Can you file an open-ended IFR flight plan? Say you are doing an instrument training flight with a CFII and you are practicing IFR navigation. You will be taking off and returning to the same airport, but you are not certain exactly where your CFII might have you go. For instance, your CFII wants to see how you handle deviations in flight. Ths is just an example as I'm sure there are other reasons one would need to be IFR without a specific routing or destination. How would you file such a flight plan? Can you file an IFR flight plan without a specific routing?

Another reason I can think of would be a test or acceptance flight that needs to be conducted in class A airspace. You would have to be on an IFR plan to fly there, but your ultimate destination would be right back where you came from. You might not be able to indicate specific waypoints, etc., instead you would be requesting block altitudes, etc. if you need room to perform maneuvers.

If operating within a single area (TRACON) then file from KABC -> KABC and in remarks put "Practice APCHS KXYZ KDEF".  The controller will be asking you what your next approach will be at some point.
Another tactic is to file to ABC VOR (or some other fix) and request a hold. I like this method, as the student gets a hold with an EFC and that gives me time to decide how many orbits they will need as well as the next approach request. I normally have the student ask for the next approach, as it keeps their workload up.
The first suggestion is generally preferred because in the event of lost com, in a true IMC environment, it is clear that you will be returning to KABC, unless you encounter VFR first.
Remember that an IFR clearance can end at a fix (even a pilot defined fix) and when you are in VMC that can be useful. Similarly, an IFR clearance can begin at a fix, and that can be accomplished in a non-radar environment.
Addendum #1
Frequently this type of plan is often referred to as a tower clearance, or if it spans TRACONs it may be called a tower-to-tower.  However, where there are no local approach facilities, center handles this type of clearance as well. Other than just normal approach practice, an area clearance is used to permit photographic missions with cloud cover and instrument student experience with lake effect icing.  For example, a photographer wanted photos of a water fall, through an opening in the clouds.  We got on top, stayed IFR, and maneuvered for his shots.


How do I tell a Garmin 430 not to exit a hold? Let's say that we're directly west of CATLI and have been cleared direct CATLI for the RNAV approach.  We load the approach into the GNS430 and proceed direct the fix.

After crossing CATLI outbound for the hold-in-lieu-of-procedure-turn, we realize that we want to stay in the hold for a few more turns.  How do I tell the 430 that I don't want it to sequence to ZAMGI upon arrival at CATLI?

Press the OBS button to put waypoint sequencing into suspend, as indicated by the green "SUSP" appearing over the OBS button.


Why don't modern F-16s incorporate the VISTA thrust vectoring? Modern incarnations of the F-16, such as the Block 70/72, F-16I and F-16IQ appear to incorporate many modern technologies. These aircraft are also rather different from the original F-16A, being heavier and more of an all-round fighter than a dedicated air superiority aircraft.

With heavy wing loading and a heavier aircraft overall, why was it considered to drop incorporating thrust vectoring into the F-16, to retain more of its dogfighting capability? This is hardly new technology to the F-16, considering the VISTA first flew in 1992.

This appears especially interesting considering highly maneuverable opponents such as the emerging J-20, Su-57; but also older fourth generation aircraft. The Typhoon, Rafale, Su-37, J-10, and others, are all roughly in the same ballpark as the more modern (heavier) F-16s, correct me if I'm wrong.

Does this indicate that dogfighting is a thing of the past? How can this be, considering that the F-22 was designed to be supermaneuverable? This appears to be a contradiction to me.

Thrust vectoring adds weight, cost and complexity, and the benefit isn't important enough to outweigh that.

Various aircraft have been used to experiment with thrust vectoring, but the list of thrust vectoring fighters in service is fairly short:

F-22
Su-30 (newer variants)
Su-35S
J-20 (fairly new)
Su-57 (very new)

The F-16 was envisioned to be a small, light, and cheap fighter. It has certainly grown heavier and more expensive over the years, but that is still one of the big selling points. Although it worked fine for the VISTA experiments, the limited space, power and cooling on the F-16 is best used for other upgrades, such as better sensors. And the F-16 is still selling fairly well. Lockheed is still getting enough orders that they moved the production line to make room for the F-35 rather than shutting it down.

Even the F-35A, intended to replace the F-16, adds stealth but not thrust vectoring. If you can kill your adversary before they even know you're there, dogfighting ability becomes less important. There's also the reality that US manufacturers build primarily for the US, and for US interests. There might be resistance to exporting an even more maneuverable F-16 when it may already be close in capability to the F-35.


Why are airspaces depicted in AGL? Generally we fly under the rule of QNH which means our IA is above mean sea level. And as we all know airpace limits are charted in MSL. Then, why the definitions of airspaces are they (class C, D and E) depiceted in AGL?

You're confusing the airspace height with airspace altitude.

The definition of Class C (in the US) is

  3-2-4 (a) Generally, that airspace from the surface to 4,000 feet
  above the airport elevation (charted in MSL)

If you look at chart for the Class C for Colorado Springs (elevation 6,187), the surface area of the airspace goes up to 10,200 ft MSL, approximately 4,000ft above the airport elevation of 6187.


What happens if full thrust is applied at cruise altitude for 5-10 minutes on a 787? What happens when you apply full throttle to the engines of a Boeing 787 at cruise altitude for 5-10 minutes?

Other than wasting fuel, what maximum speeds are reached?

Does that pose any danger or damage to the airframe?

Autopilot flying straight and level

Upon reaching the VMO/MMO the A/P will be inhibited from trimming down any further, which will result in the airplane climbing at the VMO/MMO.

  Overspeed protection limits the speed to which the airplane can be trimmed. At VMO/MMO, the trim reference speed is limited by inhibiting trim in the nose down direction.

Hand flying straight and level

Pushing the thrust levers forward will result in a climb at the current speed due to the fly-by-wire design—only the trim buttons change the "trim reference speed".

  Once the column forces are trimmed to zero, the airplane maintains a constant speed with no column inputs. Thrust changes result in a relatively constant indicated airspeed climb or descent.

Source: Boeing 787 FCOM chapters 4 and 9.

Further reading:

What does the term "trimming" most commonly mean in aviation?
Why does overspeed cause structural damage or failure when limit load factors are not exceeded?
How does envelope protection work in Airbus vs. Boeing aircraft?
How does auto-trim work on fly-by-wire aircraft?


Can an airplane engine fire be extinguished without shutting down the engine? Airplane engines catch fire from time to time (and are falsely reported as being on fire even more often).  In a modern airliner, the "fire handle" shuts down the engine, closes the fuel pipe, and discharges the fire extinguisher.

Occasionally it's desirable to leave the burning engine running because you need the added thrust. For example during WWII B-29 engines had an unfortunate habit of catching fire on takeoff. Standard procedure was to leave the burning engine running until you got enough altitude to safely discard the bomb load and/or bail out.

Is it possible to activate the fire extinguisher without shutting down the engine?

In most modern jets (e.g. Boeing 757/767) when you pull the fire handle the engine shuts down (fuel, hydraulic, etc., are cutoff). But pulling the fire handle only "arms" the extinguishing system.  You have to rotate the handle (left or right) to discharge a bottle. (there are other bottle configurations based on the airplane type, but this is the general scheme)

Usually, after pulling the fire handle (before rotating it left or right) you wait momentarily to determine if the overheat or fire warning lights have extinguished.  If not, you rotate the handle to discharge the extinguisher.

So, if you are asking about modern jets, the answer would be no, you can't discharge the extinguishing agent without shutting down the engine first.

I am not aware of a modern design that would allow the engine to continue operating after activating the fire extinguishing system.


What is the difference between a nautical mile and a statute mile? And what is a knot? What is the difference between a "nautical mile" and a "statute mile?"

And what is a "knot?"

According to the Encyclopedia Britannica a nautical mile used to be based on the curvature of the earth and was approximately equal to one minute (arc segment) of latitude along a meridian (longitudinal line running from north to south). The British nautical mile was set to 6,080 feet while the US nautical mile was set to 6080.20 feet. However, in 1929 the nautical mile was redefined to exactly 1.852 km (approximately 6076.11549 feet) at an international conference held in Monaco, although the US didn't make the conversion until 1954.

1 nautical mile = 1.1508 statute miles or 1.852 km.

A "knot" (speed measurement, not the kind you tie in your shoe laces) is equal to one nautical mile per hour.

1 knot = 1.15 miles per hour.


Why was there a rattling noise coming from the left engine of A319? I recently flew on an Airbus A319. When boarding the aircraft from the front entrance we passed in front of the left engine. The fan blades were spinning and there was a rattling noise (like when a chain is being rolled up) coming from the engine.

Is this normal? What causes this sound? Is it the fan blades that are somehow loose?

Yes indeed, the fan blades are loose and rattle in their sockets when the fan is freewheeling in the wind. Once the engine is running, centrifugal forces will make sure they do not rattle any longer.

The base of the fan blades have a shape like a fir tree, and they slide into sockets on the fan disk with a loose fit. When the fan is spinning slowly, they will sit on one side of the socket on the way up, and gravity will pull them into the opposite side on the way down. The rattling is caused by one blade after another falling into that opposite position once they rotate over the top.

Sorry for the bad picture (source) - I could not find a better one right now.

There are concepts to move to bladed disks ("blisks"), but while they are lighter and don't rattle, they are a headache once a single blade is damaged and needs to be replaced. Therefore, the single, easily removable fan blades are the solution of choice in all gas turbines.


Have I made a calculation mistake in this ATPL question that uses the CAP 698 Chart? I have been calculating this question but I just don't seem to get the correct answer.
For this question use Performance Manual CAP 698 SEP1 Figure 2.3.
Using the climb performance chart, for the single-engine aeroplane, determine the   ground distance to reach a height of 2000 ft in the following conditions:

Given:
OAT at take-off: 25°C
Airport pressure altitude: 1000 ft
Aeroplane mass: 3600 lb
Speed: 100 KIAS
Wind component: 15 kt Headwind

My Workings
*TAS = 104kt (from using CRP-5)
GS = 104kts - 15kts = 89kts*
Climb Gradient = 10.7% (from chart)
Still Air Distance = (2000 / 10.7) X 100 = 18,691ft
Ground Distance = 18691 X (89/104) = 15,995ft

But the CAE Oxford ATPL says that 16,850ft is the answer.
The next closest answer is 15,750ft which is what I would choose.
Please help me out here, thank you in advance!

Reference:
CAE Oxford ATPL Chapter 8, Question 4.

The relevant section (3.2.3) of CAP 698 explains how to calculate this as follows:

Distance to Reach given height.
To calculate the ground distance travelled in order to attain a given height above
reference zero:
a) Convert the IAS 100 kt to a TAS, assume no position error.
b) Apply the wind component to the TAS to obtain the ground speed.
c) Determine the climb gradient from the graph.
d) Calculate the still air distance using the formula:
$$\text{Still Air Distance} (ft) = \frac{\text{Height Difference} (ft)}{\text{Gradient}} \times 100$$
e) Calculate ground distance using the formula:
$$\text{Ground Distance} = \text{Still Air Distance} \times \frac{\text{Groundspeed}}{\text{TAS}}$$

Assuming your calculation of TAS is right, and your interpretation of the graph is right (which I agree with) you can plug this into the above calculations and confirm the answer is indeed:
Ground Distance = 15,995ft
However, if we play devil's advocate and reverse engineer the climb gradient from the expected answer, you'll see there might be some human/interpretation error at work.
Taking the published answer of 16,850ft and dividing by $\frac{\text{Groundspeed}}{\text{TAS}}$ gives us a ground distance of 19,690ft. Take this and Divide by 100 gives 196.9. Then doing $\frac{1}{196.9} \times \text{Height Difference} (ft)$ gives a resulting climb gradient of 10.2 - this is all just mathematics, no aviation knowledge required.
Now, can you say for sure that you've not misread/misused the chart? Once again I got the same result as you by looking at it in low def on a screen. But it's possible we both miscalculated the climb gradient.

Side note: I see question like this come up fairly regularly on other aviation forums, and a reasonable amount of time it is student error and a reasonable amount of time it is publication error. Make of that what you will.


Is the separation distance between two aircraft approaching an airport the same under CDA and Non-CDA scenario? I'm working on a project that investigates Continuous Descent Approach (CDA), the procedure by which an aircraft approaches an airport for landing by descending continuously from cruise altitude with idle or near-idle thrust setting. As a Continuous Descent Operation (CDO), CDA provides operational benefits in terms of fuel burn reduction which reduces emissions as well as noise levels around airports.

In my project, I'm studying CDA operations during high traffic periods with the aim of developing key performance indicators (KPIs) for airports. However, I really need some expert and professional advice from pilots and air traffic controllers (ATC) on how CDA is being coordinated, managed, and conducted between pilots and ATCs. The following questions underscore my point:

If a pair of jet aircraft is approaching an airport, is the separation distance between them smaller, the same, or larger under CDA and Non-CDA scenarios?
Just before touchdown on runway, is the aircraft's approach speed the same under CDA and Non-CDA scenarios?
In general, how many track miles could be used for approaching traffic at a major airport?
In general, is the airspeed during descent different between CDA and Non-CDA scenarios?
Just before touchdown, will the pilot utilize thrust to increase speed or will the aircraft be on its own volition, under CDA and Non-CDA scenarios?

Continuous descent operations do not warrant a change in separation minima. The same separation minima (wake turbulence, radar minima, lateral, horizontal and vertical minima) apply at CDA airports as they do at all other airports.

To answer 2, 4 and 5 at the same time: continuous descent approach means that an aicraft descending from cruise level (typically 10-11 km.) to the final approach procedure (typically about 1000 metres) will do so in one continuous motion - e.g. without levelling out and maintaining a certain intermediate level along the way.
Although it is possible, and widely utilised, crews are not required to use idle engine thrust for the descend. It may well be the case that an aircraft is required by air traffic control to maintain a certain speed during descend, in order to establish and maintain the separation requirements mentioned above. As such, you can see CDA operations where aircraft apply thrust during descend, but where the descend is still conducted as one continuous motion.
On the final approach, usually starting at an altitude of about 1000 metres, 20 or-so km. from the airport, there is no difference between CDA and non-CDA operations. Aircraft will fly completely normally, using engine thrust and lift augmentation devices (flaps, slats) to maintain an appropriate airspeed (actually, angle of attack) so that the aircraft descends at the correct rate to hit the runway. For a normal jet aircraft, it is not possible to fly the final 20-or-so km. of the approach with idle thrust - it simply wouldn't make it to the runway.

When talking about track miles, I will assume you are talking about the distane from the top of descend (TOD) until the runway threshold (THR). For an average jet airlines, descending from a level of 10-11 km., it will take somewhere between 100 and 120 nautical miles of distance to get from TOD to runway THR. For non-CDA airports, this distance will generally be longer, because the descend has to be initiated sooner, but you will also find examples where there is almost no difference.


What is a rhumb line? Can anyone explain what a rhumb line is and how it is different from the great circle route?

This what the internet says:

  Rhumb lines are tracks with a constant track direction between two points on a sphere and therefore must be a longer distance than a great circle track.

From pprune.org

What does it mean to have a constant track direction?

a rhumb line, rhumb, (/rʌm/) or loxodrome is an arc crossing all meridians of longitude at the same angle, that is, a path with constant bearing as measured relative to true or magnetic north

From: Wikipedia

If continued, all rhumb lines except the ones following a  track of 90 or 270 degrees end up in either the North or South Pole.

If continued, all great circle lines end up back where they started from.

As for the part of the question about constant track direction: track is defined by ICAO as

  The projection on the earth’s surface of the path of an aircraft, the direction of which path at any point is usually expressed in degrees from North (true, magnetic or grid).

So, to maintain a constant track would mean that North would always be in the exact same direction from you as you move on. This would eventually take you to one of the poles, unless of course, you were maintaining a track of 90 or 270 degrees.

The picture above shows a constant track of about 75 degrees.


What is the purpose of these winglets on the Chinese version of the An-2? The Shijiazhuang (now part of AVIC) Y-5B, a Chinese version of the Antonov An-2, has winglets of a particular type:

Photo by Linshuo at Airliners.net

Quite a futuristic design for this old biplane of 1958, still in production. Not all version of the Y-5 have such wingtips though:

B-50AG. Photo by Weimeng, AirTeamImages

What are the advantages of these winglets in this case, compared to more common ones? Why only one the upper wing? Are they used on other aircraft?

As you said, the Y-5 and Y-5B are Chinese variants of the Antonov AN-2. The Wikipedia page gives this info on the Y-5B:

  Shijiazhuang Y-5B-100 – Y-5B aircraft fitted with triple tipsails on the upper wing tips, which reputedly gave 20% higher climb rate and improved L/D ratio by 15%.

Here is a research paper on tipsails which may help a little bit.

There doesn't seem to be a lot of empirical evidence of the performance gains that China claims with the Y-5B. I can't find examples of the triple tipsail design used on any other aircraft.

Just look at the aircraft though, all the struts, wires, hinges, etc hanging out in the wind, and these 3 little tip sails improve L/D by 15% and climb rate by 20%? That's a hard pill to swallow. If it were that simple, it would be a feature of nearly every aircraft.


Why does an aircraft leave a white smoke trail? Why does an aircraft leave a white smoke trail?

Actually, there are three types of trails an aircraft can leave in the sky:

1. Condensation of water vapor in the exhaust gas and/or the wake

This needs the very cold, very dry air at higher altitudes between 6000m and 12000m. Water vapor in the exhaust stream condenses and, pushing the local air above its saturation water content, forms a white, frozen mist. Also, particles from partially burnt fuel form condensation cores wich stabilise the contrail and let it grow over time from humidity already present in the air. Depending on the atmospheric humidity, these contrails disappear rather quickly by sublimation or can stay in place for hours and even grow into cirrus clouds. They are called condensation trails or short "contrails".

Cirrus clouds triggered by aircraft contrails (picture source)

While the added water vapor in the exhaust gas helps in contrail production, the condensation happening in the pressure field around an aircraft can already produce a contrail all by itself. If the relative humidity is close to saturation and the condensed droplets freeze quickly, the aerodynamic contrail will disappear rather slowly. The same condensation happens also at lower altitude but will not leave a contrail  in temperatures above 0°C. Fog (liquid droplets) will vaporize quickly, but when frozen the condensation will last longer, until the water is re-absorbed by the air by sublimation, a much slower process than evaporation.

Engine and aerodynamic contrail forming behind an A340 (picture source)

2. Smoke from unburnt or partially burnt fuel

This was prevalent in early jets and allowed to spot them from a distance - just follow the black line, at its tip is an aircraft. Smokeless combustor cans which allow more fuel-air mixing put an end to this. For more information I recommend the excellent web page contrailscience

This B-47 uses rockets to accelerate quickly which leave the biggest smoke trail, but also the old J-47 left a lot of smoke behind (picture source).

3. Oil mist or smoke flares

The third source is shown in your picture: Oil is injected into the hot exhaust stream which forms a dense mist. This can be done with jets and piston engines, and gliders or parachutists use smoke flares. Once they are ignited (in most cases electrically) they burn down and cannot be switched off.

Smoke flares on the wingtips and fuselage of a glider (picture source)

There are many more things that can be sprayed from an aircraft (fuel, obviously, when it has to be dumped in an emergency, fertilizer or insecticides, silver iodide to seed clouds), but these are special cases. I encourage you to visit contrailscience.com for an exhaustive list of those other cases.

LS-10 glider dumping ballast water (picture source)


Why would a country prefer to purchase Su-35 rather than Su-30MK? Given that the Su-35 is merely an upgrade from the Su-27, why is Indonesia purchasing Su-35?

There can be many reasons for such a choice. The first is a single seat air-defense fighter, the other is a two-seat multirole  air-superiority fighter according to Wikipedia. The cost can be another reason; depending on configuration it seems that the two aircraft have an overlap with both types starting around USD \$40 million per aircraft.

Indonesia already operate a fleet of several single-seat types, such as the Su-27, F-5 and F-16, so it might simply be easier to transition to another single seat fighter. They do have a small number of Su-30 already, so it could also be a desire to use each type for the optimal mission, rather than having one type do everything.


Airplane Strobe Light Pattern? I saw this question on Google Plus and it seems to be a good question to put here.

  Is there a flash pattern for the strobe lights?
  I think I've read that Airbus has ~2 flashes/sec and Boeing has ~1 flash/sec. I've seen both patterns in the air but I didn't know the aircraft type.

It appears that the flash sequences in Airbus and Boeings are different. For example, the following image gives the flashing sequence in Airbus A320:

Image from LED Anticollision Lighting system for A320 by UTC Aerospace Systems

Note the differing flashing sequences of different lights. Also, see this question.

As far as regulations are concerned, 14 CFR 23.1401 - Anticollision light system states that:

  (c) Flashing characteristics. The arrangement of the system, that is, the number of light sources, beam width, speed of rotation, and other characteristics, must give an effective flash frequency of not less than 40, nor more than 100, cycles per minute. The effective flash frequency is the frequency at which the airplane's complete anticollision light system is observed from a distance, and applies to each sector of light including any overlaps that exist when the system consists of more than one light source. In overlaps, flash frequencies may exceed 100, but not 180, cycles per minute.


How is vibration isolation achieved in helicopters? In many helicopters, they say they have reduced the vibrations significantly, but how is this isolation being achieved?

There are many techniques.

Passive reduction techniques involve designing the powerplant, transmission, gearbox and particularly the rotor(s) to minimize vibration. Designers carefully arrange all the moving parts to be as closely balanced as possible. They can be mounted using flexible parts and springs to damp vibrations (the same principle behind the shock absorbers in an automobile). The sophistication of helicopter design has evolved over time as engineers learn more about the characteristics of helicopters and how mechanical parts behave. Computer-assisted design has also allowed for huge improvements here as moving parts can be simulated in great detail to optimize each individual part for minimum vibration.

Active systems work by using accelerometers to sense the vibration of the helicopter at certain points in real time. This data is then used to shake a reaction mass back and forth to create vibration opposite to that of the rest of the helicopter. The two opposite vibrations cancel each other out. Effectively, the active system is using electrical power to dump all of the vibration energy in the helicopter into a small mass, so the helicopter stays still while the reaction mass in the active system shakes to absorb the energy. Such systems are already in common use in large transport helicopters and are becoming more prevalent in smaller helicopters as well.


Do helicopters use more fuel when hovering? This answer says

  A helicopter uses a LOT more fuel hovering than it does in forward flight.

Is this correct? Why?

Yes it is correct that helicopters use more fuel when hovering: the engine needs to apply more power to overcome drag. Here is a graph of the engine power required for different airspeeds, from J. Gordon Leishman, Principles Of Helicopter Aerodynamics:

The line for total power goes down between 0 - 70 kts with increasing airspeed, this is caused by the line for induced power: power required to overcome the induced drag of the helicopter blade. The total required engine power is the summation of:

Induced power. The power required to overcome the induced drag of lift creation, further detailed below. Propulsive power relates to the engine exhaust velocity now being helpful, and to the rise in induced power at higher speeds due to compressibility drag.
Profile power, required for the blade profile drag.
Parasitic power, for the drag caused by the air frame, rotor hub etc. Zero in the hover, very dominant at top speed. Helicopters have shapes that are way less aerodynamic than fixed wing planes, and this source of drag becomes very significant at higher speeds.
Tail rotor power. Up to 20% of the main rotor power both in the hover and at top speed, very low in the middle due to the helpful vertical tail. At top speed the torque of the main rotor is high and the tail rotor must do more work, unless the vertical tail can be adjusted.

Induced power is dominant in the hover. Induced drag is caused by the backwards tilt of the lift vector: the higher the angle between blade and free stream, the more the vector is tilted backwards, which causes both loss of lift and increase of drag. The equation for lift L is:

$$ L = C_L \cdot \frac{1}{2} \cdot \rho \cdot V^2 \cdot S$$

and at a given altitude, the two variables here are $C_L$ (lift coefficient) and $V$ (airspeed at the blade). $C_L$ is an approximately linear function of angle of attack at the blade, so lift increases linearly with blade tilt-back and quadratically with increasing airspeed over the blade.

Above graph from Leishman shows the velocity distribution over the blades when hovering, and at airspeed. Quite a complicated situation - when hovering, the airspeed reaching the blade is only the rotational speed of the rotor, at forward speed the blade going forward has rotational speed plus airspeed.

The helicopter does not roll over and both forward blade and retreating blade deliver the same amount of lift, with the rearward going blade tilted back more than it was in the hover. But the forward going blade is tilted back a lot less: airspeed has a quadratic influence.

Note that the circle in the plot at fwd airspeed is not stalled flow, but reverse flow: the air streams in at the back of the blade. So drag is now negative, the airstream helps to propel the blade! However there is loss of lift in the reverse flow area.

Induced power reduces with airspeed at first according to the simple 1-D impulse consideration (more air mass through the disk), and later increases as the disk is increasingly tilted forward and must do more work to overcome losses from rotor profile drag, airframe parasitic drag, and compressibility drag.

There is also an interference effect of the downwash over the fuselage: in the hover the air streams straight down, while in forward flight the rotor wash is more aligned with the fuselage, catching more of a streamline shape. Parasitic drag is of course dominant at top speed, while offloading the rotor by using fixed wing surfaces reduces the induced power at high speeds - but from hover to moderate forward speeds it is purely the reduction in lift induced power that creates translational lift.


What are the requirements to get a private pilot's license in Indonesia? I am interested to get license to pilot small civil aircraft (up to max. 4 passengers including the pilot him/herself). I read here that there is no age limitation to get the license as long pass the medical check.

What is the required knowledge to get the license? Is anyone here has the shareable pilot training and testing material?

Edit:
I am and Indonesian and stay in Indonesia. The license I want to get is for private slow aircraft such as Cessna which the speed should not more than 300km/h. Passengers are family members or friends, not commercial.

The Indonesian air regulations include CASR 61 Licensing of Pilots & Flight Instructors, which has all the detailed requirements for getting a Student license (subpart C) and then a Private license (subpart D). To get a more 'friendly' overview of what they really mean, I would look for a local flight school that can explain the practical steps.

Interestingly, the Indonesian regulations appear to be very closely based on the US ones.


Can a commercial pilot with MPL , obtain PPL for general aviation in the UAE? Is it possible for an airline pilot in case he would like to fly GA aircraft like c152/172 obtain the PPL license without going through the whole process?

Note: You did not specify a country. I will answer for EASA.

You don't need to obtain a PPL, you may use the MPL (Multi-Crew Pilot Licence) if you fulfill the requirements. From EASA Part-FCL (emphasis mine):

  FCL.405.A MPL — Privileges

  (a) The privileges of the holder of an MPL are to act as co-pilot in an aeroplane required to be operated
  with a co-pilot.

  (b) The holder of an MPL may obtain the extra privileges of:

  (1) the holder of a PPL(A), provided that the requirements for the PPL(A) specified in Subpart C are met;

  (2) a CPL(A), provided that the requirements specified in FCL.325.A are met.

  (c) The holder of an MPL shall have the privileges of his/her IR(A) limited to aeroplanes required to be
  operated with a co-pilot. The privileges of the IR(A) may be extended to single-pilot operations in
  aeroplanes, provided that the licence holder has completed the training necessary to act as PIC in
  single-pilot operations exercised solely by reference to instruments and passed the skill test of the
  IR(A) as a single-pilot.

You can find the requirements of Subpart C in the same PDF on page 145f.


If a pilot ejects, what is the autopilot programmed to do? If a pilot uses their ejector seat during flight, what is the autopilot programmed to do?
As a developer myself, I'd want to build in a way for the plane to try and save itself if possible (to save money) by auto-landing, or at the very least, calculate the nearest least-populated area for a crash-landing. So I'm wondering if anything like this is even written into the software.

I would want to build in a way for the plane to try and save itself if possible (to save money) by auto-landing

Had the situation allowed saving the airplane the human pilot would definitely have tried that first. The fact that a trained fighter jet pilot decided to eject from an aircraft knowing that the ejection was a last resort and could be deadly, signifies that the plane was not able to be flown safely anymore.

On top of numerous irrecoverable problems at that point, one of the most significant issues is the fact that ejection destabilizes the flight path and the increased drag (because there is no longer a canopy on top) makes it even harder to safely glide that jet, let alone land it somewhere.

There is nothing much autopilot can do at that point.

There have been two famous incidents that are related to your question but afaik neither of them involve Auto Pilot.

1989 Belgian MiG-23 crash
Cornfield Bomber

It's just like saying I know the airplane can be saved but my computer will take care of it, I'm outta here. See you at the Court Martial.

Some commentators have noted that I did not answer one basic question:

  Don't forget to answer the question "If a pilot ejects, what is the autopilot programmed to do?", even if the question seems moot

This question is too broad: there are numerous models of fighter jets all around the world, built by a number of manufactures and internal details of which are closely guarded secrets. You are not going to generally find out a manual on the web listing all the actions that the autopilot software will perform after a bail out. If the OP can narrow down the question to a certain model one can research and try to find something but I don't believe its going to be an easy find. Hence I'm sorry I don't have an answer to that question. I hope someone more knowledgeable goes ahead and posts an answer to that.


Why can't there be more than 4 anti-shock bodies on each wing? Most airliners have 3 or 4 shock bodies to reduce wave drag. But why can't there be more anti-shock bodies per wing?

There is no reason to limit the number of anti-shock bodies to 3 or 4. In most modern aircraft, the anti-shock bodies are the flap track fairings which usually house the flap mechanisms.

As such, their number is determined by among other things, the wingspan, the size of control surfaces and the number of actuators required for their actuation etc. This usually limits their number to around 4 due to weight and other considerations.

However, there is no reason there should only be 3 or 4 of them. For example, the Antonov An-225 Mriya has a whole lot of them.

Source:www.avioners.net


What is this squawk 7777 target at an altitude of 62,700' over Germany? Can anyone shed any light as to what this is (circled in white)?

This is a military test transponder, not a real aircraft. The callsign GAFTT08 stands for German Air Force Test Transponder 08. When you zoom in on the map, you can see the reconstructed position move in a pattern around the fixed true position:

(adsbexchange.com)

As far as I can tell, the military does not publicly say what exactly they are doing here. The only sources I could find are from forums:

  GAFTTxx = German Air Force Test Transponder

(flugzeugforum.de)

  German Air Force Test Transponder. So not an aircraft, not a drone. Don’t know why it is online all the time, but it is. Sometimes over Würzburg, sometimes over Ingolstadt.

(forum.scramble.nl)

Additionally, the squawk code of 7777 is used in Germany for fixed test transponders according to Wikipedia (thanks to ymb1 for pointing this out):

  7777 US, Germany, Belgium, Netherlands: Non-discrete code used by fixed test transponders (RABMs) to check correctness of radar stations (BITE)

(List of transponder codes - Wikipedia)

This is also confirmed by the following ICAO definition:

  Code 7700 is reserved for recognizing an aircraft
  in emergency. (Codes 7711 to 7717 and 7721 to 7727 are
  reserved for SAR operations and code 7777 for monitoring
  the ground transponder.)

(ICAO - SSR CODE ASSIGNMENT SYSTEM, emphasis mine)


How is the cruise speed of an aircraft chosen? Does cruising speed of aircraft depend upon mass of aircraft?

I am asking this because as lift is generated to overcome the gravitational forces ($mg$). And lift is proportional to square of the aircraft velocity.

The speed of the aircraft in cruise is determined by the forces in the horizontal axis: thrust and drag. Weight and lift are forces in the vertical axis; they do pop up in the horizontal axis, but are relatively tiny in cruise.

Image source

At low airspeeds, induced drag is the dominant factor: this is the drag that is proportional to lift and weight. At cruise speeds, induced drag drops off and parasite drag rises quadratically with airspeed. It is drag associated with the aerodynamic shape of the aircraft. At any weight, the most beneficial shape is the one that aligns the fuselage best with the free air stream: tilt the nose up or down from the Angle of Attack for minimum parasite drag and drag will increase, at any speed and weight. Wind tunnel tests and Computed Fluid Dynamics are the tools used for establishing minimal form drag.

However, for straight and level flight the vertical component of lift must indeed match the weight, so one of the parameters of the flight state must be tuned in order to get zero climb rate. Changing cruise speed is indeed one of the degrees of freedom to change lift, but not the best one. In the aircraft aerodynamic axes, lift L is given as $$L = C_L \cdot \frac{1}{2} \cdot \rho \cdot V^2 \cdot S$$

S is wing area, usually a constant that cannot be changed during cruise. So the degrees of freedom to change lift are:

Change lift coefficient $C_L$: this is done by changing Angle of Attack, by pitching up or down. Doing so creates extra drag and fuel burn, the least amount of drag is generally with the fuselage aligned with the free stream.
Change air density $\rho$: fly higher or lower. This is what is done when the aircraft gets lighter due to fuel burned: at higher altitude there is less air resistance and less thrust needs to be delivered by the engine, improving fuel burn without slowing down.
Change V. Flying slower as fuel is burned is beneficial for fuel burn per hour - but it takes longer for the aircraft to arrive, so fuel is burned for more hours.

So for varying weight, it is best to vary lift by varying altitude. Long range cruise aircraft would have the least fuel burn if they could gradually climb as fuel weight diminishes, however there are air traffic corridors which the aircraft needs to stay in. Cruise climb is done in steps instead.

From this lecture, which also provides equations for cruising at constant altitude (varying velocity) and at constant velocity (varying altitude). The latter wins.


What is CBIR & Basic IR? I know that the IR - Instrument rating - is the full-blown option to be allowed to fly IFR. I also know that EIR - En-route Instrument rating - is an option to have a license that's restricted to fly IFR except for during takeoff and landing.

What is CBIR and what is Basic IR? I also heard that Basic IR will "come soon" and "replace EIR". What's the roadmap for EASA instrument ratings in the next years?

The Competency Based Instrument Rating (CBIR) allows you to gain an IR in less hours than the "full" course, by either crediting previous experience or licenses.

I held a UK issued IR(R) (old IMC rating), which meant that I had approx 60 hours IFR time when starting my IR. A full IR would have meant 45 hours training, whereas the CBIR allowed me to do just 15 hours (in accordance with EASA Part FCL, Appendix 6).

The BIR, as far as I am aware, is effectively going to mirror the UK IR(R) but make it a full EASA rating. That isn't confirmed however, as I haven't yet seen any official documentation from EASA.


What prevents the use of a multi-segment ILS for non-straight approaches? An ILS, consisting of a localiser beam to provide lateral guidance (which can also be used on its own for a non-precision approach) and a glideslope beam to provide vertical guidance, is (currently) indispensable for precision approaches in IMC, but comes with a few disadvantages.

Chief among those is the fact that an ILS only supports approaches that are ramrod-straight all the way in from the outer marker, when such an approach path is often impossible or undesirable...

...sometimes because something too solid to fly through is in the way (for instance, the infamous approach to runway 13 at Kai Tak, which, due to an inconveniently-placed mountain, necessitated coming in at a large angle to the runway and then making a sharp right turn at very low altitude at almost literally the last moment; an instrument guidance system - basically an ILS without the “landing” part - was added in the 1970s to provide precision guidance for the part of the approach before the turn, but the turn itself and the final approach segment still had to be hand-flown visually, an exceptionally difficult task even in good weather)...
...and sometimes because someone else is using part of the airspace in question (for instance, the four major airports in the New York area [JFK, la Guardia, Newark, and Teterboro] have numerous intersecting approach paths, which, as the approaches can’t be bent or segmented to keep out of each others’ way, frequently forces la Guardia and Teterboro to land aircraft on runways with strong crosswinds [because the ILS approach paths for their more optimal runways would risk causing MACs with aircraft on ILS approaches into JFK and/or Newark]; on the other side of the continent, the approach paths coming into LAX from the east pass near or over Ontario, which has caused quite a number of near misses in the vicinity of the latter airport).

It doesn’t seem, conceptually, like it should be too hard to break up an ILS approach into two or more segments, each with its own localiser and glideslope, and with the beams from the pre- and post-bend segments intersecting at the bend in the approach path.  As most aircraft are unable to turn on a dime, they would need to start turning a bit before the bend in the approach, but this could be easily handled by having another instrumental aid (for instance, a third localiser) indicate when to start turning; if the bend in the approach were sharp enough for the aircraft to have trouble locking onto the post-bend beams, another localiser and glideslope, with their beams tangent to the midpoint of the turn, could be used to assist the aircraft round the bend.

All of this would also work for segmented localiser approaches, with the added advantage of being easier to implement (no need for the multiple glideslope antennae, just the localiser ones).

Here be an illustration of what I’ve got in mind:

Why aren’t segmented ILS and localiser approaches used in practice?

See here, pages 5-23, 5-24.  Things have advanced well beyond ILS for that kind of approach.

https://whispertrack.com/pdf/faa_handbook.pdf

  REQUIRED NAVIGATION PERFORMANCE
  The operational advantages of RNP include accuracy
  and integrity monitoring, which provide more precision and lower minimums than conventional RNAV.
  RNP DAs can be as low as 250 feet with visibilities as
  low as 3/4 SM. Besides lower minimums, the benefits
  of RNP include improved obstacle clearance limits, as
  well as reduced pilot workload. When RNP-capable
  aircraft fly an accurate, repeatable path, ATC can be
  confident that these aircraft will be at a specific position, thus maximizing safety and increasing capacity

  To attain the benefits of RNP approach procedures, a
  key component is curved flight tracks. Constant radius
  turns around a fix are called “radius-to-fix legs,” or RF
  legs. These turns, which are encoded into the navigation database, allow the aircraft to avoid critical areas
  of terrain or conflicting airspace while preserving positional accuracy by maintaining precise, positive course
  guidance along the curved track. The introduction of
  RF legs into the design of terminal RNAV procedures
  results in improved use of airspace and allows procedures to be developed to and from runways that are otherwise limited to traditional linear flight paths or, in
  some cases, not served by an IFR procedure at all.
  Navigation systems with RF capability are a prerequisite to flying a procedure that includes an RF leg. Refer
  to the notes box of the pilot briefing portion of the
  approach chart in figure 5-17.

The Approach in Fig 5-17 has 5 turns left & right!


Is a one foot landing possible? This video shows an aircraft touching down like a helicopter on some gravel, is this possible or is the video a fake? Are there any other videos out there?

Facebook video
Similar one on YouTube

It's a STOL (short takeoff and landing) plane, landing in strong headwind. It's perfectly possible.

You can find more examples on YouTube.


Do airlines staff extra crew members when disabled persons are check in? The question "How are disabled passengers evacuated during emergency?" made me wander if minimum crew number required by regulation are enough in case of passengers requiring extra care in case of evacuation.

My question is restricted to cases where airliners know in advance that a passenger with reduced mobility, unable to run or jump (let's say the passenger requires either a wheel chair or crutch to walk) is scheduled on a specific leg. Do airlines staff extra cabin crew member(s) to improve handling of everyone in case of emergency evacuation?

In almost two decades of flying for airlines, I've never seen it done, and never heard of any program to facilitate such staffing.


Could a landing gear jettison mechanism be practical when ditching? Reading this answer about GA aircraft ditching, I wondered if, considering conventional fixed landing gear aircraft (taildraggers) which often operate overwater, having the ability to jettison the landing gear before ditching would increase safety by reducing chances of flipping inverted when wheels contact water?

Regardless of how this mechanism would work, explosive bolts or manual release mechanism, would this added complexity/weight be practical considering ditching probabilities, and are there been studies about this?

Here's a video showing one Cessna with retractable landing gear, ditching gear up, avoiding it to flip inverted.

https://www.youtube.com/embed/8rr2ZjGbdAA?start=23&end=33

According to at least one source (based on NTSB data) there were 179 registered ditchings of GA aircraft over a period of 8 years, or an average of approx 22 per year. The trend however were going downwards from 30 in the mid-80s to 12-15 ditchings in the mid-90s when the study ended.

In all 22 fatalities were registered, with an 88% overall survival rate but a 92% egress rate. The egress rate is what is important for your question. Discard the long-range ocean-ferry flights and this number rises to 95%.

It's worth mentioning that there numbers are for registered ditchings. Unregistered ditchings are more likely to be successful than not, so the real survival rate is likely to be higher.

According to the report:

  "Where and when you ditch matters more than what you ditch. Examining the fatal accidents, we found that two-thirds of the 22 occurred during the winter in cold or temperate climates and 12 percent are what we call "blue water" ditchings in the open Atlantic or Pacific, done by ferry pilots on extraordinary missions in light singles or twins, or fish spotters operating far from shore."

If you want to have a landing gear that can be jettisoned, chances are that it would add quite a bit of complexity and maintenance to address a non-problem. 9 of the 22 fatalities involved an aircraft with retractable landing gear, but the study makes it clear that the status of the landing gear was unknown, so we don't know if or how this affected the statistics.

The problem isn't ditching with or without a landing gear, it's the fact that you're ditching in the first place. And when it happens it most likely does so without you having appropriate survival gear.


How dissimilar are redundant flight control computers? Facts

On Airbus aircraft there are computers to secure the flight envelope, or to move the control surfaces. FADECs totally control the engines. Computers take decisions in place of the pilots, or even against their commands. Boeing aircraft have similar computers, even if the crew has more authority.

A330 electronic bay, source, photo by 'swiss_a320'

Safety implications

Being critical, systems are redundant and supervise each other to detect possible failures and isolate failed components. However a computer can still be developed from faulty specifications, or be wrongly manufactured, and a program can contains bugs. If the same defect is present on all computers on the production line, the purpose of redundancy may be defeated, as they wouldn't be able to detect erroneous behavior.

This is better stated in this article:

  Because of the severe consequences resulting from a single point of
  failure, hardware redundancy is critical in DAL A systems. But if the
  aircraft uses a redundant architecture built with similar channels,
  that system will still be susceptible to common mode failures that can
  cause all channels to fail in the same way.

Question

What are the principles used in aviation to reduce the possibility for redundant computers to fail or to make the same errors at the same time?

As far as Airbus is concerned:

Each unit is composed of two dissimilar boards, one driving the output and the other checking it. Dissimilar means both different CPUs and chipsets (A320 uses i386 (Intel) and m68k (Motorola); newer models use different combinations, basically whatever was widely used at the time they were designed) and software written by two independent teams.
There are fail-overs, two or three depending on the system (IIRC the unit reading the side-sticks is the only one with four copies).
The two main axes, pitch and roll, are controlled by two different systems. ELAC controls elevator and ailerons, SEC controls horizontal stabilizer and spoilers. This is two completely independent chains including different actual control surfaces except for the side-sticks.
A320 has (hydro)mechanical backup for pitch via the trim wheel and yaw via the pedals, utilizing yaw-roll coupling for roll. This works even with complete electrical failure. IIRC the backups on newer models don't though (because complete electrical failure has never happened).


For jets, how can we show that 1/2*ρ*V^2 is equivalent to 1481.3*δ*M^2? In Roskam's book, we find the following relationship given for climb performance in jet aircraft:

  Thrust requested = $D$ = $C_d \cdot (1/2 \cdot \rho \cdot V^2) \cdot S = C_d \cdot (1481.3 \cdot \delta \cdot M^2) \cdot S$

How can we show that $(1/2 \cdot \rho \cdot V^2)$ is equivalent to $(1481.3 \cdot \delta \cdot M^2)$?

SOURCE:
Author: Jan Roskam
Title:  Airplane Aerodynamics and Performance
Paragraph "9.2 CLIMB AND DRIFT-DOWN PERFORMANCE OF JET AIRPLANES"

Using the Mach number definition $M=\frac{V}{\sqrt{\gamma RT}}$, the ideal gas equation $p=\rho RT$ and the atmospheric pressure ratio $\delta=\frac{p}{p_0}$:

$$ \frac{1}{2} \rho V^2 = \frac{1}{2} \rho \cdot \gamma RT \frac{V^2}{\gamma RT} = \frac{1}{2} \gamma p \cdot M^2 = \frac{\gamma \cdot p_0}{2} \cdot \delta \cdot  M^2 $$

With $p_0=2116.2 \text{lbs}/\text{ft}^2$ and $\gamma = 1.4$ you get the desired result.


How much difference in heading/bearing between consecutive legs is "officially" considered a turn? While examining FAA's TERPS manual (Order 8260.3D) and PBN manual (Order 8260.58A), I noticed two seemingly contradictory statements.

  TERPS 8260.3D Chapter 14. Departure Routes, 14-3-4 . Construct turning segments when the course change is more than 15 degrees

(emphasis mine)

Whereas in PBN manual, it seems that a deviation of 10 degrees is considered a turn.

  PBN 8260.58A 1-2-5,b,(1)a . [...] Not applicable for FB turns of 10 degrees or less.

(emphasis mine)

Am I missing something. Is there any consistent rule that states when a transition between legs of an Instrument Procedure is considered a turn or a straight flight?

I will have to answer my own question, since I have noticed that in FAA's PBN Manual it states:

  PBN 8260.58A 1-2-5c . Turn parameters. For OEA construction, a turn is indicated when the course change exceeds the alignment tolerance of 0.03 degrees.

So, at least as far as route design is concerned, the alignment threshold for turn indication is 0.03 degrees.


What fighters have both 1 & 2 engine versions? Northrop originally built the F-5 "Freedom Fighter" (and T-38 "Talon") with two engines. Later it was re-fitted with a single F404 engine from the F/A-18, re-designating it the F-20 "Tigershark" to avoid confusion. The first F-5A and T-38 flights took place in 1959.

[Addendum: There is no real contradiction, the T-38 "Talon" was a two place trainer version of the F-5 "Freedom Fighter". Most aircraft don't re-designate between one and two seat versions, but Northrop or the military did in this case.] See the history of the F-5 YouTube Video

"Though the USAF had no acknowledged need for a light fighter, it did procure roughly 1,200 Northrop T-38 Talon trainer aircraft, which were directly based on the F-5A." https://en.wikipedia.org/wiki/Northrop_F-5

"The F-5G was an advanced single-engined variant later renamed the F-20 Tigershark." https://en.wikipedia.org/wiki/Northrop_T-38_Talon

Have any other fighters (world wide) offered a fighter with one and two engine models?

Twin engine F-5 "Freedom Fighter".

Single engine F-20 (F-5G) "Tigershark". Wikipedia

The Republic F-84F Thunderstreak was a fairly normal early jet fighter, powered by a single Wright J65 turbojet engine.

Its mutant offspring, the Republic XF-84H "Thunderscreech" was a experimental turboprop fighter, powered by an experimental Allison T40 engine, which consisted of two Allison T38 engines, joined through a common gearbox.

This was a twin-engine aircraft from the maintenance point of view, since there were two sets of turbo-machinery to go wrong. It looked like a single-engine aircraft, and flew like nothing on earth, owing to the strange effects of two sets of supersonic shockwaves from the contra-rotating propellers hitting the wings several times per second. Its first test pilot refused to have anything more to do with it after the first flight; the second test pilot flew it eleven times, but Republic did not submit the aircraft for USAF trials.

Edit: The reason for doing this was that early jet engines were very fuel-thirsty, while turboprops got much better mileage. The propeller was supersonic because that was necessary to absorb the power in a small enough propeller to fit within the aircraft's ground clearance. It wasn't remotely a good idea, but it may have shown the USAF that jet-age aircraft development was harder than it had been in the piston-engine era.


Why does only one hydraulic intake line from the reservoir have a filter on the Arrow II? This is a portion of an Arrow II landing gear hydraulic system diagram.

I noticed that there are two intake check valves, one located on each side of the pump, that would allow flow from the reservoir.  Only one side indicates the existence of a filter.

Why do both sides not have a filter if they are both from the reservoir?

Why is it designed like that?

This design combines two advantages:

The system works reliably with one filter instead of two, saving a bit of cost, weight, and complexity
In case of a blocked filter, the gears can still be lowered (thanks @GgD for the hint!).

How it works

Gear down:

  When the flight deck gear selection handle is put in the gear-down
  position, a switch is made that turns on the electric motor in the
  power pack. The motor turns in the direction to rotate the hydraulic
  gear pump so that it pumps fluid to the gear-down side of the
  actuating cylinders. Pump pressure moves the spring-loaded shuttle
  valve to the left to allow fluid to reach all three actuators.
  Restrictors are used in the nose wheel actuator inlet and outlet ports
  to slow down the motion of this lighter gear. While hydraulic fluid is
  pumped to extend the gear, fluid from the upside of the actuators
  returns to the reservoir through the gear-up check valve. When the
  gear reach the down and locked position, pressure builds in the
  gear-down line from the pump and the low-pressure control valve
  unseats to return the fluid to the reservoir. Electric limit switches
  turn off the pump when all three gears are down and locked.

Gear up:

  To raise the gear, the flight deck gear handle is moved to the gear-up
  position. This sends current to the electric motor, which drives the
  hydraulic gear pump in the opposite direction causing fluid to be
  pumped to the gear-up side of the actuators. In this direction, pump
  inlet fluid flows through the filter. Fluid from the pump flows
  thought the gear-up check valve to the gear-up sides of the actuating
  cylinders. As the cylinders begin to move, the pistons release the
  mechanical down locks that hold the gear rigid for ground operations.
  Fluid from the gear-down side of the actuators returns to the
  reservoir through the shuttle valve. When the three gears are fully
  retracted, pressure builds in the system, and a pressure switch is
  opened that cuts power to the electric pump motor. The gear are held
  in the retracted position with hydraulic pressure. If pressure
  declines, the pressure switch closes to run the pump and raise the
  pressure until the pressure switch opens again.

Source: FAA

Aircraft Handbooks & Manuals: FAA-H-8083-31A, Aviation Maintenance Technician Handbook-Airframe Volume 2

chapter 13: Aircraft Landing Gear Systems, pages 13-18 to 13-20

Hydraulic fluid reservoir

Ideally, a hydraulic system could be a closed circuit without a reservoir. The actuators have two cavities, one to push the piston out, and one two pull the piston in. The total volume is constant, except for the volume of the piston rods.

A practical hydraulic system has to cope with the fluid displacement of the piston rods, leakage, geometric imperfections, and the thermal expansion of both, the equipment and the hydraulic fluid. A reservoir of hydraulic fluid is needed to allow fluid to enter or leave the system. This compensation flow could be very minimal. The fluid also needs to get filtered, because of possible impurities in new oil as well as possible contamination from the hydraulic equipment and conducts.

Shuttle valve

The shuttle valve is switching the routing of hydraulic fluid:

When the gears are pulled up, the return flow from the actuators goes to the reservoir, and fluid from the reservoir goes through the filter and the right valve to the pump.
When the gears are pushed down, the system is mostly a closed circuit. There might be some influx of fluid from the right valve, but that would be a small amount (unless the system is leaking badly).

Without the shuttle valve, there would be no point in the circuit where the main stream of fluid goes only one way. In such a design, there would be no place to put a filter out the contamination from within the system.


Is there a local UAS code database? Has anyone created (or proposed) a database or clearinghouse of local and state codes, restrictions and prohibitions applicable to UAS?

So far no one has created an official database. By official I mean one that you can count on to be correct and up-to-date. There are a few people who have created databases, but they all come with the caveat that they don't guarantee the info is correct and current.

The thing is, I don't really know if you could create a reliable database with the laws the way they are. A few states have stepped in and written a preemption against local ordinances, so in those it would be fairly easy to do. But in other states there'd be no way to keep up with ordinances enacted by the the thousands of county and local governments, many of which don't maintain an easily-accessible method of publishing their laws, and most of which are written by people who know little about uas, so the laws are often very vague.

The laws are also changing quickly right now, creating an untenable situation for drone operators. The US Senate is currently considering a bill that specifically legislates against any possible fix to this situation. It's really a complete mess.

A few of the databases I have found are:

Jonathan Rupprecht Law Office database
National Conference of State Legislators
Drone Law Today State drone law reference book


Aerodynamics of double winglets I've read here on Aviation SE that the aerodynamics of winglets on an aircraft are easily described as "extending the airfoil".  Thus, as I understand it, a winglet is like stretching the airfoil a few feet and "bending" it upward.

Now, this answer mentions the various types of winglets used in contemporary aircraft, but I'm not sure the B737-800s I've seen (such as the one in the below image) with double winglets perfectly matches any of those categories1.

source

Thus, my question is:  How can one best describe the aerodynamics (and benefits) of the second, downward-pointing winglet in the context of airfoil extension?

1 I claim that the 737-MAX's "split scimitar" as mentioned in fooot's answer is different than the aftermarket double winglet seen in the United (Continental) B737-824 in the image.

Winglets don't have some mysterious magical wing tip extending property.  They don't add to the total lift of the wing (except to the extent they are canted).

The best way to conceptualize them is they extract energy from the tip flow and convert it to THRUST which can be deducted from the induced drag.  They are little wings making lift (wing..let, see?), except the lift isn't up (unless they are canted, where there is a small vertical lift component).  They work the way boat sails propel a boat forward and were originally called "tip sails".

The flow striking the winget on top is curling inboard toward the fuselage so that there is an outboard angle of attack at the winglet's leading edge that creates a lift vector (being 90 degrees to the local AOA) inboard and slightly forward.

The split scimitar doohicky just flips the effect over to take advantage of unexploited flow below and behind. The flow striking the winglet on the bottom is angling outboard, causing a lift vector to be applied outboard and slightly forward (again at 90 deg to the local AOA).

If you examine most winglets you will see that they aren't just fins that "block" the flow. They have an airfoil cross section because, as I said, they are wings making lift... just not up.

The benefit of the lift being created at the winglet is only sufficient to exceed the thrust and weight penalty of the winglet itself at lower indicated airspeeds where the vortices are stronger.  For this reason you (almost) only see them on high altitude aircraft that cruise at low indicated airspeeds.


Why does IRS alignment take so much time? Home GPS systems (like your car navigator) is able to locate you in like a few seconds, but 737NG needs to align itself for 6-8 minutes.

Why do navigation systems in aircrafts take so long to align themselves?

Full name:
INS = Inertial Navigation System

IRS = Inertial Reference System

GPS faster? Yes and no
GPS is faster depends on which case we want to consider: Cold start, restart or operational use.

Cold start, like for example the first time we use the instrument: Inertial reference systems (IRS) are faster than GPS to deliver the first fix (TTFF): Less than 10 minutes (alignment) against 12.5 minutes for the GPS, the time to receive the constellation almanac from any satellite, a message which is valid for 90 days.

Warm start, like from one day to the next: GPS is faster, on the previous use, it stored the almanac. It now has to get the ephemeris for each satellite in sight, a 12s data transmission repeated every 30s (interleaved with almanac data) and valid for 2 hours. If the restart occurs within 2 hours and ephemerides for satellites in sight where cached, then it takes only a few seconds for the receiver to lock on the satellites data steam and to assess the ionospheric effects on radio signal velocity. IRS initialization takes the same time than for a cold start.

Operational use: IRS is faster, it can deliver a position immediately and continuously when properly aligned, while the GPS may be able to deliver only 10 or 100 updates per second. This parameter is important for fast aircraft, in 0.1s an airliner at M.82 cruises by more than 200m (if you were to use the car navigation system you mentioned in the question, with an update rate of 1s, there would be 2 km between consecutive fixes).

So for day to day operations, IRS is definitely slower to initialize as you observed.
GPS and IRS are not used the same way
We may wonder why these slow IRS are still seen in the plane electronics bay. First, they have two considerable technical advantages:

They are faster to deliver information when aligned. This capability is of prime importance for performance-based operations.

They don't rely on the availability of an external infrastructure to be operational (satellites, monitoring/control stations, SBAS overlays like WAAS, EGNOS, SDCM...) nor on radio transmission. Prior to 2000, the GPS was subject to selective availability under the decision of US generals and it still could suffer from intentional jamming.

But regardless of these advantages, IRS have not the same objectives than GPS. GPS is used to get a position, a Doppler groundspeed and a time reference. Other information, like heading, attitude, linear and angular accelerations, wind vector (with the help of the air data unit), drift angle, all critical data for a large automated aircraft, must be obtained through other sources, the first one being the IRS.
For example the quick determination of attitude parameter is critical for flight envelope protection and yaw damper control. This can only be done with an IRS. When an Airbus aircraft loses its 3 IRS, it loses most of the fly-by-wire protection and the rudder control falls back to mechanical linkage, so the pilot can control yaw with pedals, feel the aerodynamic efforts on rudder and maintain them within acceptable limits, now that yaw rate detection has been lost.
IRS actually provides primary data to various devices like auto-braking (anti-skid), vertical speed indicator or thrust management computer.
This explains why IRS are not going to be removed from electronics bay (it can be INS, IRS, IMU or today combined with air data units like ADIRU). On the other hand as they are subject to continuous drift, their position can be periodically updated by the GPS position (or most likely by a weighted mix of different sources).
Let me detail the principle behind IRS and GPS, and how they are started.
Time to get a fix from an IRS
An IRS is composed of 3 accelerometer-gyrometers pairs mutually perpendicular. Gyrometers quantify angular motions, like yaw or roll, and set a frame of reference for the accelerometers. The accelerometers quantity linear motions to update the aircraft position.

Overall principle of a strapdown IRS, source
During alignment the accelerometers sense the sum of gravity acceleration and centripetal acceleration (due to tangential velocity from earth rotation, proportional to latitude) in order to determine the horizontal plane (from the gravity field), true north (from earth rotation axis) and latitude (from centripetal acceleration). But there is a challenge:

Determining pole axis requires knowing the local centripetal acceleration, which in turn depends on latitude, and

determining which part of the locally sensed acceleration is due to latitude (and not to gravity) requires knowing the direction of earth rotation axis (true north). This is numerically solved using successive approximations of both data.

This process is convergent, and both latitude and north direction accuracy increases as the process is extended in time.

The convergence is slow and reaching an operational accuracy indeed requires the long time we know.

The slowness comes from earth rotation produces only tiny effects on the acceleration sensors, and we haven't found more practical sensors yet. The effects depends on the distance from earth rotation axis, larger at the equator than at the poles, hence alignment is also faster at the equator.
Accuracy of true north bearing increases with alignment time:

Source: An Improved Alignment Method for the Strapdown Inertial Navigation System
Alignment requires the unit to be motionless, any erratic motion decreases IRS signal/noise ratio which slows this process (passengers boarding, wind acting on the tail surfaces, etc).
GNSS principle: Need to know the current position of the satellites
To compute a fix, the receiver must know:

The satellites positions.
The time it takes for the signal from each satellite to reach the receiver.

... both data with an astronomical precision.
To compute the position, the receiver needs the orbital elements computed on the ground, from control and tracking stations measurements, uploaded to the satellites which act only as relays to broadcast this information along with a time reference from a very accurate embedded clock.
The GNSS receiver then computes the satellite current position along its orbit, and determines the time which has been required for the GPS signal to travel in atmosphere, providing the receiver distance to a known point in space. With 4 satellites and 3D triangulation techniques, the receiver position can be determined.
Satellites parameters are broadcast at different rates:

Rough parameters for all satellites, aka almanacs, valid for 90 days, are transmitted by all satellites every 12.5 minutes (so it may take up to 12.5 minutes to a brand new receiver to deliver the first fix).

Complementary precise parameters for a given satellite, aka ephemeris (which include specific corrections), valid for only two hours are transmitted by this satellite only, every 30 seconds, so it may take up to 30s for a receiver with a valid almanac to provide an accurate fix after restart (if the cached ephemerides for the currently visible satellites are too old), even if a rough fix can be delivered nearly instantaneously.


what Jobs can I get without atpl? I wonder what jobs I can get if I have ppl and cpl but no atpl?
is it possible to earn money from holding these licences?

Yes.  See FAR 119.1.  They have a list of other commercial operation you can do with a CPL but not an ATPL.


What is the difference between a flow and a checklist? Use of checklists is a 'special emphasis area' during FAA private and commercial checkrides but there are a lot of comments in pilot forums about using flows instead, often - but not always - in the context of airline operations.

What is a flow, and what is the difference between a flow and a checklist? When should a pilot prefer one or the other? Or are they used together?

Generally speaking a checklist is an actual list of items to check, and a flow is a pattern of movement across the aircraft controls (switches, dials, etc.) which will accomplish some subset of the items on a checklist.

A flow should be essentially "muscle memory" for a pilot and performed by rote, where a checklist may be more detailed and include more specific guidance.

As you can probably tell flows and checklists are closely related (with flows usually being derived from checklists). The two are complimentary tools that are used together: A pilot will follow a flow, and then verify that the required items have been completed using the checklist.
In larger/more complicated aircraft it's not possible to fully memorize some of the checklists, so flows are used to accomplish the "red box" immediate action items before proceeding to the full checklist.

As a simple example, consider the engine power loss flow & checklist for a Piper Cherokee.

Engine Power Loss Flow (Red Arrow & Numbers)

Mixture (Set appropriately - usually "Rich")
Throttle (Set appropriately)
Carb Heat / Alternate Air (On)
Magnetos (Both)
Electric Fuel Pump (On)
Primer (In & Locked)
Fuel Selector (On a tank that has fuel)

Manufacturer's Engine Power Loss Checklist (Blue Numbers)

Fuel Selector - Switch to a tank containing fuel.
Electric Fuel Pump - On
Mixture - Rich
Carb Heat - On
Engine Gauges - Check for an indication of the cause of power loss
Primer - Check Locked.
If no fuel pressure is indicated  check tank selector position to be sure it is on a tank containing fuel.
Ignition Switch - "Left" then "Right" then back to "BOTH."
Throttle and Mixture - Different settings.
(This may restore power if problem is too rich or too lean a mixture, or a partial fuel system restriction.)
Try another fuel tank.
(Water in the fuel could take some time to be used up, and allowing the engine to windmill may restore power. If power loss is due to water, fuel pressure indications will be normal.)

In this example the flow accomplishes nearly all the checklist items, but it does so moving over the panel in one direction. As a practical matter the flow is accomplished by just moving your hand along the bottom of the panel: "Push the mixture. Push the throttle. Pull the carb heat. Twist the mag key. Flip all the switches UP (on). Pull the primer and make sure it doesn't move. Move the fuel selector lever to the other tank."
Completing the flow takes less than 10 seconds and can be done with one hand while your other hand is pitching for best glide speed.

The manufacturer's checklist for an engine power loss moves around the panel in a more haphazard way, but it also adds a few items (checking the engine gauges & fuel pressure indication), and provides more specific guidance on possible causes like fuel contamination (water in the fuel) & how to deal with them. These items could be important if the memory items from the flow don't restore engine power, assuming you have time (altitude) to spend troubleshooting them.


Why do flight attendants on the 787 lock the dimmable windows at different phases of the flight? I’ve heard of many passengers complaining about the FAs locking the dim setting at different phases of the flight. Seems to be something the passengers definitely don’t like. And the passengers cannot change it. What is the reason for locking the window brightnesses?

On long-haul flights, most passengers will want to sleep, often including when the aircraft is flying through daylight. It's especially common on East-West long-haul flights for lots of people to want to sleep when it's daylight outside the aircraft, since the aircraft will often be crossing many time zones (and, during the summer months, also often flying through regions where it's daylight all day or nearly all day.)

Even on aircraft without dimmable windows, the cabin crew will normally tell passengers to keep window shades closed after the first meal service when the cabin lights are turned out for that reason. On the 787, the crew will dim and lock all of the windows centrally instead of telling the individual passengers to do it and this also prevents a passenger from undimming it and waking everyone up. Unfortunately, that does happen from time to time on aircraft with normal window shades where the crew can't prevent it and it is really annoying when you're trying to sleep if you don't have an eyemask on.

Here are some common examples of the types of long-haul flights where many or most passengers will be trying to sleep during hours where the aircraft is flying through daylight:

Flights from East Asia to the U.S., even though they're typically at least nominally "overnight" flights, will actually spend much of the time flying through daylight. The actual darkness outside will only last a fraction of its usual time, since the aircraft is flying in the same direction as the Earth's rotation at a pretty significant fraction of Earth's rotational velocity.
Flights from Europe to North American typically occur entirely during daylight. While it's 'daytime' on these flights, these days are often (quite literally) long days for travelers, so many will want to try to nap during the middle of the flight.
Late flights from North America to Europe often leave North America within an hour or two of midnight and land in Europe around midday, even though it's only 6-8 hours later. The latter half of the flight takes place in daylight, but passengers will still be trying to sleep.
Summertime flights from North America to East Asia will typically experience midnight sun. Even though these flights often occur almost entirely during 'overnight' hours, their flight paths frequently take them well into the Arctic Circle — sometimes even near the North Pole — where it will be daylight outside, even though it may be near midnight local time. This typically occurs around the middle of the flight, when nearly everyone will be trying to sleep. As most readers of this site will know, the reason these flights fly so far North is because that's actually the shortest path, since Earth is a spheroid. For example, this map shows the shortest-distance path from New York's Kennedy Airport (JFK/KJFK) to Shanghai's Pudong Airport (PVG/ZSPD):

Shortest path from JFK to PVG, generated on gcmap.com


How frequent are unpublished holding patterns outside general aviation? Flight regulations say that ATC may put an aircraft in a holding pattern, which is not published in the charts but I couldn't find any such case in FlightAware.

I have been searching on the Internet but I think I found almost only some information about flying uncharted holding patterns in general aviation and that it is something the ATC would like to avoid.

I'd appreciate any information on how often (and when or where) these uncharted holding patterns are used outside general aviation.

Not very frequent at all.

The need to delay traffic toward an airport is quite common. Usually, it is simply a question of fitting someone in a sequence of arriving aircraft, but there can be more severe cases, such as a runway change or ongoing emergency. In any case, ATC has a number of tools to use, and unpublished holdings are usually one of the last tools to be selected.

What we usually prefer to do is make use of radar vectoring instead. This is much more flexible, easier to work with and requires less time on the frequency. A normal holding pattern takes 4 minutes to fly. If needing to delay a flight for just a few minutes, using a holding will only really work if it works to delay the flight 4, 8, 12 etc. minutes. If I need to delay someone 6 minutes to fit in an arrival gap, then I could put them in a holding for 4 minutes and then vector them around for 2 minutes, but if I am going to be giving delaying vectors anyway, skipping the holding is easier.

On a busy radio frequency, available time on the frequency is everything for a controller. Nonessential or long messages can really ruin your day when working a tight approach sequence into a busy airport. Let's look at the phraseology for instructing an aircraft to enter a non published holding that the crew were not expecting:

  SAS123 proceed direct to ANDIE, alpha november delta india echo, and hold. Inbound track 120, right turns 1 minute legs.

Depending on your rate of speech, such an instruction may take almost 10 seconds to issue (and you can't just speak faster, because then the pilots will ask you to repeat yourself because they missed something).

If ATC needs to delay flight for a long time (say, more than 10 minutes), then holdings can definitely be an option, but in that case published holdings are used as much as possible. Published holdings are designed to ensure terrain clearance down to a specified lower limit, and, importantly from an ATC perspective, have defined lateral separation minima to other traffic. We are not allowed to use radar separation to aircraft established in a holding, so separating traffic from someone holding in a non published holding would be quite a hassle - but for published holdings, holding areas are defined, to which we can use radar separation. Finally, the phraseology for entering a published holding is much shorter:

  SAS123 hold over ANDIE as published.

If ATC needs to delay a flight for a short time (say, less than 10 minutes), using radar vectors is usually much easier, both for the controller and the crew. It is much more flexible (I can vector people around, and start creating a sequence 50 miles from the airport, even though there is no room near the airport yet) and can be used to delay flights any number of minutes (not just multiples of 4). And the flight crew just needs to adjust their heading, no need to calculate holding tracks, compensating for current wind and so on.

Of course there are cases, for example emergencies, where pilots may request to hold somewhere that does not have a published hold, and ATC will of course permit them to do so. But looking at the workload establishing a non published holding gives us, using a published holding or some other tool (radar vectors) is usually the preferred option.


Is there a relationship between turbojet engine rpm (N1 & N2) and fuel consumption rate? Image Source

N1 and N2 are the rotational speeds of the engine sections expressed as a percentage of a nominal value.

It is similar to the revolutions per minute (RPM) of a piston engine, expressed in percentage instead of in the actual rate of rotation.

They are different because they are characteristic on two-spool engines (see the figure below). The first spool is the low pressure compressor (LP), that is N1 and the second spool is the high pressure compressor (HP), that is N2. The shafts of the engine are not connected and they operate separately.

Image Source

Yes, these need to be roughly proportional for the engine to work, and will move towards an equilibrium if they are not.

The compressor provides the air for the combustion, and injecting more fuel will only generate a little extra power, which however increases the turbine speed, increasing air intake, which will allow more fuel to be burned, again increasing available power and so on.

In practice, if the air/fuel mixture is way off, compressor surges can happen, so in modern systems the engine computer will limit fuel flow.


What is the difference between ICAO and non-ICAO flight address? In document 260B, "Minimum operational performance standards for 1090Mhz Extended Squitter", on page 47 of the pdf, in the DF18 format they have mentioned for a particular CF(code format), "non-ICAO flight address".

So I wanted to know what the difference was between ICAO and non-ICAO flight address?

The use of the non-ICAO flight address field is described in the very same document, on table 2-11, page 53 of the PDF:

  AA field holds another kind of address for the transmitting
  ADS-B Participant: a self-assigned "anonymous" address, a
  ground vehicle address, or a surface obstruction address.

Ground vehicles and surface or tethered obstructions want to participate in ADS-B, but they don't have ICAO aircraft addresses, so they have to have their own addresses. Since these addresses aren't centrally assigned, the CF field is used to keep them distinct: otherwise, you could have a vehicle address that conflicts with an ICAO aircraft address.

The different kinds of addresses are further described in section 2.2.5.1.1 (p 172 of the PDF).


Can a four-engine aircraft with limited fuel gain extra range by shutting down one of its engines? I was reading the book Vulcan 607 by Rowland White who examines the details of a British bomber's mission during the Falklands War in 1982. At some point, the author wrote about the fuel shortage experienced by the crew of the four-engine Vulcan bomber during their return to their base. The author wrote that the pilot "considered shutting down one of the four Rolls-Royce Conway engines to get a little more range out of the remaining fuel...".

I have not heard of this type of procedure before, so I am wondering if the decision to shut down one of the engines to maximize fuel efficiency makes sense.

Assuming the aircraft is always flying at its optimal Lift/Drag ratio (= optimal angle of attack = optimal speed for a given weight and altitude), then the question is:

Is it more efficient to generate a given amount of thrust T with 4 engines x T/4, or 3 engines x T/3?

I would think that in the general case, it is not the case. Specific Fuel Consumption tends to increase with thrust (at constant speed):

Note: the above diagram is for Turbofans (Source: Airplane Aerodynamics and Performance, Roskam). It would be interesting to have similar trends for other types of engines (turboprops, turbojets, piston engines), but I could not find any!

On the other hand, it is possible that, in this particular case, the engines were simply working too far off their design point, so increasing thrust was improving their SFC.

Also, there is a problem with cutting one engine: The pilot will need to counteract the thrust asymmetry with the rudder, and this will have a significant cost in drag. Of course, the pilot could just cut 2 engines instead of one! :-)


Can you become FAA/TC commercial pilot with metal implants in hand? I have a friend who wants to be a pilot and he has metal implant in his hand. It doesn’t affect his hand movement at all. I know that he will need to check it out with a Civil Aviation medical examiner first before it can certainly be okay. The problem is he is going to have to travel to Canada or USA to study aviation and do his medical. He just wants to know if in general metal implants are a no go in aviation before he travels to start his process of becoming a pilot.
( yes it’s not a question for me it’s really for a friend... I am already a pilot)

The simplest way to answer this is to have your friend call an AME in the city they intend on training and ask them if they feel they will pass the required medical for a CPL. AME's are pretty forthcoming about this kind of stuff and they will often give you an idea over the phone if they feel there is a real issue. AME's are also the ONLY people that can definitively answer this question for your friend as they are the only people that can issue medical certificates.
Generally if the desired applicant has no practically limiting factors (in this case full use of their hand) the worst I would foresee needing is a Statement of Demonstrated Ability (SODA) which basically means they can show that they can execute the required actions of a pilot.
Under the Musculoskeletal section of the AME guidelines it states:

(b) No other organic, functional, or structural disease, defect, or
limitation that the Federal Air Surgeon, based on the case history and
appropriate, qualified medical judgment relating to the condition
involved finds

(1) Makes the person unable to safely perform the
duties or exercise the  privileges of the airman certificate applied
for or held; or

(2) May reasonably be expected, for the maximum
duration of the airman medical certificate applied for or held, to
make the person unable to perform those duties or exercise those
privileges.

If your friend can perform the duties of a pilot he should be ok.


Why doesn't the A320 have a dorsal fin like the 737? The A320 doesn't have a dorsal fin, but the 737 does. If the 737 is more or less a similar aircraft, why doesn't the A320 have a similar dorsal fin?

By Bill Larkins [CC BY-SA 2.0], via Wikimedia Commons

Boeing learned the value of a dorsal strake the hard way: On their civilian version of the B-17, the Boeing 307 Stratoliner, the first Boeing aircraft with a pressurized cabin, the lack of a strake ahead of the fin caused the rudder to lock in the hard-over position when the pilot demonstrated the capability of the aircraft to fly with two dead engines on one side. The aircraft entered a spin and crashed, and that was on a demonstration flight for prospective customers.

Early Boeing 307 with the two right engines off and props feathered (picture source). Note the deflected rudder and the rectangular windows in a pressurized fuselage. It worked because the pressure difference was small.

Late Boeing 307 in flight (picture source). The vertical was enlarged and had the strake added; the same vertical was also used on later versions of the B-17.

With today's hydraulically operated controls the risk of an uncontrollable hard-over is reduced, but exactly this happened to several early Boeing 737s. From the 737-300 on the strake was added and the control system (PCU = power control unit) was exchanged for a  modified version.

Airbus never had those issues and did not see the need to add a strake since the existing vertical could do its job in all conditions. A strake is worthless at small sideslip angles and will only help when the vertical is close to stalling due to extreme sideslip. Adding a strake will increase the wetted surface area and add friction drag, so Airbus did not include one.


Why do some airports have a non standard traffic pattern altitude? Some airports have a non-standard traffic pattern altitude.  For example KGXY is 800 feet.  Why is this?

Airports underneath controlled airspace may need to keep their traffic clear of controlled airspace, which may start from a typical altitude such as 1000Ft.

As is also mentioned in this answer, in April 2013 the standard pattern height was changed from 800 ft to 1000ft, possibly accounting for a number of airports still having the old "standard".


How can I identify the aircraft’s phase of flight in this picture? It’s me again, can anyone explain how to know the aircraft’s phase from this picture? Is it cruising or descending if so why its flaps up?

It is much lower than cruise altitude, I would guess roughly 4000-6000 feet.  The flaps are up because it is neither taking off nor landing.  Generally flaps are deployed around 2000 feet or below.  Given the proximity to New York City it is probably flying an arrival or departure procedure.

If you really wanted to dig deeper you could determine relative position and from Manhattan in the background and compare against published procedures into and out of the city's airports.


How were the fuel tanks sealed on the XB-70 Valkyrie? The Valkyrie flew at Mach 3.1, close to the SR-71's operating speed in cruise. For the SR-71:

Fuselage panels were manufactured to fit only loosely with the aircraft on the ground. Proper alignment was achieved as the airframe heated up and expanded several inches. Because of this, and the lack of a fuel-sealing system that could handle the airframe's expansion at extreme temperatures, the aircraft leaked JP-7 fuel on the ground prior to takeoff. (Wikipedia; emphasis mine)

And if my memory serves me well, and if Discovery channel got it right, the SR-71 needed to meet with a tanker right away because of this leakage.
What was the Valkyrie's workaround/fix? The Valkyrie's Wikipedia article doesn't mention leakage prior to in-flight expansion.
I wanted to initially ask about the MiG-31's fuel tank seals, as the USSR developed heat-resistant rubber[1] (and also special fuel like the SR-71 – the T-6) for that purpose, but since the MiG-31 is a lot cooler, it wouldn't have been comparable, though this piece of information might be relevant.

1: Wings of Russia TV documentary

According to Valkyrie - North American XB-70A by Steve Pace, leakage problems existed.

...engineering changes, weld stresses, and areas where it was not considered important to test-pressurize, combined to create an accumulation of leakage problems.  Brazing repairs to the leaking areas proved ineffective.

To the point that

The rearmost fuselage tank on XB-70A No. 1 became increasingly difficult to seal and therefore was never used.

The mitigation was

A non-metallic material made by DuPont called Viton-B was eventually used to coat the porous areas.

(p. 69)
It goes on to discuss that it still didn't work that well.
Fuel tankage diagram from the book


After the most recent US instructions, are there any prohibitions against transporting spare lithium ion/metal batteries in the cabin? Per the recent directive from Transportation Security Administration (TSA), except for medical devices, electronic devices which are larger than a cell phone/smart phone cannot be carried in the cabin of the aircraft from some countries into the United States. Many airlines are implementing this instruction and are requesting that all passengers traveling to the United States pack all electronic devices larger than a smart phone in their checked-in baggage.

The ICAO, IATA & FAA have already prohibited carrying spare lithium ion and/or lithium metal batteries in the aircraft hold area.

Is the transportation of spare lithium ion and/or lithium metal batteries in the passenger cabin of the aircraft now prohibited? Is it considered a rule violation to carry spare batteries this way?

Where can the spare lithium ion and/or lithium metal batteries be stowed during the prohibition period and how can they be transported?

Short answer: Yes.
Slightly longer answer: IATA changed the regulations within the 58th Edition of the Dangerous Goods Guidelines, effective January 1st, 2017. For passenger aircraft, lithium batteries are only allowed if they are installed in equipment. Standalone lithium ion cells or batteries are no longer permitted on passenger aircraft.
If you want to air freight lithium batteries: Air transport of Lithium batteries is only allowed if they are charged to 30% or less of their nominal capacity. Also, the cell must comply with the United Nations (UN) Manual of Tests and Criteria, Part III, Sub‐Section 38.3 (see page 394ff in this document) and proper packaging and documentation must be ensured.
The rules in the US and elsewhere differ slightly. From this Energizer document on US air freight:

Batteries must be of a type proven to meet the requirements of each test in the UN Manual of Tests and Criteria.

Batteries must be packed in strong outer packaging and be packaged in a manner to prevent short circuits and separated so that electrically active terminals cannot come into contact with each other.

The gross weight of the shippable container shall not exceed 30 kg. 

For lithium‐ion cell, the equivalent lithium content is not more than 1.5 g; or lithium‐ion battery, the aggregate equivalent lithium content is not more than 8 g.

The shippable container must be capable of passing a 1.2 m. drop test in any orientation without spillage of the contents of the packaging, damage to the batteries inside or shifting of the contents that could lead to short circuit.

The shippable container must be marked to indicate lithium batteries are present and that special procedures should be followed if the package is damaged.


What classifies as an ultralight vehicle? I am looking into the possibly of getting my pilots license and I noticed that it says you don't need a license for "ultralight vehicles".

What are ultralight vehicles?

I am located in the USA, and I am particularly interested in details for the states Utah and Washington.

A typical ultralight looks like this, although there are plenty of different designs:

Source: wikimedia.org

Ultralights in the US are defined and regulated by 14 CFR 103. The definition in 103.1 is:

  For the purposes of this part, an ultralight vehicle is a vehicle
  that:

  (a) Is used or intended to be used for manned operation in the air by
  a single occupant;

  (b) Is used or intended to be used for recreation or sport purposes
  only;

  (c) Does not have any U.S. or foreign airworthiness certificate; and

  (d) If unpowered, weighs less than 155 pounds; or

  (e) If powered:

  (1) Weighs less than 254 pounds empty weight, excluding floats and
  safety devices which are intended for deployment in a potentially
  catastrophic situation;

  (2) Has a fuel capacity not exceeding 5 U.S. gallons;

  (3) Is not capable of more than 55 knots calibrated airspeed at full
  power in level flight; and

  (4) Has a power-off stall speed which does not exceed 24 knots
  calibrated airspeed.

And 103.7(b) says:

  (b) Notwithstanding any other section pertaining to airman
  certification, operators of ultralight vehicles are not required to
  meet any aeronautical knowledge, age, or experience requirements to
  operate those vehicles or to have airman or medical certificates.

But, just because you can fly an ultralight without any license or training doesn't mean it's a good idea! You should definitely look into local ultralight clubs to help get you started safely. For example, the EAA has a lot of members who fly (and sometimes build) ultralights and they have some useful information on getting started.