implementing changes to runway numbers is quite complicated and requires a lot of different parties to get involved.  There is a ton of related information in FAA Order 8260.19E and it has the details.
Simple Version
According to an article by the NBAA called "How Changes in Magnetic North Are Impacting Airports":

“Adjustments to runways like this and to navigational aids are
ongoing,” according the Kathleen Bergen, a spokeswoman for the FAA
Southern Region. “Every five years, the FAA reevaluates shifts in the
pole—its magnetic variation—and makes changes to runways and flight
procedures as needed,” she said.

Medium Version
NOAA, NOS, and NGS (see below) provide the magnetic variation information, and publish it every five years.  They work with a bunch of different offices, and different branches of the military as they make adjustments.  When a determination is made that a runway number should be changed, they coordinate with several other groups (such as AeroNav Products, OSG-FPT, the applicable Airportt Traffic Service Area Office, and the Airports Division), to choose the actual number used, based on "careful consideration and evaluation of a number of factors" and then to make the actual changes in charting, runway markings and signs, etc.
They are supposed to change it when it is more than three degrees off from what it is should to be.  AC 150/5340-1L - Standards for Airport Markings contains the official runway designator rules (paraphrased):  If the actual magnetic course of the runway ends in 5, it can use either number, otherwise you round to the closest runway number (there are some variations for special cases like parallel runways and such, but this covers most runways). So in your example, 145 is still valid as runway 14, and they wouldn't need to change it until it exceeds 148 deg.  In your case, the annual rate of change for Farmingdale airport (as of 2010) is 0.0 deg East, so I don't see that happening for awhile.
Long Version - Quotes from FAA Order 8260.19E (above)

Section 5. Implementing Epoch Year Magnetic Variation (MV)
a. Background. The National Oceanic and Atmospheric Administration
(NOAA), National Ocean Service (NOS), and the National Geodetic
Survey (NGS), for all areas of the United States and its territories
for application to navigation charts and maps, is the source for
magnetic variation (MV) information and tools for establishing
magnetic variation. Changing values for MV are tabulated and published on
a 5-year epoch basis; e.g., 00, 05, 10, 15, 20, etc. In order to
assist in stabilizing the National Airspace System (NAS), a fixed
value of MV is assigned to each  navigational aid and airport as the
Magnetic Variation of Record. This value is applied to true
directions to obtain the magnetic values for radials, courses,
bearings, and headings published in instrument flight procedures.
Periodic updating of the MV assigned to navigation facilities is
required to maintain reasonable proximity of alignment with the
earth’s ever-changing magnetic field. ...
b.
Participating Offices. Management and control of Epoch Year MV values
require action  by the following offices:
(1) AeroNav Products.
(2) Military Organizations.
(3) National Flight Data Center (NFDC).
(4) Western, Central, and Eastern Technical Operations.
(5) Western, Central, and Eastern OSG-FPTs.
(6) Regional Airports Divisions.
...
f. Regional Airports Division/Airports District Office (ADO).
Coordinate with the  applicable OSG-FPT prior to establishing or
revising runway designator numbers for an airport  having one or more
instrument approach or departure procedures, to determine the
appropriate MV to be applied to the runway true bearing. Determination
of the runway designator number should be a matter of joint agreement
with AeroNav Products, and be accomplished sufficiently in advance to
allow for procedural amendments. Take appropriate NOTAM action if
repainting of an affected runway has not been accomplished on the
required date.
...
2-18. Guidelines. The identification and selection of navigational
aids or airports as candidates for revision of MV of Record require
careful consideration and evaluation of a number of factors - as the
impact of MV changes can be considerable. The applicable Air Traffic
Service Area Office may have to initiate or revise published air
traffic procedures; the Technical Operations Service (AJW-0) is
directly involved in facility rotations and requires proper
coordination. The Airports Division, or appropriate military
authority, may have to arrange for repainting of runway designator
numbers [see paragraph 8-58e(2)(e)].
a. MV versus Epoch Year Value. When the difference between the MV of
Record and the nearest future Epoch Year value of any navigational aid
or airport is 3 degrees or more, the MV of Record must be changed to
the nearest future Epoch Year value.


What is the temperature of the brakes after a typical landing? On an airliner, what is the temperature of the brakes after a typical landing, and how long does it take to cool down?

Is it hot enough that mechanics should wait before servicing an aircraft that has just touched down minutes before?

Judging by this IATA document, and looking at figure 4 in section 4.2.1, the brake temperature easily exceeds 700°C during landing. They also show some brake temperature history timeline for an airplane without fan cooling.

(Figure 4)


How to calculate aileron deflection for achieving similar roll dynamics at thin and dense air? my question is inspired by projects like Perlan etc when one is trying to fly in thin air with a glider.
It is well known that at high altitude (say 10-20km) aircraft control becomes 'sluggish'.
However, thinking about lift equation I have encountered a paradox.

According to https://en.wikipedia.org/wiki/Lift_(force)

Lift coefficient is
L=const x rho_air x true_airspeed^2 x surface_area x coefficient_of_lift

Let's neglect the fact that at high altitude, with Reynolds number changing, one will get into a diferent CL (coefficient_of_lift)  vs AOA curve. This is a small issue compared to span of possible rho_air values.
Because this equation has true_airspeed^2, it is obvious that at low altitude, aileron effectiveness (which is also a lifting surface) will raise with second power when increasing TAS which at normal atmospheric conditions and low altitude, low subsonic speeds equals to EAS and CAS (IAS).
If we take any glider and lift it up, rho_air will decrease even by factor of 16 for simplicity. This will be compensated by required TAS forward glide speed by factor of 4, so that wings can still provide equal lifting force, otherwise tha plane would fall because of winning F=m*g - which doesn't care about air composition. The plane will fly faster, and while we should expect that diminished rho_air would diminish aileron effectiveness, increased TAS will naturally compensate for this following the same equation...

I have concluded that starting to roll which requires applying non-opposed rolling force to overcome (constant!) airplane inertia, so that roll rate will rise until it becomes balanced by wing drag resistance, should require identical aileron deflection for airplane at low and high altitude. In other words achievable rates of change of roll rate should be the same at cruise speed in thin air when using the same aileron deflection.

At high altitude however, measured IAS and CAS will be much lower than TAS but that doesn't matters as stable airplane will balance by itself at cruise speed.

Then we come into question what is the maximum roll rate achieved in thin vs dense air. After applying aileron deflection the roll rate will increase, when applied rolling force is compeensated by aircraft drag due to rollign motion whcih is again proportional to constrho_airrollrate^2.

I have concluded that maximum achievable rollrate will be higher at thin air, using the same deflection of ailerons that provide the same overall rollign force at high altitude because the airplame must fly faster just to provide its lift. With the same aileron deflection, achieved stable state roll rates will be higher in thin air than at dense air with the same aileron deflection

If all above is true, why airplanes are said to be 'sluggish at high altitudes due to thin air'.

Your conclusions are correct; however, it is new to me that aircraft control becomes "sluggish" at high altitude. Only when you fly up into the coffin corner will control effectivity suffer since you fly close to stall, but that is very similar to the diminishing control effectiveness when you approach stall at lower altitude.

To express your conclusions in the way it can be found in flight mechanics books:

Roll acceleration does not change with altitude because it is dominated by aileron control power and roll inertia, and
The final roll rate will change inversely with the square root of air density because here the roll damping of the wing comes in which is inversely proportional to airspeed.


How do dummy bombs simulate real bombs in training when they're so much smaller? This picture shows a couple of Mk-76 25lb (11kg) Inert Training Bombs on a McDonnell Douglas AV-8B Harrier II; it's clear that the physical characteristics of the dummy bomb are quite different to actual munitions.

source

The manufacturer says these bombs are "used to simulate the MK-82 in low drag configuration". The venerable Mk-82 is typically 500 lb (227 kg): here's an F-16 with Mk-82s for scale comparison:

source

One obvious advantage of the smaller, lighter bombs is that they're vastly cheaper to operate, both in terms of handling on the ground and the amount of fuel you'd be using in the air. However, the dummy bomb is 20 times less massive than the bomb its designed to simulate: its small size and weight surely mean their aerodynamic characteristics are very different to the bombs they're supposed to be simulating. (I know that speed of fall in a vacuum is not dependent on weight, but a falling object in air is affected by shape, weight, drag etc.)

My question is - since their purpose is presumably to help train the pilots, how can tiny dummy bombs usefully simulate real bombs?

The actual mass alone is nearly irrelevant to its a trajectory - what mostly matters is the mass/drag ratio - so if you scale the drag correctly, it feels quite the same - at least from the operational point of view. As one does not drop bombs by sight only, a small adjustment on the computer will do the other trick.


What is the maximum takeoff weight allowed for a part 103 ultralight? What is the max takeoff weight (MTOW) for a part 103 vertical takeoff (VTOL) ultralight?

And is the value peak or continuous limit?

14 CFR 103.1

The FAA currently does not discriminate between "VTOL" and "normal" ultralight aircraft, nor between gas-powered or electric. The aircraft, if powered, cannot weigh more than 254lbs "empty" weight excluding floats and safety equipment that deploys in an emergency situation.

I'm not sure what you mean by "peak limit" or "continuous operation". The aircraft, when weighed without liquid fuel, must be less than 254lbs. It can carry up to 5 US-gallons of fuel (which can add up to 30lbs).

There is no limit to the MTOW for the aircraft though, it can carry a 400lb individual if you can make it fly, but it can't carry more than 1 person. So if the aircraft weighed 253lbs, you were 400, fuel is 30 that is 683lbs and still legal under Part 103. (Depending on how liberally you want to apply the "single occupant" rule, you may try to squeak your 200lb Mastiff aboard as well)


When do commercial flights turn off the APU? On commercial flights do the pilots ever turn off the APU? Is it needed when flying?

This varies due to operational need and airline standard operating procedures.

On my aircraft (an Embraer E-Jet) we turn on the APU roughly ten minutes prior to pushback and shut it down shortly after starting the engines.

If we plan on taxiing on one engine we will shut it down after the first engine start and perform a cross-bleed start on the second engine. Other operators leave the APU running for second engine start.

If performance requirements demand the engine bleed to be off for takeoff we will leave the APU on until after takeoff to provide cabin pressurization until the engine bleeds come back online.

We typically leave the APU off for the remainder of the flight and do not turn it back on until the next flight, unless ground power is unavailable or unreliable at the destination, in which case we will turn it on after landing as we approach the gate.

The APU can also be left on (or started in flight) to assist with various abnormal or emergency situations where bleed air or electrical power generation might be needed. Each APU installation will have a different flight envelope in which it can be started / used and is specified in the aircraft's operational limitations.


What is the procedure to enter, maintain and recover from a flat spin? Looking for a play-by-play from the pilot's seat of a Pitts biplane. What thoughts, considerations and control inputs are required to enter & maintain a flat "pretty" spin and a calculated exit path?

Visual example:
What is going on in this guy's head, his hands and his feet?

If I remember from flying the Pitts S-2B, entry into an inverted flat spin was fairly easy, starting from an entry in the vertical, similar to performing a hammerhead stall, but using a excess of rudder with insufficient aileron pressure.  Another method is the fly a Lomcovak, which inevitably terminates in an inverted flat spin.

Again, it all depends on the edge of the envelop characteristics of the aircraft in question.  And some aircraft may not be recoverable at all once a flat spin is entered.  With aircraft certified to fly this kind of an aerobatic maneuver, recovery is fairly simple with motions being countered with rudder and elevator pressure.


Why are we still putting lead in our fuel? Lead in gasoline for automobiles has been banned from nearly every corner of the world, with most bans dating from the nineties. Why are we still poisoning ourselves with lead in Avgas? I understand that Tetraethyllead (as it's apparently technically called) is an octane booster, but the Wikipedia article also mentions that advances in the production of high octane unleaded fuel have pretty much nullified that argument. There are more reasons of course, but none the automotive industry wasn't unable to overcome many decades ago. I know it's 'low-lead' with very little lead compared to 'traditional' gasoline, but the phase-out of leaded fuels in cars started back in the 1970s, so don't tell me that most aircraft are simply too old. Are aircraft engines so special compared to car engines, that they must get their fix of lead before they go flying?

It is also a fact that there are aircraft piston engines which do run perfectly fine on unleaded fuel, why is it that hardly any airport offers it? Even in cost-conscious and eco-friendly Europe, most airports offer only 100LL and Jet fuel.

There is nothing "special" about an aircraft engine that requires lead in the fuel -- Engines don't much care about the lead in tetraethyl lead, nor do they much care for it (it gets everywhere, fouling sparkplugs and contaminating the oil). What they care about is the octane (anti-knock) rating of the fuel.

Many "low performance" aircraft engines run just fine on unleaded fuels with a lower octane rating (among them the Lycoming O-320 and O-360 family that power a good chunk of the GA fleet), but high-performance aircraft engines (e.g. the IO-520 you'll find in Beech Bonanzas) require a 100 octane fuel. The approved specification for 100 octane aviation gasoline (ASTM D910) lists tetraethyl lead as the octane booster of choice.

It's also worth noting that some of the octane boosting techniques used in automotive gasoline are not acceptable for aircraft engines (the most common in the US being the addition of ethanol, which has two undesirable effects: reducing the energy content of the fuel, and damaging aviation fuel system seals and other components).

So why do we still make 100LL, and why don't we offer the other unleaded options at every airport?

Aviation gasoline is a minuscule slice of the gasoline market, so it doesn't make sense to have 5 tanks with 5 different grades of fuel at every airport:
All aircraft engines will run on 100LL, so 100LL (leaded) aviation gasoline is still produced because it is a "single fuel" solution to piston aviation's needs.

If leaded avgas were to disappear tomorrow the engines that require it would be left without an approved fuel, which would result in those aircraft being grounded until such time as an alternative fuel could be developed or the engine manufacturers develop a procedure for derating the engines (operating them at reduced power). For obvious reasons neither of these options is attractive, particularly to folks who own higher-power engines which were presumably purchased for the performance...

Changing the avgas specification is quite a bit of work - it requires ensuring that the new fuel is a "drop-in replacement" for 100LL -- one which can be mixed with 100LL in any proportion, and will work correctly in any engine designed for 100LL fuel.
The FAA is working with engine manufacturers and major fuel producers on a program which will result in such a specification (a Google search for unleaded avgas transition also produces useful results), and hopefully a universal unleaded aviation fuel specification and one or more products will come out of those efforts.


When to use feeder route The following section is from Instrument Procedures Handbook (FAA):

If a feeder route to an IAF begins at a fix located along the route of
flight prior to reaching the holding fix, and clearance for an
approach is issued, a pilot should commence the approach via the
published feeder route. For example, the aircraft would not be
expected to overfly the feeder route and return to it. The pilot is
expected to commence the approach in a similar manner at the IAF, if
the IAF for the procedure is located along the route of flight to the
holding fix.
If a route of flight directly to the IAF is desired, it should be so
stated by the controller with phraseology to include the words
“direct,” “proceed direct,” or a similar phrase that the pilot can
interpret without question. When a pilot is uncertain of the
clearance, ATC should be queried immediately as to what route of
flight is preferred.

Can you give examples to clarify it  a little bit more for each case. Pictures are appreciated.

I found your quoted text in Section 5-4-6 of the AIM. You quote paragraphs b and c of the section. I will break down paragraphs a, b, and c using examples. Each paragraph is discussing a situation in which a pilot has been cleared to a holding fix (perhaps by clearance delivery, i.e. the last fix in the flight plan) and has been "cleared ... approach" prior to reaching that fix.
Paragraph 5-4-6 a

An aircraft which has been cleared to a holding fix and subsequently “cleared . . . approach” has not received new routing. Even though clearance for the approach may have been issued prior to the aircraft reaching the holding fix, ATC would expect the pilot to proceed via the holding fix (his/her last assigned route), and the feeder route associated with that fix (if a feeder route is published on the approach chart) to the initial approach fix (IAF) to commence the approach.

Summary: What to do when there is a feeder route from the holding fix to the IAF.
For example, prior to departure, a pilot calls clearance delivery and receives clearance to KMOB via V198 BROOKLEY VOR. They plan to shoot the ILS 15. Here is the approach plate and the chart.

Notice the feeder route from BROOKLEY to the IAF. If the pilot is "cleared ... approach" while on V198 transiting to BROOKLEY, their route has not changed. They must proceed to BROOKLEY as cleared, and then use the feeder from BROOKLEY to CAYAT (IAF). They may not turn directly to CAYAT unless specifically cleared to do so.

Paragraph 5-4-6 b

If a feeder route to an IAF begins at a fix located along the route of flight prior to reaching the holding fix, and clearance for an approach is issued, a pilot should commence the approach via the published feeder route; i.e., the aircraft would not be expected to overfly the feeder route and return to it. The pilot is expected to commence the approach in a similar manner at the IAF, if the IAF for the procedure is located along the route of flight to the holding fix.

Discusses: What to do when there is a feeder route from a fix on the route of flight prior to the holding fix.
In this example, a pilot plans to fly northbound to KMGM. They call clearance delivery and receive clearance to KMGM via V222 MONTGOMERY VOR. They plan to shoot the ILS 10.

Notice there is a feeder route from ALOON. If the pilot is on V222 heading north toward ALOON when they receive clearance for the approach, they will be expected to use the feeder from ALOON instead of overflying ALOON and proceeding all the way to MONTGOMERY VORTAC. In this case there is a feeder route from the holding fix as well, but that may not always be the case.

Paragraph 5-4-6 c

If a route of flight directly to the initial approach fix is desired, it should be so stated by the controller with phraseology to include the words “direct . . .,” “proceed direct” or a similar phrase which the pilot can interpret without question. When uncertain of the clearance, immediately query ATC as to what route of flight is desired.

Summary: If a pilot would like to fly directly to an IAF without using a feeder route, they can request to do so. The clearance must contain the specified phraseology.


Is there a website that shows past flight tracks of a few days back? I'm looking for a website, like Flight Radar, that can display the positions of aircraft going back a few days (i.e. not a live map)

If you just need a few days then FlightAware let’s you do that. I think it goes back 7 days for free. Past that you have to pay. That is for a particular flight. FR24 has a history feature that will play back the whole radar starting at a particular time. It plays back at 12x speed, though.

On FR24 you just open the main screen, move the map where you want it then click the clock icon on the right side. Enter the time and date you’re interested in. Note that it’s in UTC time, so you’ll have to convert your local time to UTC.

Then it will begin playing back. You can see the time and playback speed on a bar at the bottom of the screen.


Is this a very sloppy holding pattern or something else? This scheduled Belavia service to Barcelona appears to be in a very sloppy holding pattern where they aren't correcting for wind at all. Is it normal for a passenger jet to fly like this?

It does indeed look like they are not correcting for wind. The current wind over Belarus at 10km altitude looks like this:

(screenshot from windy.com)
That is consistent with the direction in which they are drifting. Such a flight path is not a normal holding pattern, which is based on a holding fix. While wind might push the aircraft somewhat off the nominal racetrack pattern, they would at least regularly overfly this fix (although modern RNAV systems are pretty good at compensating for wind).
I can only speculate on why they are flying like this. Most likely they are not holding at a specified fix. They might have been instructed to hold at current position by ATC, probably while they figure out if they are still allowed to fly into the EU, after the European Council has called for a ban:

The European Council:

[...] calls on the Council to adopt the necessary measures to ban overflight of EU airspace by Belarusian airlines and prevent access to EU airports of flights operated by such airlines;

(europa.eu)

Update: It seems they are returning now:

(flightradar24.com)


Why do airports have directional runways instead of a large area to operate in any direction? Instead of a few runways in a few directions, why not have a large square block of asphalt so that planes can take off and land in any direction? Where and on what direction planes land and take off will still be determined by ATC, but these decisions are then not bound by the choice of just a few runways. So, there will only be virtual runways and taxiways instead of real physical ones.

The typical World War II "A" runway shape solves this issue, without covering a huge amount of area with concrete, etc. Even so, that configuration has fallen out of use in modern airports.

Ultimately, this is a solution to a problem that doesn't really exist and a problem which has a more efficient solution that was already widely used.

With respect to your particular question - to some degree, this is exactly how original grass fields were treated. But no matter how convenient, there's always a need for consistency and predictability and you can see how that has developed to what we have now. Taxiing a heavy airliner isn't a trivial task - doing so with no markings or defined route sounds terrifying.

Additional practical issues of your large slab of concrete vs. a defined runway:

No ILS
No runway lighting
No runway markings
No threshold, no touchdown markers
Far more difficult to precisely define runway length
Very very difficult to accurately describe a particular location and route

To be honest, the list goes on and on and I'd struggle to imagine commercial ops being able to operate like this safely and efficiently.


Is the air in a jet engine supercritical? Nitrogen has a critical point of 126.2 K and 3.4 MPa (34 bar). Air contains 75 % of nitrogen

  For example, nitrogen has a critical point of 126.2 K (−147 °C) and 3.4 MPa (34 bar).

source : https://en.wikipedia.org/wiki/Supercritical_fluid

In a jet engine pressures often exceed 34 bar ( as seen on Wikipedia, where for example the GE9X is shown to reach 60 times ambient pressure ), the critical temperature of nitrogen is exceeded at room temperature. So is air ( fluid ) in the high pressure regions of a jet engine supercritical ?

Maybe at takeoff, definitely not in cruise

You have to consider that atmospheric pressure drops with altitude. At FL360 you have ~0.226 bars. Even multiplying with the GE9X's pressure ratio of 60, you get ~13.56 bars, well below the 34 bars needed.

Takeoff might be a different situation, since the engines are operating at full power with ambient pressure ~1 bar, this could lead the high pressure compressor stages to operate in supercritical conditions. Note though that the combustion that immediately follows changes significantly the chemical composition, and thus the critical point might be altered as a consequence.

As engines are optimized for cruise conditions, it is highly unlikely that supercritical conditions have extensive design consequences, unless they would render takeoff impractical.


What are these teardrop shaped thingamabobs on the bottom of the Panavia Tornado? What are these two teardrop shaped thingamabobs on the bottom of the Panavia tornado?

They could be hardpoints but I haven't found any photos where anything would have been mounted there. They don't look like hatches. And they don't seem to be any kind of vortex generators either. What purpose do they serve?

Click to view full-sized image:

Here's a few closer images:

They appear to be related to changing the oil.

The Tornado's flight manual is available online. Page 448 shows what seem to be the features you're talking about:

The features are the ones marked as "12." The previous page has a legend describing them simply as "engine oil."

This probably also explains why they're not placed symmetrically. It seems the engine oil access is off to the side, so each teardrop is a bit to the right of the engine's center line (that's most visible in the second picture).


In track while scan mode of radar operation what are the methods to predict next position of target? In a track while scan system (TWS) the algorithm states that the processor predicts the next position of the target and compares it with the actual position but what are the actual methods of prediction?

Standard approach for radar tracking is as follows:

Prediction of next position using one Interacting Multiple Model per aircraft. The basic model is made from two Kalman Filters, one of which predicts constant velocity (in 3D), the other predicts a constant-rate turn (also in 3D). The model selects the prediction from the filter that performed better during the last few updates.
Data from the scan arrives. Positions of the blips are compared to the predicted positions and the Joint Probabilistic Data Association technique is used to associate each blip with one of the tracked aircraft. If there are unassigned blips, a new model is set up to track the newly discovered aircraft.
Each aircraft's model is updated with the associated blip's position. This includes updating each Kalman Filter as well as selecting which of the filters should be used for the next prediction (the one that predicted the current blip more accurately).


What happens when a pilot is incapacitated? Is there a contingency for such a situation, where one of the pilots leaves the cockpit, the other pilot is incapacitated (for example losing consciousness) while the first pilot is still outside the cockpit and can not reenter the cockpit. If there is not, is that not a huge flaw, as multiple pilots are meant as a redundancy.

Edit: This is in my opinion not a duplicate of this question, since the big problem in my question is the door to the cockpit being only openable from the outside.

In the linked question, the answer is simply "both pilots being incapacitated at the same time is highly unlikely". The scenario I described is not highly unlikely. One of two pilots being incapacitated is not improbable and the door to the cockpit is only openable from the inside.

So if one pilot is incapacitated while being temporarily alone in the cockpit, the other pilot is "automatically" locked out of the cockpit.

Is there a contingency for such a situation, where one of the pilots leaves the cockpit, the other pilot is incapacitated (for example losing consciousness) while the first pilot is still outside the cockpit and can not reenter the cockpit.

Yes, a keypad on the door will allow the second pilot back into the cockpit. It doesn't help when the pilot outside doesn't know/forgets the code or if the unlock code is denied from inside the cockpit.


What is this aircraft from "Devil Girl From Mars" (1954)? This view is cropped from the opening seconds of the film Devil Girl From Mars. Within the film narrative, this one was supposedly carrying passengers over the Scottish Highlands in the then-present-day, which turns out to be 1954.

If you can help me with the type, I can find most of the other information I need by myself.  However, I would also be interested to know

(a) whether there is anything to be discovered from the barely-visible markings, and
(b) if it's possible to tell whether this shot represents a particular model of the type in question, and what that might say about the background of this specific machine (regardless of context in the film).

It's a Vickers VC.1 Viking in the livery of British European Airways (BEA).

(By RuthAS (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons)


Can a US registered motorglider be flown in Canadian airspace when piloted by a pilot with the appropriate FAA glider license? Is a PPL-Glider recognized as ICAO approved? Can a US registered motorglider be flown in Canadian airspace (or land at an appropriate Canadian airport) when piloted by a pilot with the appropriate FAA glider license? (NOT an add on to a PPL SEL)

Unless your license says on its face that it doesn't meet ICAO requirements (as FAA student, sport and recreational licenses do), then when you are flying an aircraft registered in that same ICAO member state, that state's licensing rules apply and all other states must accept it as valid regardless of their own rules.

So, in your example, if the FAA says your aircraft is a "glider" and you have a private glider license, then you're legal in Canada even if, for instance, Transport Canada thinks your aircraft is an "airplane" and would require an airplane license for their own pilots to fly it.


What does the runway distance mean under "Additional Runway Information" on Jeppesen plates? See my previous question

What are Runway Declared Distances?

On Jeppesen 10-9 or 10-9A charts, there is a section dealing with Additional Runway Information.  Does these distances correspond to the declared distances in the A/FD?

From page AIRPORT-3 (page 3 overall) of this Jeppesen legend (site jump-off page here):


What aircraft has the highest suggested landing speed? Just out of vague curiosity, what aircraft has the highest recommended landing speed for an earth bound (atmospheric) craft?  And, btw, when I say "landing" I define it as thus:

Controlled
Powered (though if you want to note unpowered, feel free)
Safe, with the vehicle/aircraft fully recoverable
On a runway
On wheels or skids

I know there may be multiple answers, even with my trying to narrow it down, so feel free to list a few different scenarios.  I'm mostly wondering about planes that are in common usage though, both military and civilian (past and present)...  I'd have to think something like the SR-71 or MIG-25 would be very close to the top of the list, if not the top.

Based on its fixed-wing hypersonic design and inordinately high wing loading, I would predict that the X-15 has the highest recommend landing speed of any earthbound aircraft, with a preliminary search seemingly bearing this hypothesis out. According to an ostensibly legitimate NASA source (link below), the X-15's normal landing speed was 200+mph (173.8kts=321.9kph),

http://www.nasa.gov/centers/armstrong/news/FactSheets/FS-052-DFRC.html

But if unofficial sources are to be believed, its actual landing speed was much higher, closer to 390kph=208kts (although these numbers are admittedly more dubious):

  “According to an early edition of 'the Guinness book of world records' the X15 also holds the record for fastest landing speed at 242 mph compared with 210 mph for the space shuttle.”

http://area51specialprojects.com/x15.html

If only powered aircraft are open to consideration, then the F-104 Starfighter would have to be up there as well. It needed a blown-flap flow control system just to be sane during landing...

  “To make landing speeds “reasonable,” The F-104 forced engine air through the wings to smooth the airflow and give more lift. With bleed air, the Zipper could land at the challenging but not extreme speed of 160 to 165 knots. If the air-bleed system was not working, landing speeds climbed to 240 knots.”

http://www.pacificaviationmuseum.org/pearl-harbor-blog/lockheed-f-104-starfighter

So, if mechanical failure scenarios are deemed admissible, then the F-104 without its crucial boundary layer control systems would be the clear winner for powered landing speed, weighing in at an absolutely terrifying 240 kts. Otherwise, it would appear that the X-15 (unofficially) reigns supreme.


What is the difference between company routes and pilot routes? I was trying to find out what are the different route types(flight management system) and found out there is one company route and one pilot route . Are there more different route types ?.What is the difference between the company route and pilot route

A company route, or coroute, is just an easy way for the pilots to download the flight planned route into the FMC, without having to enter every route segment manually. It saves a bit of time, especially on longer routes, and eliminates the risk of input errors.

I haven't heard the term "pilot route" before, but presumably it just means the lack of a company route - i.e. a route that the pilots have entered manually.

Functionally, once the route has been entered in the FMC, there is no difference between a company route and a route entered manually. The only difference between the two is the way they are entered.


Are landing fees due for an aborted landing in USA? Suppose I receive landing clearance for an airport that charges a landing fee, and begin my decent. Then, for some reason I have to abort the landing and instead of going around and landing there I change my plans and wish to depart the airspace. Will I be liable for any landing fees if my wheels haven’t touched the runway at such airport?

I am asking for GA in the USA.

I commuted to work in my plane into an airport with a landing fee for a few years (I was doing it frequently enough that I paid for an annual subscription with unlimited landings). In Canada you won't be charged if you go around and I can't imagine being charged in the US either.  Although ATC records the landing, the fee is usually levied by the airport authority and is intended to cover airport services, not ATC services.


What are the advantages/disadvantages of placing an engine in the tail? What are the advantages and disadvantages of having an engine in the vertical stabilizer, a la the DC-10, Lockheed TriStar, and 727?

It seems that this has gone out of fashion among jetliners. Is there a reason for this?

It seems that the FAA's 60 Minute Rule was an impetus for the trijet configuration. But is that the only motivation? Is a tail engine less aerodynamically efficient?

As you write, at the time those trijets were designed they enjoyed preferential treatment over aircraft with two engines for overwater operation. They also were more efficient than comparable designs with four engines. See here for that discussion.

However, the wing-mounted engine has some advantages:

Flutter damping when mounted ahead of the elastic line of the wing
Bending relief
Easier access for maintenance
Shorter fuel lines

The tail position was chosen because three engines were enough for the optimum size of those airliners and equipping them with four engines had lowered efficiency. If you need to put three engines on an aircraft, one has to be in the line of symmetry, and here the best compromise was on or in the rear fuselage. Had more powerful and reliable engines been available back then, you can be sure they would had used only two engines and mounted them on the wing. But we had to wait two more decades until turbofan engines were powerful enough and the certification authorities were convinced of their reliability.

The fashion of early jets to put all engines at the back was just that and had ended before the trijets were designed.


What will air traffic controllers do when radio contact is lost? When a pilot loses radio contact with ATC, there are standard procedures to follow, e.g. squawk 7600, observe the traffic pattern, observe the red / green light gun.

On the other side, if a controller attempts to contact an aircraft and gets no response, what will they do? Assume that radar contact is not lost, or the controller is not equipped with radar.

EDIT: Let say a controller spotted a 7600. What's next?

You didn't mention any specific jurisdiction but for the FAA, the expected actions are in the ATC orders. Section 5-2-8 says:

  When you observe a  Code 7600  display, apply the procedures in para
  10−4− 4, Communications Failure

Section 10-4-4 gives general instructions for comms failure, it's too long to quote in full but the first paragraph summarizes it:

  In the event of lost communications with an aircraft under your
  control jurisdiction use all appropriate means available to
  reestablish communications  with the aircraft. These may include, but
  not be limited to, emergency frequencies, NAVAIDs that are equipped
  with voice  capability, FSS,  Aeronautical Radio Incorporated (ARINC),
  etc.

The instructions suggest some specific actions:

Broadcast via NAVAID frequencies
Ask the aircraft to use its transponder or make turns to acknowledge instructions

If comms haven't been reestablished within 5 minutes, ATC is instructed to consider it as suspicious:

  If radio communications have not been (re) established  with the
  aircraft after 5 minutes, consider the aircraft’s or pilot’s activity
  to be suspicious and report it to the FLM/CIC per FAA Order JO 7610.4,
  Chapter 7, Hijacked/Suspicious Aircraft Reporting and Procedures

Section 10-2-5 also says that lost comms are an emergency from the ATC perspective and should be escalated to the ARTCC. If comms aren't restored within 30 minutes then the aircraft is considered overdue, which triggers another set of procedures listed in section 10-3.

As for clearing airspace or whatever, there are no specific instructions in the orders, it just says that:

  When an IFR aircraft experiences two-way radio communications failure,
  air traffic control is based on anticipated pilot actions.

In other words, ATC expects IFR pilots to follow lost comms procedures as per 14 CFR 91.185 and will direct other traffic accordingly.

Finally, one 'routine' lost comms scenario is when ATC can't contact an aircraft because of poor radio coverage. This happens a lot with smaller aircraft (which fly relatively low) operating in remote areas and ATC might ask another aircraft, usually a higher-flying airliner if possible, to contact the first aircraft and relay their call: N12345, this is BigAir 123 with relay from Denver Center.


What is the minimum allowed altitude for helicopters over a residential area in the US? I observed a helicopter hovering over a residential area/houses for more than 20-30 minutes. I would guesstimate about 500 feet altitude or more for the helicopter. The low altitude and long duration of the hovering created lots of what I would call unpleasant "noise pollution".

What is the FAA minimum allowed altitude for helicopters over a residential area?

re "possible duplicate":

@fooot I already googled and read that entire question. That question is asking about "when is a Helicopter legally allowed by FAA to fly below the FAA's minimum allowed safe altitude?" and that question is even more specific to a specific situation observed by the OP. They both have wording that talks about minimum altitude but are not the same question.

As others have noted in the comments, they agree this is not a duplicate.

It depends on where it is.
A residential area/houses may or not be "congested" -- that term is not defined. But we typically use 500 feet for helis.
When hovering in an area for a specific purpose, such as photo shoots or other surveillance operation, or for some other operational reason, then we can use a lower altitude.

Sec. 91.119
Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an
aircraft below the following altitudes:
(a) Anywhere. An altitude
allowing, if a power unit fails, an emergency landing without undue
hazard to persons or property on the surface.
(b) Over congested
areas. Over any congested area of a city, town, or settlement, or over
any open air assembly of persons, an altitude of 1,000 feet above the
highest obstacle within a horizontal radius of 2,000 feet of the
aircraft.
(c) Over other than congested areas. An altitude of 500 feet
above the surface, except over open water or sparsely populated areas.
In those cases, the aircraft may not be operated closer than 500 feet
to any person, vessel, vehicle, or structure.
(d) Helicopters,
powered parachutes, and weight-shift-control aircraft. If the
operation is conducted without hazard to persons or property on the
surface--
(1) A helicopter may be operated at less than the minimums
prescribed in paragraph (b) or (c) of this section, provided each
person operating the helicopter complies with any routes or altitudes
specifically prescribed for helicopters by the FAA; and
(2) A powered
parachute or weight-shift-control aircraft may be operated at less
than the minimums prescribed in paragraph (c) of this section.]


Why must one wait 48 hours to fly, after scuba diving? Is this rule even true and why is it? I'm going to assume it has to do with pressure but can someone give me a good explanation?

Yes It's true. And yes it's related to pressure.

Have you heard of "The bends" or decompression sickness?

As divers go deeper the pressure increases. The longer you dive and deeper you go the more nitrogen is absorbed into your blood as a dissolved gas. As you return to the surface the pressure reduces and the nitrogen reverts to a gas.

This decompression needs to be done slowly so the nitrogen can pass back out through your lungs.  If you ascend too fast the nitrogen can form bubbles in your blood (Just like when you open a bottle of coke.) which can be painful and possibly fatal.

Even once you have finished diving you will still have residual nitrogen in your blood which will take time to release.

Air pressure reduces further when you fly. If you finished a dive and got in a plane the rapid climb in altitude would result in a drop in pressure similar to a rapid ascent while diving. So you would run the risk of getting the bends.

Small planes aren't pressurized. But even pressurized planes might not maintain atmospheric pressure when flying.

This topic should have been covered if you have taken a dive course.


Is there employment opportunities of becoming a pilot I am 18 years old and I want to become a pilot so bad .i got B grades in math and C grades in physics and geography.but my parents don't want me to be one since is hard to get employment of becoming a pilot.So am asking is there any employment opportunities of becoming a pilot

By the time you get your Commercial checkout (or ATP) or what ever your local jurisdiction requires you should have no issues finding a job just based on the numbers. There is a growing shortage of pilots and its no secret there are jobs available:

Pilot Shortage Is Real and Getting Worse
The pilot shortage
Cargo Airlines face pilot shortages
A 'Perfect Storm' Pilot Shortage Threatens Global Aviation


How did ww1 pilots handle G-forces? The wikipedia page on G-forces, https://en.wikipedia.org/wiki/G-force, lists that WW1 aircraft encountered 4.5-7g during dogfights.

This made me wonder, how did pilots in the early days of aviation handle the g-forces? G-suits were not invented until 1940s.

This interesting British document on the G loads sustainable by German WW1 fighters pegs the highest G factor for a British fighter at 5.5G for reference, with the SE5. German fighters examined and tested by the British after the war didn't fare quite as well, with max G tending to be in the 2-3 G range, beyond which the rear wing spar would fail.

What is also important to consider is that WW1 aircraft on both sides were not capable of sustaining those G's for very long, due to the low airspeed and rather underpowered engines of that day. An aircraft sustaining very high G's bleeds off quite a bit of speed in the process, due to the increased drag.

A WW2 fighter capable of 300-350 knots with a 1500-2000 hp engine, can pull a lot of g's for a long time, before scrubbing off enough speed to be in danger. A WW1 fighter at 80 knots, with a 150-200 hp engine, would only be able to sustain high G's for a few seconds, before they lost enough airspeed to risk stalling.

The few motion pictures of dogfights of that era, presumably re-enacted, tend to reinforce this: the planes appear to make a series of brief sharp turns interspersed with returns to level or near level flight, sort of a jerky movement as opposed to the long high G turns of WW2 fighters.

Finally, there were techniques some pilots used to avoid blacking out. Major Greg Boyington, who had been a boxer before the war, reported withstanding more G's longer by tightening his neck muscles up.


Portable radio for cockpit communication I am a private pilot based at Van Nuys airport in Los Angeles. Recently due to traffic congestion we have to hold short for extended periods of time, 20-25 minutes.
I thought to get a portable radio to be able to turn the airplane engine and master switches off and save on the rental fee and the constant breaking.
Any recommendations about the specifications of a say 5-10 nautical mile range portable radio is appreciated.

Buy a portable, handheld transceiver. It can very well come in handy in an emergency. Especially one with GPS, VOR, and ILS. Make sure you get a headset adapter with it.
Do not use it to save money during a long hold-short request. Turning the engine off after you have done your run up is not recommended. It is defeating the purpose of the run up. A better technique is to get your flight following discrete squawk code and/or clearance delivery electronically, by phone, or by handheld before turning on the Master and engine.


Are taxiways numbered in a predictable order? When taxiing at an airport without a full-blown airport diagram (most commonly, a non-towered airport), how does a pilot know whether taxiway A (Alpha) is on one end of a runway, or the other? Or, in the case of taxiway exits, how does one know whether exit A1 is at one end of a runway, or the other?

In other words, are taxiways numbered in a predictable or consistent way? An example would be, “Exit A1 is always located at the easternmost exitway of Alpha”. If they are, is this because of custom or regulation?

In the U.S., taxiway number/nomenclature is generally designed in accordance with FAA AC 150/5340-18F. Also, Engineering Brief 89 available here clarifies some of the information in the AC with respect to taxiway numbering/nomenclature. The two pages shown below summarize the guidelines for numbering (from Engineering Brief 89)

Also, note the general taxiway numbering/nomenclature schema for Los Angeles International Airport (KLAX) illustrated on the bottom of this page.  The letter "A" starts the taxiway nomenclature beginning on the south side of the airport and progresses alphabetically towards the northside of the airport.  Intersecting taxiways are numbered sequentially.

Airport taxiway nomenclature can be very complex depending on the airport.  Also, as modifications are made to the ramps and movement areas, etc., effectively designating taxi routes or other areas of the airport becomes challenging.

Finally, in the U.S., there is a taxiway numbering/nomenclature methodology that is framed within FAA guidance documents.  A close comparison of the design guidance with current airport layouts and taxiway numbering/nomenclature not only illustrates the complexity involved but also reveals, in most cases, a consistency that can be relied upon and proves to be extremely useful in actual practice.

Excerpt from Engineering Brief 89 (two pages):


How does new media streaming technology equate to fuel cost increase? In regards to this article on BBC, which discusses the use of streaming technology to allow passengers to watch films/TV shows etc. on their portable devices, the following statement caught my eye:

  It would increase the drag of our aircraft by 2%, which equates to 20
  million euros [$23.6m; £15.5m] in extra fuel.

Is this cost increase purely to do with an increase in weight and additional drag owing to the new equipment required or is there any other factors at play here?

Because it says "drag", my guess is that implies an external antenna.
For example (which I found using a Google search),

Commercial and Large VIP Aircraft Broadband Internet Solutions
HR6400 Antenna System
The HR6400 antenna system for commercial and large VIP aircraft
provides passengers and crew true wireless broadband Internet access.
No matter where you fly - over land or water in any region of the
world - you can browse the Internet, send and receive emails in
real-time, use Voice-Over-IP (VoIP) telephony, access your VPN,
conduct video conferencing, and watch IP television.
The emerging standard for Ku-band systems with the most efficient
Ku-band antenna available, the HR6400 is mounted on the aircraft's
fuselage, providing all the performance you need in the smallest
possible footprint. The easy-to-install HR6400 comes complete with
antenna, antenna control unit, high power transceiver, radome, and
radome attachment ring. It covers everything from the energy coming
from the satellite to the modem connection.

For example, here is a typical antenna installation (not necessarily the one mentioned above) on a 737:


What's exact offset degree dividing localizer and LDA? When a localizer is offset at an angle with the runway track, it functions as a "Localizer Directional Aid or LDA." What's the exact offset degree dividing them? Any offset degree greater than 0 makes a localizer an LDA? I've checked various sources including AIM, but none of them gives me a definite answer.

The maximum angular offset for a LOC is 3° for FAA and 5° for ICAO. Everything else is named either LDA (FAA) or IGS (ICAO).

In ICAO wording, any ILS which doesn't meet all ILS requirements is an instrument guidance system (IGS).
Localizer type directional aid (LDA) is a designation used by FAA.

Guidance /aid refers to the fact that this system is not a precision approach, only an assistance for for the approach.

The most infamous IGS (at least for sim users) is probably the one used at Kai Tak RWY 13 until the airport was decommissioned. Current ones include Sion LSGS RWY 25 which terminates before the runway (see also Washington KDCA RWY 19 as commented by @Gerry), Innsbruck LOWI with a 5° offset localizer or Lugano LSGS RWY 01 for its 6.6° glideslope.

Many of those non-standard approaches are required to access an aerodrome at the bottom of a valley. All require special training and certification before a pilot is authorized to use them.

ICAO defines approach characteristics in Doc 8168 Procedures for Air Navigation Services (PANS-OPS), volume II: Construction of Visual and Instrument Flight Procedures. According to SKYbrary (Eurocontrol) "PANS-OPS procedures are the international standard and are used throughout Europe and in many other countries world-wide".
FAA equivalent are the United States Standard for Terminal Instrument Procedures (TERPS, Order 8260.3). According to the same source: TERPS are used by "USA and certain other countries. These include Canada, Korea, Saudi Arabia and Taiwan".

ICAO PANS-OPS

Final approach segment:

  (5.2.1) When runway aligned track guidance is not possible it may be
  offset up to 5 degrees without OCA/H penalty (see 5.4.3.1, “Aligned
  straight-in approach”). Beyond these limits (or where other
  requirements cannot be met) a circling approach shall be used.

ILS Cat I:

  (2.1.1) The localizer course line shall intersect the runway extended
  centre line:

  a) at an angle not exceeding 5°; and b) at a point where the nominal
  glide path reaches a height of at least 55 m (180 ft) above threshold.
  This is called intercept height.

  (2.1.2) The procedure shall be annotated: “localizer offset ...
  degrees” (tenth of degrees). The general arrangement is shown in
  Figure II-1-2-1.

FAA TERPS

Localizer without glide path. Final Segment alignment (8-1-2):

  Localizers aligned within three degrees of the RCL are identified as
  localizers. If the alignment exceeds 3 degrees, they will be
  identified as LDA facilities.

Localizer with glide path (ILS). Final segment alignment (10-2-2 a):

  Where a unique operational requirement indicates a need to offset the
  course  from RCL, the offset must not exceed three degrees. The offset
  course must intersect the runway centerline at a point 1100 to 1200
  feet inside the DA point (see figure 10-2-2 ). For offset courses the
  minimum HAT is 250 feet and the minimum RVR is 2400.

For LDA with GS (10-2-2 b):

  The final course maximum offset from RCL extended is 15 degrees. The
  final course must cross the RCL extended at least 3000 feet from LTP,
  but no more than 5200 feet from LTP.


Did Airbus bring back LAF (Load Alleviation Function) on A320s with Sharklets? I have heard that the A320 no longer has LAF (Load Alleviation Function) except for really old ones, but I also heard that A320s with Sharkelts do have LAF. So is it true that Airbus got rid of LAF on A320s and implemented it back on A320s with Sharklets, if so does anybody know why, because I heard Airbus says they go rid of it because it was not needed, so why would they add it back if they did? I heard it has something to do with that it increases MTOW (Maxium Takeoff Wight).

LAF is a function that alleviates load on wings roots, but was causing early wear to the actuators and to ailerons and spoilers hinges.

No LAF is not available on latest A320’s


Approach plate does not require DME, but DME used in the published missed? This approach plate doesn't say "DME REQUIRED", but the published missed approach uses DME.

Can I still fly it without DME equipment?

If this approach didn't say "RADAR REQUIRED", could you fly it without being in contact with ATC, and how would you manage the DME in the missed?

DME can be used in the published missed, but does not have to be. There are other ways to identify the missed approach fix.

The missed approach instructions are:

  MISSED APPROACH: Climb to 1500 then climbing right turn to 3500 on ATL VORTAC R-005 to TROYS INT/ATL 15 DME and hold.

The missed approach procedure calls for a hold at the TROYS intersection. This can be identified by one of three means:

The intersection of the ATL R-005 and RMG R-115,
By 15 DME on the ATL R-005, or
By RNAV from a database.

These multiple methods of identification mean that DME is not required. If an RNAV or dual VOR receivers are used, DME is not needed.


What is this Airbus A320 passager seat part? I'm on a Airbus A320 anyone have any idea what the black part on the back of the passager seat is used for?

That’s a credit card reader so a passenger can purchase either premium food products or spirits or inflight entertainment items.


Is the Bendix/King KMD-550 airplane icon always oriented to the north? I have a 2001 Cessna 182T with King avionics. The KMD-550 moving map display correctly shows "track up" but the little airplane icon is always pointed to the north.

How can I set this so that it points track up as well, or is there some kind of fault with the unit?

According to the Source:

  The bottom is for the icon in track up mode. For the North up mode, It
  Depends on the Heading. The fix icon should be placed on one of the 8
  positions (up left, up right, up center, bottom left, bottom right,
  bottom center). For example, if the Heading is 45°, the fix icon is
  placed on the bottom left part of the screen.


What is it like to volunteer with Civil Air Patrol (CAP) as a pilot? I saw various people talking about volunteering with CAP. I’m about to sit my test for my PPL, and am wondering whether there are opportunities to volunteer for search and rescue, or more generally, am interested to hear what is involved.

(I’m in the San Francisco Bay area, if anyone has specific local content as well.)

There are almost always opportunities to volunteer. However, joining CAP is a larger commitment than simply saying "I'd like to volunteer to fly." You will need to attend regular meetings and perform non-pilot duties such has becoming an administrative officer or participating in recruiting and fund raising activities. For some squadrons, the budgets are tight, and the ratio of pilots to flights can be high. The complaint I heard from CAP members back in Idaho was that they hardly ever got to fly. This may be less true in other areas.

My suggestion to you would be to contact your local squadron. In your case, this will be a squadron within the California Group 2 (San Francisco Bay). They have senior squadrons located in Palo Alto, Oakland, San Jose and elsewhere (senior squadrons are for adults 18+, whereas cadet squadrons are for children under 21. There are also composite squadrons for both seniors and cadets). Talk to them about their mission and what the experience would be like. If you're still interested, attend some meetings (you'll need to do this before they'll let you apply anyway). Then, after you have a good sense of what will be expected, if you believe in their mission, and you're willing to put in the time required, you should join.

If all you're looking for is a way to build cheap (or free) flight hours as a private pilot, then that is probably the wrong reason to join, and you will likely be disappointed.

*Note from editor: The oddity in the ages of membership for the senior and the cadet groups should be explained. A person may join as a cadet in a squadron up to their eighteenth birthday, however, if they became a cadet before that, they may continue as such until their twenty-first birthday. Anyone joining the Civil Air Patrol after eighteen enters into the senior branch.


Do helicopter rotor tips regularly go supersonic? In my question about helicopter noise, I made the assumption that one reason they are so darn noisy is that the main rotor tips go faster than the speed of sound. @FreeMan questioned whether that was the case.

I've tried to find information about this but most pages end up discussing VNE -- the forward speed at which the advancing blades go supersonic while the retreating blades lose lift and stall. This is not about that situation.

This is about regular flight -- is the extremely loud noise from helicopters because their rotor tips are supersonic, or is from other sources?

p.s. There is some mention that the "WOP-WOP" of descending helicopters is caused by the rotor tips going supersonic. Is this the case - and if so, is it an edge case (the only time the tips are supersonic) or just one example of when they do.

The "wop wop", usually known as blade slap, is heard when the tip of the blade passes through the vortex created by the previous one.

It can be avoided.  The most common flight regime when this happens is a shallow descent but still with quite a lot of power - e.g. fast and shallow.  The vortex starts to move down as soon as it leaves the tip of the blade so in level flight, the following blade passes over it.  In a shallow descent with high pitch angle, the following blade can literally "slap" into the previous vortex.  The vortices of the two blades now interact and can cause local, transient supersonic flow.  To avoid it, simply lower the pitch to establish a more positive descent or pull back on the cyclic to increase disc loading and flatten the attitude.

The blade tips do not go supersonic.  In fact, in nearly all helicopter designs, the rotor rotates within a very narrow range of speeds, typically between 90% and 110% of the normal speed.  In most flight regimes, the rotor is rotating at 100%, +/- a few percent, whether you are climbing, descending or cruising.  Only during auto-rotation and aggressive manoeuvring does the range vary by 10% or more.  It depends on the type of helicopter but absolute limits would be something like 85% (panic time, risk of complete stall) and 115% (smaller panic, risk of damage to the machine, especially in the tail rotor drive shaft).

In normal operations, and design aims to achieve this, the rotor tips do not go supersonic since when they do, there is a sudden and large decrease in performance with more power required, higher blade loads, vibration and noise.

Think about a helicopter flying forwards.  The advancing blade at its most perpendicular position experiences a relative airflow which is equal (ignoring all kinds of minor side effects) to the forward speed plus the speed of the blade.  The retreating blade is experiencing a relative airflow equal to the speed of the blade minus the speed of the helicopter.

If the blades rotate so fast that the tips are supersonic, then the main lift generating part of the retreating blade, the outer two thirds of the span, would experience such a low airspeed, for some of the span it will even be negative, that the blades will stall causing a catastrophic roll into that side.  It is this phenomenon which ultimately limits the rotational speed of the blades and the maximum speed of the helicopter.

Let's look at the R22 as an example.  The following figures are approximate.

The rotor tip speed is about 670 fps (feet per second).  The speed of sound at ground level on a standard day is about 1100 fps.  The R22 is flying at close to VNE, let's say 100kts which is about 170 fps.

The tip on the advancing side, at it's fastest, is therefore flying relative to the airflow at 840 fps and on the retreating side, at it's slowest, at 500 fps.

The blade length is about 11 feet, so the middle portion of the blade on the retreating side is only flying at 190 fps (half of 670 minus the airspeed).  When you get to about 4 feet out from the blade root, it's now only 50 fps and not much further in from that, becomes zero, then negative.

Remember that lift is proportional to the square of the speed.  You can now see the huge discrepancy between lift on either side as airspeed increases.

To answer your question directly, the R22 would need to fly at 530 fps to approach supersonic tip speed which equates to about 330 kts which it can't get anywhere near achieving.

PS.  The R22 POH speaks in Imperial measures.  When I get some time, I'll redo the figures in metric which I, and most of the world, prefer.