Is any device installed on airplane to measure wind speed relative to the ground, and its direction? A device or tool which can measure actual wind speed to the ground rather than to the airplane. Also a device which detect the wind direction to the plane. The device I meant is something like this pitot. But unfortunately this pitot is measures the airplane relative to the air around it, not the ground.

The "wind speed relative to the ground" would just be the (vector) difference between ground speed and true air speed:

 (image source)

Most aircraft do not measure ground speed and track directly with instruments installed on the aircraft. It can be measured with a Doppler radar (see Peter Smith's answer), which is only used on military aircraft (mostly helicopters) today.

Ground speed and track can be determined with external tools:

DME: The Distance Measuring Equipment can be used to measure distances to fixed radio beacons equipped with DME (usually VOR/DME or VORTAC). If you know the angle at which you are flying towards/away from/to this station, you can calculate ground speed from the change in distance. Some DME instruments display this:

(image source)

When tracking a VOR, you also know the true track angle required for computing the wind direction.
GNSS: A Global Navigation Satellite System like e.g. GPS allows precise determination of the aircraft's position. The ground speed can be calculated from the change of this position and the true track is simply the direction of change. A more accurate determination is possible by measuring the Doppler shift of the signal (thanks to bogl for pointing this out).
ADIRS: An Air Data Inertial Reference System as installed on airliners knows the aircraft's attitude and position based on integrating data from accelerometers and gyroscopes. It can be updated via GNSS, but would still provide data for ground speed and track without it.

Modern avionics can display the result of these computations directly:

left: Boeing 737 Navigation display (source), right: G1000 (source)

As far as I know, airplanes just use external data for winds aloft. GPS allows to measure ground speed and true course over the ground, that's good enough.

The closest thing to measuring actual wind speed at altitude is GPS drift in a balloon, or gliding flight computer that detects circling flight (using GPS) and calculates drift.


If pilots in a A320 or 737 had a dual engine failure, would they add flaps for the landing? Would this not be smart to do because you may come in a little fast, therefore the flaps would send you back up? Or would you absolutely want flaps in this situation

Flaps steepen the descent angle - in other words, you run the risk of falling short of the runway. So in a glide you keep the flaps up until you can be certain of making the landing point. Once the landing is guaranteed, you can then deploy gear as well as flap to slow down as much as possible - being aware that these actions will further reduce the gliding range, so constant reevaluation is required.

Yes flaps would be used when landing the 737 with the loss of double engine failure.  A double engine failure landing is an Emergency Procedure. Intentionally landing flaps-up with a double engine failure creates an unnessary Second Emergency.
A double engine failure flaps-up stopping distance may exceed runway length & the speed limits of the tires.
The Airbus flap system is electrical only.
The Boeing 737 flap system is normally hydraulically operated.  In the event of a Double-Engine failure, the 737 flaps can be extended electrically.
A 737 double engine failure landing is similar to a screwed-up parachute landing...there are no do-overs.


In the traffic pattern, what is the appropriate distance from the runway for the downwind leg? Specifically for a piston general aviation aircraft, is there a recommended distance from the runway to fly the downwind leg? Does this change based on the speed of the aircraft?

Most instructors say that (in a low wing plane) you should see the runway on the tip of the wing or between the tip and 1/4 in the wing. AOPA has a nice over view of non towered airports here. This FAA brief states it should be flown 1/2 to 1 mile out (page 7-4 of FAA Airplane Flying Handbook, FAA-H-8083-3B).

  This leg should be
  approximately 1/2 to 1 mile out from the landing runway,
  and at the specified traffic pattern altitude.

If you lose an engine on downwind, you modify the rest of your pattern immediately to keep your aiming point on the windshield at the distance to your landing point. The pattern will no longer be square, but a continuous descending arc that ‘cuts the corners’ and terminates on a very short final to the runway.


What is a 'deep stall' and how can pilots recover from it? West Caribbean Airways Flight 708 which crashed in 2005, fell victim when their plane encountered a deep-stall. From my understanding, only certain planes can 'deep-stall'

How can pilots recover their plane to recover from a deep stall?

A deep stall or a super stall is a condition where the wake of the wing impinges on the tail surface and renders it almost ineffective. The wing is fully stalled, so the airflow on its upper surface separates right after the leading edge, which produces a wide wake of decelerated, turbulent air. Consequently, the dynamic pressure at the tail surface is much smaller than in unstalled flight, which is the main reason for the reduced effectiveness.

Consider this case: The aircraft flies in a nose-up attitude, but on a downward flight path. Consequently, the angle of attack of the wing $\alpha$ is much beyond its normal operating range, causing a fully separated upper surface flow. Due to the T-tail configuration, the wake is hitting the elevator such that all of it is shielded from the regular airflow.

The pitching moment of this configuration over angle of attack (blue line) looks something like this. First there is a stable region with a negative gradient at low values of $\alpha$, followed by a minimum when the wing stalls, and then a region with a positive gradient, where the separation unfolds and the tail moves into the wake from above. This region is unstable in pitch, so without control input the aircraft will not stay there, but either pitch down or up until it reaches a stable region again. At high angles of attack follows another stable region with a negative gradient:

Note that we have two trim points, one in the regular range of the angle of attack, and one way out to the right. In both cases the aircraft has a stable trim condition, so small disturbances are answered with force changes which will keep the aircraft at one of these points. Between the two, there is another equilibrium point, but here the airplane is unstable. If it pitches up slightly there, the pitch up will accelerate until it reaches the upper trim point.

Now consider the control power of the horizontal tail. When it flies in undisturbed air, it can trim a wide range of angles of attack. In the deep stall condition, however, its control power is much reduced, resulting in a much smaller range of trimmable angles of attack. If the lower end of this range is right of the point where the pitching moment crosses into positive values (here at $\alpha$ = 24°), the aircraft cannot escape with elevator deflections!

Please note that the control power is not sufficient to enter the deep stall with quasi-stationary trim changes. The pilot needs to pitch up quickly and has to overshoot the static trim range in order to cross into the stable region above 30° angle of attack. There, his range of trimmable $\alpha$s is too small to achieve the same overshoot backwards.

To get out of this trap needs other changes: Either shift the center of gravity forward, or try to drop one wing. Unfortunately, both the ailerons and the rudder will also be much less effective due to the massive separation and the wake. In a number of cases, even experienced test pilots could not escape this condition.

Deep stalls appears not only for the T tails aircraft. The CG far back will certainly be a good reason to have one of this type of stall. Nowadays the fighter jets are prone to get into the deep stall state. Recovery is done by pushing the nose down and power up.


What if an airspeed prescribed by a published procedure isn't safe for a particular aircraft's operations? Departure and arrival procedures often prescribe airspeeds which must be maintained at certain fixes. 14 CFR 91.117 sets rules for airspeeds but has a paragraph which states that the airspeeds don't apply if the aircraft can't operate safely within those limits. Does any regulation or published recommendation alleviate aircraft from the airspeeds prescribed on instrument procedures for similar reasons?

If you are unable to comply with a published procedure, you simply inform ATC and the controller will tell you what to do instead. The controller will most likely be authorized to make this decision, even if there is no written regulation covering the specific case.

From the same regulations:

  § 91.3 Responsibility and authority of the pilot in command.

  (a) The pilot in command of an aircraft is directly responsible for,
  and is the final authority as to, the operation of that aircraft.

  (b) In an in-flight emergency requiring immediate action, the pilot
  in command may deviate from any rule of this part to the extent
  required to meet that emergency.

  (c) Each pilot in command who deviates from a rule under paragraph (b)
  of this section shall, upon the request of the Administrator, send a
  written report of that deviation to the Administrator.


Can light GA aircraft implement fly-by-wire technology? Theoretically, I know it is possible. I know the benefits of fly-by-wire too.

My question(s) most revolve around:

why it hasn't been done?
What challenges1 would there be?
What benefits are there by not implementing it even for new light GA aircraft2 being produced?
I know that many smaller airplanes (e.g. Cessna 172) do have fly-by-wire flaps. Why the remaining flight controls don't use this technology?

1: Not considering money as an issue.
2: I couldn't find any reference of it for Cessna Skyhawk.

There are multiple factors here:

The first and main one is of course weight. Fly-By-Wire requires computers and hydraulics to actuate the surfaces in a small plane weight is critical and a FBW system may be the difference between 3 and 4 passengers in total capacity.

The next that comes to mind is certification, I'm not sure exactly how this works but I would think that FBW implementation in a current airframe would require a recertification of sorts. With that being said many GA planes flying out there like the 182, Piper Arrow and other similar things still made today are sporting designs first flown more than 30 years ago. It's a simple matter of, "if it ain't broke don't fix it".

I would think that basic service and maintenance would also become more complex and worst of all more costly. I don't know much about the cost of these systems so I wont comment father than speculation like this.

There is a safety concern in small planes (and I'm sure even bigger planes) if control feedback is not present. This Article outlines some serious concerns with the Cirrus side stick and its lack of feedback (not fly by wire but some of the ideas carry over to the FBW systems that don't have feedback).

A Note on the 172:

The way I understand FBW leads me to think the 172 does NOT have FBW flaps. While they are electronically actuated I consider FBW (and by definition):

  ...flight control computers determine how to move the actuators at each control surface to provide the ordered response

There is no computation done in a 172's flaps to my knowledge, if you move the switch they will move. While the flaps are not directly cable driven I would consider the lack of computer to keep the 172 out of the FBW category but thats just personal opinion.

Also of note, the 172 did not always have electronic flaps - that was a later addition to the aircraft in '65.

A Note On Cost:

Although you note that one must ignore cost in this case you really can't. A FBW system would make a GA plane even more expensive than they are. This is a very real and very limiting factor in aviation. With an unlimited budget you could develop, certify, and regularly fly a FBW small plane that was chock full of gadgets but the FAA approval process is what it is and cost is a very real limit for aircraft makers.

It is actually technically possible to implement FBW in light aircraft. Technologies like Horizon Hobby ASX, SAFE & A3D already provides a FBW for RC planes, drones and helicopters. Likewise, the drones like DJI do have "follow me" mode where the drone is able to follow a person on bike or on foot at a set altitude and attitude. So, technically, it is possible. It's already implemented there. Just need to find some GA aircraft producer to bite the bullet and get these stuff and certificate and integrate in their products.
By the way, with FBW, you generally use electric servo motors, not hydraulics for control surfaces.


Why does the B-2 have a smaller payload than other bombers of comparable size? B-2 Spirit1

Payload
40,000 pounds (18,144 kilograms)
Wingspan
172 feet (52.12 meters)
Weight
160,000 pounds (72,575 kilograms)
Maximum takeoff weight
336,500 pounds (152,634 kilograms)
Range
approximately 6,000 nautical miles (9,600 kilometers)

B-52 Stratofortress2

Payload
70,000 pounds (31,500 kilograms)
Wingspan
185 feet (56.4 meters)
Weight
Approximately 185,000 pounds (83,250 kilograms)
Maximum takeoff weight
488,000 pounds (219,600 kilograms)
Range
8,800 miles (7,652 nautical miles)

B-1B Lancer3,4

Payload
75,000 pounds (34,019 kilograms)
Wingspan
137 feet (41.8 meters) extended forward, 79 feet (24.1 meters) swept aft
Weight
approximately 190,000 pounds (86,183 kilograms)
Maximum Takeoff Weight
477,000 pounds (216,634 kilograms)
Range
5,100 nmi (5,900 mi; 9,400 km)

The US Air Force web-site says:

  The revolutionary blending of low-observable technologies with high aerodynamic efficiency and large payload gives the B-2 important advantages over existing bombers.

But in comparison with the other bombers, including much older B-52, it appears to be less aerodynamically efficient and carries less payload.

Why does the B-2 carry a much smaller payload than the other bombers of comparable size? Does it signify, that B-2 has worse aerodynamic characteristics? If yes - what are causes of it?

The simple answer is that it is optimized for being low observable/stealthy, and long range, rather than for maximum payload.

When you design an aircraft, you make a variety of trade offs depending upon which features are most important for that design.  The design of the B-2, which reaches back into the 1980's1, put a premium on the ability to avoid being detected by radar.  This informed the shape.  The USAF's strategic purpose for that aircraft was to enable it to reach globally, so that it could be launched form the continental US or a forward deployed base.  This put a premium on range/fuel capacity.

@Durandal points to another detail/difference: The B52 and B1 both can carry ordnance on external hard points (and this is a must to get up to the cited payloads). The B2 has no such hard points because it would nullify its stealth capability. There is simply no room to put more munitions within the bomb bay.

With the advent of precision weapons, which were in parallel development to the B-2, the raw tonnage wasn't as important as getting to the target area, and getting out "without being seen."

Because aircraft are all constrained somewhat by the cube/square law in terms of size, the trade offs/compromises on that model arrived at a payload that fit in with the rest of the requirements.

Both the B-52 and B-1 were build under a different design paradigm, under different requirements combinations, and were "pre-stealth" bombers: the B-52 was meant to get the most range and raw payload together, while the B-1 combined speed (supersonic, back when speed was perceived to be at a premium) and payload foremost.  While both have since benefitted from the use of precision munitions, the original designs (all nuclear weapons carriage considered) had to account for the problem of non-precision munitions shortcomings with accuracy.  (Experiences in WW II informed this problem, as did experience in Viet Nam).  You need to drop a pattern of "x many bombs" to have a high probability of hitting a given target.

1 Insofar as the "flying wing" idea for the shape of the B-2, the initial attempts in that direction go back to the 1930's and the Ho_229 as so @paracetamol kindly reminds us.  Also, and FWIW, it is related to a DARPA  project that goes back to the 1970's (stealth / radar resistant in general) that was compromised publicly by President Carter during a press conference.  Actually, those paying attention had heard of it from Kelly Johnson: In fact, that existence was far from secret. On July 23, 1976, readers of Aerospace Daily were informed that Clarence L. (Kelly) Johnson, "the nation's premier aircraft designer" and architect of the U-2 and SR-71 spy planes, was bulding "a new 12,000-pound, one-man Stealth aircraft" at the Lockheed plant in Burbank, Calif. The magazine claimed that the $90 million program, sponsored by the Defense Advanced Research Projects Agency, was designed "to reduce aircraft visibility -- optical, acoustic, and radar signatures -- through new technology."

There is another possibility - Neither the B52 nor the B1 has had information on it restricted to the degree that the B2 has.

It may well be that the B2's actual payload is quite a bit higher than has been publicly acknowledged. A great deal about that aircraft is still considered highly classified.


What is the dark spot visible below the cockpit on A-10s? On most A-10s I have seen, the area under the cockpit is darker than the rest of the plane. Is there a reason for this?

It's a false cockpit, a type of camouflage patented in 1980 by Keith Ferris, a US artist and camouflage designer. From some angles, it makes it difficult to determine the orientation of the aircraft. The Canadians were the first to apply it; pictured is a CF-18 Hornet with one:

Notice how at a glance, it takes a second to realize the Hornet is inverted and pulling towards the ground. During dogfights this can be enough to make opposing pilots think the aircraft is going a different direction. It might not seem like much in a photo, or if you're watching an aircraft fly past at an air show or airport. In the stress of combat while pulling extra Gs it's more than enough to confuse or delay a reaction.

For the air to ground mission, this is particularly important. If an A-10 encountered antiaircraft fire or an enemy aircraft it would have to rely on its own agility to escape or gain the upper hand. Other nations have adopted this technique — I've seen French and Russian types, and possibly Gripens of some air force. As far as I know, the A-10 is the only US aircraft regularly camouflaged in this way.

There was an article on this in Aerospace magazine way back in the late 1980s (I still have a photocopy somewhere).

They called it Visual Stealth. The article included the long history, including
using lights to illuminate the darker regions of aircraft when viewed from the ground.

One picture I saw clearly showed a 'tail shadow' painted on the bottom
of an F16. False cockpits were common, as were painting the tops and bottoms
different colors. Ground Strike aircraft would commonly have yellows and
brown camouflage, white in the winter (Germany). The Navy was using blues and
grays, with the tail squadron markings rather dull.


For electric aircraft, is MTOW = Empty weight + Maximum payload? Electric aircrafts and most drones have simple powertrains, and their weight does not vary along the flight. After reviewing this thread I assume that:

MTOW = Empty weight (batteries incl) + max payload ?

I have reviewed some drone specs, and sometimes the numbers match, others don´t. Am I missing something?

A maximum payload may be specified to be less than tested MTOW minus empty weight in some cases, as a precaution against conditions that may reduce MTOW -- which depends on strip elevation, barometer, and temperature.

The thinner (higher and hotter) the air, the less a given amount of power can lift, in the case of a quad-copter or similar aircraft, or the longer it will take to reach takeoff speed and the slower climb will be, in the case of a conventional winged drone (electric or otherwise, though at least electric motors don't lose power with altitude).  Responsible drone manufacturers may (and should) specify a maximum payload spec that will keep gross weight below the least MTOW for foreseeable conditions.

There may also be cases where, for one reason or another, payload is based on testing conditions different from your flight configuration -- for instance, if you're using a heavier battery pack than the one used for testing, you'll have less margin below MTOW than the test condition.  Payload limits may also be specified below MTOW minus empty weight for reasons of center of mass location, payload restraint limitations, or other engineering reasons.

There is a difference between MTOW and the actual weight of the aircraft and payload. MTOW, or Maximum Take/off Weight, is the amount of weight the aircraft is certified to carry on takeoff. 99.99% of the time, the actual weight of the aircraft and payload is lower than the MTOW. But I think you know this. I think what you meant was does the MTOW include the empty weight, or is it just maximum payload.

In that case, yes, MTOW does include both the MAXIMUM payload and the EMPTY WEIGHT of the aircraft (including electric).


What is defined as "day VFR" under EASA rules? I received a document where it it specified that the flight relevant for such document can only take place in "Day VFR" conditions undear EASA regulations.

Is this connected to VMC? What does EASA defines as "Day VFR"?

It's by opposition to Night VFR (NVFR) which allows to fly by night in visual meteorological conditions. So the answer will focus on NVFR, rather than on day VFR.

EASA harmonization over EU countries is done by enforcing Standardised European Rules of the Air (SERA). SERA states that a night flight must be conducted in IFR, and therefore the crew must hold an Instrument Rating.

Prior to SERA, some countries did not allow VFR at night for security reasons (aircraft not visually identifiable, and no transponder), but other did, that's the case for the UK that I'll use as an example here.

When implementing SERA, EU countries can use acceptable means of compliance, as described in ED Decision 2013/013/R and its annex.

NVFR is implemented (or denied) in EU country by country. So rules may differ between countries. UK example:

UK license can be extended for NVFR.
More for UK NVFR: Safety Notice: SN-2012/007.
In practice, VFR at night is permitted in accordance with SERA requirements. Aircraft leaving the vicinity of an aerodrome must maintain 2-way communication with ATC and file a flight plan. The process of 'booking out' is still accepted as an alternative method to filing a formal paper or electronic flight plan in certain circumstances. Similarly, abbreviated flight plans filed in flight are still permitted. There are also more restricting weather minima:

Minimum cloud ceiling of 1500 ft AMSL
Flight visibility of 5 km, or 3 km in the case of a helicopter flying outside controlled airspace
Maintain sight of the surface when flying at 3,000 ft AMSL or below
Minimum height of 1000 ft (or 2000 ft if over high terrain) above the highest fixed obstacle within 8 km of the aircraft except when taking off or landing

Night is defined for  this purpose:

e.g. for UK in Air Navigation Order 2009 Art. 255:

  'Night' means the time from half an hour after sunset until half an
  hour before sunrise [...] at surface level.

Aircraft must be compliant for NVFR, e.g. this equipment is required:

artificial horizon
Instrument Lighting
Landing Light
Position and Anti Collision Lights

In countries where NVFR is not allowed, IFR applies at night.

VFR @ night in Germany requires a HG and DG, VSI, - a standard IFR panel plus a VOR receiver, lights and License. The funny description for the beginning of night applies here too. The German Weather Service makes these times public for selected airports. Choose the one closest to yours. See this link (in German).
Else a flightplan is required and communication to radar.
IMHO all overly too many requirements. VFR @ night is not so much more demanding as VFR/day on a hazy day. Considering it IFR because of the "lack of a horizon" shows that these rules are made by folks who never flew at night, or even never flew.


How does the IAS stall speed vary with increasing altitude? First of all, we all know what IAS is and if not for some people you can follow this link to read the basics about stall and the differents speeds. So we also know that our TAS/ Mach number will increase with increasing altitude.

Let's assume that our IAS stall speed is 100kts at sea level, what will be our IAS stall speed at 30 000 feet with exactly the same aircraft ? (Assume ISA atmosphere)

Everyone would be tempted to answer that it doesn't change, right? but what about the low speed buffet in this picture ?

We agree in saying that the low speed buffet here is not the same as the one at sea level but look, our IAS/CAS stall speed has a higher value now. Maybe that it's a representative value of IAS/CAS calculated by the Air Data Computer from an EAS but still, our IAS stall speed has rised.

We can also keep it simple and think about it for a non pressurized single engine aircraft. I don't need an exact value but I would love to have a logic and smart answer.

It seems to be very basic but when we correctly think about it we can find ourself a little bit confused.

For me, the answer is : The IAS stall speed will increases

Airplanes do not stall at the same indicated speed or even at the same angle of attack - it all depends on circumstances.

The angle of attack dependency is discussed here. An increased pitch rate can push the stall angle of attack 50% higher than what the stall angle of attack is in stationary conditions.

The next big factor is the Mach number. When increasing the angle of attack, the flow around the airfoil's nose will develop a suction peak. This suction is equivalent to higher local speed, and if the critical speed (when local flow speed equals the local speed of sound) is exceeded, the flow past the suction peak will no longer behave similarly to the flow at the same angle of attack but a lower flight Mach number. Let's just say that the local Mach number in the suction peak has a strong influence on the stall angle of attack, and flying at a higher Mach number lowers the stall angle of attack, sometimes dramatically.

Increasing altitude will raise the flight Mach number in two ways:

The reducing density means you need to speed up to fly at the same dynamic pressure, and
the atmospheric lapse rate decreases the speed of sound in air.

Both effects conspire to reduce the stall angle of attack at 30.000 ft to a value quite a bit below that at sea level. Details depend on the airfoil and specifically on its nose radius and wing loading.

Only very light aircraft will not be affected by the change in Mach number, but even here the stall angle of attack at altitude is lower than at sea level due to the reduction of the flow's Reynolds number with increasing altitude.

In short, the indicated stall speed goes up with increasing altitude for a variety of reasons and does so nonlinearly. The magnitude of the change depends on a multitude of details.

Vstall is measured as a true airspeed, it increases approximately 1% for every thousand feet increase in altitude.
100KTS its sea level - 110 KTS at 10000 feet
TAS increases 2% per thousand feet for any given IAS.
110 KTS TAS at 10000 feet  = 92 kts
Thus, Vstall TAS increases, IAS decreases


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.

Flows are basically ways to avoid doing checklists. If you use a checklist you do not need a "flow" because the checklist determines the order of items to be checked so a "flow" is completely superfluous. The "flow" is just a way of checking things ad hoc without using an actual list to save time.

The reason why commercial pilots use "flows" is because if they used a checklist for a lot of activites (which they should do) it would take too much time. Seriously, do you want 300 people waiting at the gate and leaving 20 minutes late because the pilot is still working through checklist number 7 and making sure the backup oxygen tank is pressurized or whatever? Using "flows" becomes a matter of practicality.

Where flows become really dangerous is on those private jets where some arrogant CEO is demanding they take off "right now" and the crew starts doing "flows" and skipping checklists. A perfect example is the Gulfstream IV crash last year that killed Lewis Katz, some media mogul, and six other people. The pilot failed to disengage the elevator gust lock. That's the kind of thing that happens when you start doing "flows".


Can pilots take multitools on board in Canada? Can pilots in other countries or Canada carry Swiss army knives onboard on commercial flights? Passengers are not allowed to do that in Canada.

pilots are never allowed to have any kind of weapon on board. when pilots go to work they have to go security just like the passengers.

there has been accidents because of this.
https://en.wikipedia.org/wiki/Federal_Express_Flight_705#Flight_crew_and_hijacker

its maybe allowed when the total length is smaller then your hand but i`m not sure if this rule applies to pilots.


Why are critical flight computers redundant? At least in airliners, the truly critical computers are redundant. Typically three identical copies of the autopilot computers run in parallel and compare results; if one computer disagrees with the other two, its output is ignored. The system allows some processors to be faulty while maintaining the operation of the overall system.

But why? I've never heard of microprocessors suddenly failing. Sure, there could be manufacturing errors, but those would have been caught at the factory. Perhaps the program (and its proof) is wrong, but it would be wrong in the same way across the processors. Similarly, bad input would cause bad output across all three computers. What kind of errors does this redundancy protect against? Do microprocessors sometimes just do math wrong?

If a microprocessor is overheated or overloaded and spontaneously fails, I would expect it to stop doing anything and produce no output. To deal with this kind of failure, you'd want to have a backup processor, but you wouldn't need to compare the outputs of three computers—any output produced would be assumed correct, so you'd be happy to directly use the output of any processor that was producing output.

Related: The answer to What is the purpose of multiple autopilots? simply says "redundancy" before going into how this is achieved.

Failure modes to consider:

Overheating. This changes the chip's timing properties and eventually results in error. This can manifest as single-bit errors in the middle of seemingly normal operation; it will eventually crash, but may output bad data first.
Water damage. Manifests as a parasitic resistance on the board and may cause you to misinterpret bits as high or low. May be leaky housings, condensation, etc.
Electromagnetic interference. (The system is supposed to be resistant to this, but it's still worth thinking about).
Physical connection problems. Either during construction (soldering faults) or induced afterwards (heat, vibration). Microscopic cracks in boards or joints can pass QA but result in intermittent faults. Again this can lose you a single bit at a time. This is related to the Xbox "red ring of death" issue.
Failure of other components. Capacitors are the usual suspect; electrolytic, tantalum, ceramic all have different failure modes. Again this may result in a system that mostly works but is prone to misinterpreting marginal values or suffers from timing drift.
Weird materials science ("Purple plague", tin whiskers due to lead-free solder)
Part QA may not be up to the standards you expect (suppliers shipping inferior parts with a bogus "aerospace grade" label). Hard to detect even after it's happened.

It's important to recognize that in high-speed digital systems you don't get nice clean "one" and "zero", you get a series of rising and falling edges that are smeared out by the parasitic capacitance and inductance of the wiring. This is inherently vulnerable to being misinterpreted in marginal electrical conditions.

Because, despite the theory being good, the reality is that not all computer components are equal.

A specific example from the early 90s: Intel produced the 486/33 CPU (it was quite cutting edge and blazingly fast for the day). Most left the factory just fine, but some had an esoteric bug in the FPU that would generate incorrect answers. The magazines of the day were filled with calculations you could put into your spreadsheet that would produce X if your CPU was good, or Y if it had the bug.

If your plane happens to be running with one of the faulty CPUs in it, and just the right set of data happens to be collected and fed into any of the flight control programs and runs into this FPU bug, you'll be happy that the other two CPUs calculated the correct value and kicked the errant one out of the loop.


Airline safety: what happened between 1959 and 1962? The graph on page 17 (PDF page 18) of this Boeing air safety publication shows the fatal accident rate for commercial jets in the US and Canada dropped from about 40 per million departures in 1959 to 2 per million departures in 1962.  Since then, the rate has declined even further, but nothing as dramatic as the original drop.

What happened during the the 1959-1962 period to so greatly reduce the accident rate?

I believe the answer has something to do with the introduction of the passenger jet airliner, which first came into service in the late 1950s.  Note please that the original poster is asking for information on "commercial jets" whereas the statistics that others have offered have information on commercial planes in general, including prop planes.  I glanced at the statistics for 1959 presented above and there were only two passenger jets (including one KC-135, which you may discount if you like) that crashed.

Compare this to the statistics presented for 1962.  There were six or seven crashes of Boeing and Douglas jet airliners.

To me this means the differences were in all probablility not statistically significant.  We don't have enough "samples" to reach a valid conclusion.

What you can see is a general explosion in the number of people flying.  Jets really introduced the public to flying.

When you are looking at "per capita" style numbers you also have to look at the overall volume in your population. Given that the time period is the general start of the growth of aviation, I'm going to guess that you would find that overall flights (and passengers, miles, etc, etc) increased during the same period. That would make the "per X" number of virtually anything you look at in aviation improve.


Is it legal to give flight instruction in my own airplane without 100 hour inspection if doing it for no charge? 14 CFR §91.409(b) states

  ...no person may give flight instruction for hire in an aircraft which
  that person provides, unless within the preceding 100 hours of time in
  service the aircraft has received an annual or 100-hour inspection and
  been approved for return to service in accordance with part 43 of this
  chapter or has received an inspection for the issuance of an
  airworthiness certificate in accordance with part 21 of this chapter.

What if I want to give instruction to a friend or family and they are not paying me to do it? Would I be exempt from having to do a 100 hour inspection?

I agree with acpilot that if you're merely renting the plane to this pilot then no 100hr is required. Rentals are not "for hire" operations.

I do that with a Cherokee that I rent out. I don’t provide the CFI and I do not fly it for others. Several students have taken their practical tests in the plane and I made sure they could explain the FAR to the DPE and they had no problems.

As several commenters have stated, it gets tricky when you own the plane and provide instruction. The FAA considers lots of things as compensation that you and I would not. Goodwill, logging flight time, paying for gas, or even paying for lunch or a beer.

I found a clarification letter from the FAA at Aviation Banter.
http://www.aviationbanter.com/showthread.php?t=11563&page=2

May 3, 1984
Mr. Perry Rackers
Jefferson City Flying Service

Dear Mr. Rackers
This is in reply to your request of May 1, 1984, that we render an opinion regarding the applicability
of the 100-hour inspections requirement of Section 91.169(b) of the Federal Aviation Regulations to rental aircraft.
Section 91.169(b) of the Federal Aviation Regulations provides that, except as noted in Section 91.169(c),
a person may not operate an aircraft carrying any person, other than a crewmember, for hire, and may
not give flight instruction for hire in an aircraft which that person provides unless, within the previous 100
hours of time in service, the aircraft has received either an annual or a 100-hour inspection.
If a person merely leases or rents an aircraft to another person and does not provide the pilot, that
aircraft is not required by Section 91.169(b) of the Federal Aviation Regulations to have a 100-hour i
nspection. As noted above, the 100-hour inspection is required only when the aircraft is carrying a
person for hire, or when a person is providing flight instruction for hire, in their own aircraft.
If there are any questions, please advise us.

Sincerely,
/s/
Joseph T. Brennan
Associate Regional Counsel

One correction to acpilot about the 100 hours. Once you start renting for hire, you need to do an inspection every 100 hours. The clock doesn’t restart every time you do the inspection or annual. You are allowed a little leeway to ferry the plane to the inspector, but you don’t reset the clock.
The 100-hour limitation may be exceeded by not more than 10 hours while en route to reach a place where the inspection can be done. The excess time used to reach a place where the inspection can be done must be included in computing the next 100 hours of time in service.

If the CFI owns the plane then he must have a 100hr done even if the instruction is "free" in the sense that the student pays nothing.  However, in the eyes of the FAA, flight time is compensation so the flight will not have been "free" in the context in which you are posing the question.  You will have been compensated in dual-given flight hours even if you bear 100% of the cost.  If you own the plane and have had an annual performed in the last 100hrs, you're good to go.  Now, if you're merely renting the plane to this pilot then no 100hr is required.  Rentals are not "for hire" operations.  You can fly along with your friend but you cannot legally log hours.

If the student owns the plane and hires you then no 100hr is required (the way I read it).

Link to the FAA regulation (as of 13 July 2016): http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFar.nsf/FARSBySectLookup/91.409

Link to another helpful article: https://blog.globalair.com/post/When-is-the-100-Hour-Inspection-for-Aircraft-Used-for-Rental-and-Flight-Instruction.aspx


When crossing a mountain ridge at low height above terrain what consideration is given to turbulence? Some background: I am not a pilot, but a researcher studying air-flow across mountain terrain using Computational Fluid Dynamics (CFD).

During my studies, I have been particularly interested by high-altitude ridges (2 to 3000m a.s.l., say 10000 ft) that are exposed to regional winds that are generally across the ridge. I have been seeing very interesting turbulence patterns above, and in the lee of the ridges (rotors).

Here is the question: what instructions are given to pilots needing to cross such a ridge at low heights above the terrain, in either direction relative to the wind? What does common sense dictate?

I am naturally thinking mostly of helicopter pilots doing mountain work, but any other aircraft are very welcome (fire-fighters, ULMs ...).

From an older FAA Publication on mountain flying:

Mountain Wave
When the wind speed is above about 25 knots and flowing perpendicular to the ridge lines, the air flow can form waves, much like water flowing over rocks in a stream bed. The waves form down wind from the ridge line and will be composed of very strong up and down drafts, plus dangerous rotor action under the crests of the waves. If enough moisture is present, lenticular clouds can form to give a visual indication of the wave action. These clouds are reported in the remarks section of hourly sequence reports as ACSL (altocumulus standing lenticular) or CCSL (cirrocumulus standing lenticular)

Pretty much sums up what you're seeing I guess. As for action:

Ridge and Pass Crossing
On most mountain flights, you will need to cross at least one ridge or pass. Experienced pilots recommend crossing a ridge or pass at the ridge elevation plus at least 1,000 feet. If the winds at mountain top level are above 20 knots, increase that to 2,000 feet. Plan to be at that altitude at least three miles before reaching the ridge and stay at that altitude until at least three miles past it. This clearance zone will give you a reasonable safety zone to avoid the most severe turbulence and down drafts in windy conditions.
If conditions or airplane performance dictate, you may need to fly along the windward side of a ridge to find updrafts for gaining altitude before crossing a ridge. You may also need to circle before reaching the ridge if climbing out of a valley airport. When you actually cross a ridge, you should do so at a 45• angle to the ridge. This allows you to turn away from the ridge quicker if you encounter a severe downdraft or turbulence. Once you have crossed the ridge, turn directly away from it at a go• angle to get away from the most likely area of turbulence quickly. Plan your crossing to give yourself the ability to turn toward lower terrain
quickly if necessary.

As for helicopter mountain flying specifically, I'm afraid you are unlikely to find somebody on here with that experience. You might have better chance on searching for it online and phoning up flight schools that offer such courses (I found a few in the states) for information.

Yeah, the instructions are DON'T GO NEAR ROTORS OR YOU MIGHT DIE.

You never want to pass close over a ridge, even if does not have lenticular cloud or other visible sign of downdraft. Once you get caught in the down draft it can be almost mathematically impossible to escape. My instructor's instructor was killed in Maine by trying to cross a mountain too close.

The procedure is to navigate to a valley or pass where you can clear the mountain by a healthy margin.


Why don't all commercial aircraft transmit GPS data in real time? It seems strange that trucks and taxis can be set up to transmit GPS data in real time but aircraft cannot.  Wouldn't this be a useful function and feasible to implement?

Most commercial aircraft transmit their GPS-based position twice per second. This is part of their Automatic Dependent Surveillance – Broadcast (ADS–B) broadcasts. The problem with providing world-wide receiver coverage for this system is that the frequency it uses only travels line via line of sight, so it won't travel past the horizon.

Providing coverage over large bodies of water would require a network of buoys, which would be quite expensive.

Another possibility is to put ADS-B receivers on satellites. This concept has been developed by (Aireon) on the Iridium Next satellite constellation. The system (66 satellites + 9 spares) became operational in 2019 and provides global coverage.

Consider that radio line-of-sight horizon varies with altitude and transmission power.  I have not calculated the radio line-of-sight horizon from 30,000 to 35,000 feet but I imagine that it is staggering.

There are Ham radio operators listening for distress calls twenty-four hours a day, around the world. A distress call accompanied by GPS coordinates would get immediate attention from anyone on the frequency. Ham satellites are another resource.


Why do we feel gravity on a plane? How come a plane flying at constant velocity experiences gravity?  If you were in a space capsule flying (not accelerating) you would feel weightless until you hit the ground.  Why not a plane?

This is the difference between flying and in orbit. In orbit, you are indeed falling toward the earth, but the spacecraft is too, and you're going fast enough that you keep missing the earth.

In an aircraft, because it's staying aloft due to lift, it is not falling. This is why you experience the pull of gravity on a plane.

Some aircraft are designed to feel weightlessness, see Vomit comet.

Newton's Cannonball.

https://en.wikipedia.org/wiki/Newton%27s_cannonball

In a plane, you're the cannonball marked "A", and the only thing stopping you from plummeting straight into the ground is the lift generated by the wings.


Can a "Destroyed" Helicopter be repaired and flown? If a helicopter is reported by the NTSB as Destroyed in their Accident report, and as they make no disposal recommendation in their reports, can the aircraft be legally rebuilt by an authorized and approved FAA and Bell Repair facility and flown again?

Follow up:

The aircraft in question, after using Bell referenced repairs, carried out by a Bell Licensed Repair facility, in a Bell Certified Jig, now has its Certificate of Airworthiness and is again Supported by Bell and has a handsome price tag.

The NTSB defines Destroyed as

  Damaged due to impact, fire, or in-flight failures to an extent not economically repairable.

Another common definition is:

  The estimated or likely cost of repairs would have exceeded 50
  percent of the new value of the airplane had it still been in
  production at the time of the accident.

This fact that the costs of repairing are estimated to be exceed the economical value of the aircraft does technically not prevent the aircraft to be repaired and made flyable again. It can be recertified on the original airworthiness certificate. See FAA order 8130.2H.
Special attention needs to be given to the identification plate (serial numbers etc.) of the aircraft; the original plates of the aircraft have to be installed.

Do not expect any support from Bell as on their website they state:

  There are some aircraft that have been destroyed in an accident or
  retired from service that are no longer considered to be genuine Bell
  Helicopter Aircraft. These aircraft will not be supported by Bell
  Helicopter.

This makes resurrected Bell helicopters very difficult to sell in the future.

Any aircraft or helicopter listed as Destroyed by either the FAA or NTSB or both, cannot be rebuilt.  Check the FAR's.


Which fixed-wing aircraft has the highest number of required flight crew members? Most modern airliners require two pilots to operate. Older airliners require a flight crew of three: two pilots plus one flight engineer.

Has there ever been an aircraft where the number of required flight crew members is extraordinarily high, for example five or six?

To clarify the question:

"required flight crew member" is the number required by relevant regulations, not the number needed to physically operate the plane. If that number is not met, the plane could not legally have taken off
gunners / weapon operators of military aircraft who are not necessary for a safe flight are not included
flight attendants are not included

The Antonov An-225 Mriya requires a crew of six- you have the pilot, copilot, 2 flight engineers, navigator and a communications specialist/radio operator.

An-225 cockpit; image from sas1946.com


Why did fly-by-wire systems take so long to implement? The first commercial FBW airplane was the Airbus A320, which was introduced in the late 1980s. This system only worked after decades of research by American and European aerospace companies. If FBW only converts mechanical motions from an airplane's control yoke into electrical signals (along with sensor feedback), which change the aircraft's control surfaces, what caused FBW to be implemented so late, besides the abundance of computers even before the A320? Can someone also check my understanding of FBW?

My understanding of FBW:

Aircraft manufacturers use rotary encoders and potentiometers to translate mechanical changes in the control yoke into electrical signals.
The FBW computer(s) use feedback from the aircraft's sensors, and compare it with the pilot's input. A derivative based FLL system is used, perhaps?
Hydraulic valves/servo motors are used by the FBW system to change the state of control surfaces.

Thank you.

A simple answer is that the aircraft control system has ultimate responsibility for survival of the aircraft. If it completely fails, you are as good as dead in most cases. Short of in-flight destruction, hardly anything can be worse.

Thus, full-authority (i.e. without mechanical backup) FBW gained acceptance only when the confidence in its overall reliability was sufficiently high. Naturally, it appeared on military airplanes first, where demands to reliability can be lower (the pilot can eject, after all), while demands to the control system sophistication are often higher.

(Others have already commented that A320 wasn't the first commercial airliner with FBW; Concorde had it much earlier. As for your understanding of FBW, it's basically correct. Sometimes, strain gauges rather than potentiometers are used as control stick sensors: force as the primary input is generally better than displacement).

The first real FBW system was probably the one put on the F16... to increase maneuverability, the aircraft was designed to be unstable in flight, so the FBW was necessary to keep the plane flyable. In that case, there was a compelling reason to develop FBW: a more maneuverable combat aircraft. Also, that system was ported to the F117, which had such atrocious aerodynamics that it, like the F16, was essentially unflyable without computer assistance.

In commercial aviation, the case is far less compelling. And it hasn't been an easy path. The very first A320 ended up landing in a forest, when it's flight computer mistook a slow flyby at an air show for a landing cycle. Oops... There have been several crashes traceable directly to FBW or sensor malfunctions (XL Airways/Air NZ acceptance flight, AOA sensor froze up) and Air Asia 8501, an A320 that crashed due to high altitude stall brought on by a malfunctioning rudder position sensor , to sensor malfunctions combined with different flight control layout, plus maybe fully automated aircraft lulling pilots into complacency (AF447, pitot tubes froze, bad sidestick design, inexperienced pilot), to just plain confusion in the cockpit working with FBW systems (Air Inter confusion setting descent rate, flew into a mountain).

Plus non fatal incidents that could easily have become fatal, like Qantas 72, where the inertial reference unit started sending weird data to the flight computer, sending the plane into a series of uncommanded dives and ascents.

FBW was supposed to make flying simpler, when in truth it just trades one set of complexities for another.

They have been slow in coming in commercial aviation because the advantages to airliners (who don't need more maneuverability or stealth capability) aren't nearly as compelling as they are on military aircraft, while the consequences of failure tend to kill a lot more people. If the FBW computer malfunctions in a military aircraft, the pilot punches out and has about an 85% chance of surviving. Airliners don't have that option.


How does a vertically higher center of gravity affect handling? Much of the discussion of the center of gravity of the aircraft is focused on the longitudinal axis, i.e. front and back. How does the vertical position of the CG affects the handling characteristics?

For example, the Boeing Dreamlifter and the Airbus A300-600ST both have their cargo stored in the upper portion of the airframe. Are these aircraft easier to "flip over"?

As long as flight is coordinated, the vertical position of the center of gravity (cg) is of minor importance. It will show in issues like thrust changes, when acceleration will cause higher trim changes because of the increased lever arm between the inertial forces and the thrust forces.

This will only change when flight is no longer coordinated and the aircraft sideslips. Now the big cargo volume is more important than the cg location because it will contribute a considerable side force. Also, it will need additional means of lateral stabilisation because the big fairing will destabilise the aircraft in yaw. Still, the lever arm between the cg and the lift force vector will be much, much smaller than the lever arm of the ailerons, and a little aileron deflection will be enough to stabilise the aircraft.

Maneuvering will look funny to crews used to fly the unmodified version of the same airplane, because now a roll manoeuver will induce a lateral motion at the location of the cockpit which was not there before. Same goes for eigenmodes like the Dutch roll which will be more noticeable for the crew because their cockpit sways laterally.

"Flipping over" needs deliberate commands from the pilot; this is no different in aircraft with unusual vertical cg positions. The most extreme is probably the VM-T "Atlant" version of the Russian M-4 Molot bomber.

M-4 Molot version VM-T Atlant with Buran booster tank (picture source)

Most airplane designs take advantage of the CG vertical offset wrt the center of lift to help auto pitch the plane with overall configuration of wings and elevators and engine's thrust.

You get auto pitch up when you add to thrust of engines and vice versa you get nose down by reducing power. Im emergencies this is the only last resort of controlling the pitch.
An easy way of imagining this is to think of the plane as hanging from a long string: add more power it pitches up; reduce power it pitches down.

Each plane design has a manufacturer's design volume inside which CG will create acceptable moment arm to safely control the plane and fly it. Many crashes have happened because of violating this limitation. In Cargo planes there are loading charts and anchors prescribing where and how to lock in tall loads or how to distribute loads in cargo space.

Handling of a plane with higher CG requires more carful control of coordinated flight to prevent potential wild banks or stall of one wing in turns.


Flying in a helicopter with open doors: why don't people fall out? This has been puzzling for quite a long time.

Every action movie or military documentary features helicopters with no door or with open doors and yet people inside look like they couldn't care less. Apparently they're not falling out...

Why is it so?

Aircraft, fixed-wing or rotorcraft, have limited capability to produce a sideways force, so they simply can't throw you out.

It is a matter of physics. Inertial forces (gravity and centrifugal force) act on you and the aircraft the same, so they won't make you move relative to the aircraft. The only force between you and the seat is caused by the aerodynamic forces. And the wing or rotor can only produce significant force vertically, and some torque with help of control surfaces. But for lateral force there is only drag of the fuselage and the vertical stabilizer and, in most helicopters, anti-torque rotor, which don't produce that much force unless there is really bad turbulence or in some cases if the handling is really bad.

When aircraft turns, it banks to be able to produce the necessary side force, so the resulting force is still mostly straight to the floor.

Of course the other reason is that all aircraft and helicopters have seat-belts and the people sitting by open door usually have them on—except for skydivers, who have the parachute on already, and rescue divers who are tied to the winch instead.

Take a bucket of water with a handle. Start swinging it in a pendulum motion until it has enough swing to actually go around at the same constant speed. Not a drop of water will be spilled. #Pendulumeffect


Is there any regulation to ensure that life jackets and safety cards are on-board? On many flights, I was told that a life jacket is under my seat and safety card is in the pocket in front. Is there any regulation that ensures that life jackets and safety cards are on-board on all flights?

The FAA has a similar requirement (commercially under part 121)

  (a) Except as provided in paragraph (b) of this section, no person may
  operate an airplane in any overwater operation unless it is equipped
  with life preservers in accordance with §121.339(a)(1) or with an
  approved flotation means for each occupant. This means must be within
  easy reach of each seated occupant and must be readily removable from
  the airplane.

  (b) Upon application by the air carrier or commercial operator, the
  Administrator may approve the operation of an airplane over water
  without the life preservers or flotation means required by paragraph
  (a) of this section, if the air carrier or commercial operator shows
  that the water over which the airplane is to be operated is not of
  such size and depth that life preservers or flotation means would be
  required for the survival of its occupants in the event the flight
  terminates in that water.

In other words they are only actually required (per FAA regulations) when operating over water so not every plane (route provided) technically needs them. However many airplane seat bottoms may double as a personal flotation device so many planes are equipped with them by the nature of their construction.

User11933, has reproduce the legislation refering to those specific items.To answer your other question ie:who checks it.The flight attends do, in theory. After each flight they are supposed to check and make sure none is missing.It is part of the equipment of the aircraft and as such, listed in the MEL.(Minimum equipment list) which is the document listing all the systems and equipment mandadory on board.
Obviously the captain is ultimately responsible. On smaller aircrafts with no FA, it is actually up to him or to the FO by delegation, to make sure they are on board before departure.
Hope that clears it up :-)


Why don't Russian aircraft sell as much as their European/American counterparts? Are there any reasons other than political why Russian jets don't sell?

For a case study, let's compare Sukhoi Superjet and Mitsubishi  Regional Jet. Despite being delayed several times, Mitsubishi has secured more orders than Sukhoi. Similarly, Embraer and Bombardier aircraft sell much more than the Sukhoi Superjet. Many new airlines continue to go to with Embraer and Bombardier. Despite promising lower running, maintenance, purchasing costs, why doesn't this aircraft secures orders?

If you take out the political angle (which is by far, the most important), there are a number of reasons for this.

Basically, the Russians have a serious image problem. Russian (and Soviet) aircraft have a reputation for poor quality, reliability and safety issues. This will take a long time to fix. In contrast, Japanese have no such problems (In fact, the MRJ boasts of 'legendary Japanese reliability')
It is not easy to make airlines switch from an existing aircraft. Most airlines have a huge system built around the aircraft they operate (In fact, quite a few regional carriers operate only a single aircraft type). It would take enormous amount of investment in time and money to shift to a new aircraft and it would take a large incentive for them to put their eggs in a new basket.
US is probably the most important market at present and operating there gives other airlines a lot of confidence to buy the jet. If you see the orders for MRJ, most are from US (In fact, almost all orders are from either US or Japan). The Superjet, in contrast, hasn't even applied for FAA certification as far as I know.
Promising and delivering lower costs are completely different things. Airlines are more prone to believe companies that have a proven track record of manufacturing civil aircraft than a newcomer.
The Superjet is the first airliner to be developed in Russia since the end of cold war. As such there are questions about its industrial capability and quality control processes. Mitsubishi, on the other hand is engaged in a number of aircraft projects (it makes more than a third of 787 structure).
Sukhoi has to build a supply chain and support system from scratch (Superjet has a number of foreign components). Again, in the extremely cost sensitive airline industry with tight schedules, there is a perception that the Russian aircraft will not be supported as well as their western counterparts (For example, Boeing boasts of a >99% dispatch reliability for 737)

Interesting question: I remember having read long time ago, that Russian-built airliners tended being underpowered respect to their western counterparts, this resulting in slow climbing and other operational difficulties for air-traffic controllers.

Also, the USSR airplanes' instruments were metric; besides pilots say that feet are a bit more accurate in estimating height for things as precission landings, one meter is around three feet, also a mile is a minute of arch, no match between a km and arches, some problems resulted, for example, in places where metric units were used for fuel. For those having a local way for measurement, it's easier adapting to using it plus another more universal system than the reverse, from the general to the private, habitudes are hard to change

A Mars probe crashed when somebody mismatched metric and 'imperial' units in the software, an airliner had to make an emergency landing in an abandoned airstrip, this won the pilot an award, as he managed the no engine, gliding approach at a too high level, by sliding on the side.
The reason of this commercial jet running out of fuel was a mismatch between fuel supply units.

They said also that USSR jet engines were more fuel thirsty than their counterparts, perhaps due to the lack of access to the rare elements used for high temperature and stress alloys, this limiting the efficiency of engines.


Would a helicopter with the blades on the bottom fly the same, if at all? I've heard that the pendulum rocket fallacy applies to rotorcraft as well. As stated above, I'm curious to know if a helicopter with blades on the bottom of the body would experience any effects from this. (Yes I know it's impractical and landing would be terribly difficult.)

Yes that is possible, like the Hiller flying platform demonstrated. It had two counter-rotating propellers inside a shroud and the pilot controlled his craft by shifting his body weight, like on a Segway. There is no law of physics that prohibits a helicopter from flying upside down.

The Hiller flying platform was one of several types built in the 1950s, after it was observed that controlling an underslung rotorcraft by weight shift could be learned by untrained personnel in 20 minutes. The DeLackner Aerocycle was another platform built based on this finding. The idea was later abandoned due to practical issues like kicking up rocks into the rotor blades, and an at the time unexplainable interference between the counter-rotating blades. The Aerocycle had a fixed rotor head, the dynamics of which were poorly understood at the time.

For full scale helicopters, having the rotor underneath the helicopter has the same stabilising effect on flight characteristics. Stability of helicopters (and of fixed wing aircraft) is studied from the perspective of aerodynamics: the effects of wind gusts or control inputs.

In the hover, the speed stability ${\delta M}/{\delta{\dot{x}}}$ plays a significant role: if positive, the hover is unstable. A human can learn how to control an unstable platform if the time period of the oscillation is high enough (conventional helicopter pilot), but it is much easier to fly in an aerodynamically stable aircraft (the underslung platforms intended for general infantry personnel). The speed stability effect in the hover equates to a gust of wind blowing from directly forward, does then the change in moment tend to amplify or counteract the effects of the gust. This can be visualised like so:

Image source

The gust blowing on the helicopter tilts the rotor back, which tilts the thrust vector. A teetering conventional rotor has a positive ${\delta M}/{\delta{\dot{x}}}$: it wants to flip backwards ever stronger, and is therefore aerodynamically unstable in the hover. An underslung teetering rotor has a moment change that stabilises: it tilts the fuselage back, and due to aerodynamic coupling the rotor follows back to neutral. A rotor with hinge offset has a smaller stabilising moment, but a stronger fuselage/rotor coupling.

So to answer your original questions: Yes the helicopter with an underslung rotor would fly, and it would be easier to control than a conventional helicopter. It is just a bit unpractical, that's all.

the issue that isnt being adressed by these "engineers" is stability. lower rotor/tall mass mass aircraft are heavily affected by small movements of the mass above the rotor, taller rotor/lower level mass aircraft dont have this issue due to the fact that changes in mass position do not affect the vector of the thrust to mass position in the same manner as it does when the payload is above the rotor. this was proven by the navy and the airforce with their "lifting platforms" that utilized thrust from below the  pilots. the other issue is the fact that these craft used liquid fueled internal combustion engines which also caused mass changes  due to fuel use, which destabilized mass distribution.    Electric model choppers and drones dont use liquid fuelwhich shifts as the craft shifts from upright to upside down.  In short there are multiple laws of physics that work against low rotor position air craft.


Can an ultralight aircraft fly with a 18hp engine? I have some questions - I'm planning on building single seat UL aircraft with this plan sketch (I have more), I drew this based on real plain and some research. Empty weight is between 50-70kg with engine

The power plant I will use this engine. 4 stroke, OHV, single cylinder, 440cc, power 18hp/3600 RPM, torque 3.0 kgm/2500 RPM (21.7 lb ft), ignition TCI, gross weight 37 Kg.

My questions:

Is this engine enough to make it fly?
Do I need belt reduction or gear reduction for a 1 meter propeller?
What propeller size to fit with this engine?
Do you see any problems with this design?

https://en.wikipedia.org/wiki/AmEagle_American_Eaglet

I found this on Wikipedia, it use a McCulloch MC101 15HP engine with 9000 RPM, that's make me doubt to use SFE 460 because the RPM far bellow. I can't find McCulloch MC101 here

It's possible to arrive at a rough estimate by assuming that the L/D ratio is 9. Now, the empty mass is 70 kg. Let's add 45 kg for the engine, transmission and propeller. And we must not forget the mass of the pilot (85 kg) and 20 kg of fuel. It's a total mass of 220 kg. Let's round it to 250 kg in order to be on the safe side.

If we imagine the plane gliding at L/D = 9 and 25 m/s, the sink speed will be 25/9 = 2,78 m/s. As the mass of the plane is 250 kg, its weight is 2450 N. Thus, the 'gravitational power' involved in the glide is 2,78 x 2450 = 6805 W.

The plane, for straight and level flight, will need exactly that power. If we assume that the transmission and propeller losses are 50%, you'd need twice that power, that is, 13,6 kW. Besides, some extra power is needed, (in order to climb, for example...) so let's increase the figure by 30%. 13,6 x 1,3 = 17,68 kW = 24 hp. That's the engine power that, in theory, and according to this simplified estimation, would be needed for that plane...

18 HP is more than good enough. Wright Brd's proves it. Your plane seems perfect. However, %35-40 of the propulsion will be lost as "fuselage drag", where your HP's are valuable .

If you can split the power into two, like that in the "Colombon Cri Cri". (You can do it with proper Gates belt drive), you can use lighter props (0,7m) and nacalle drag loss will be limited to %15.

Good luck.


Why there so many pitch control surfaces on the Piaggio P180 Avanti? Picture source.

I have seen that there is kind of sonic aircraft like B-1B Lancer that used elevator and canard or fins at the same time for pitch control. That quite understandable because it is fighter jet that required high precision control. There are another airplane that used canard but not elevator, like Tupelov Tu-144. But this Piaggio P180 Avanti is quite strange for me. It is equipped with elevator, canard, and also another additional device. I am not sure that propeller airplane needs what needed by the above B-1B Lancer.

Then my question are, what is that device (number 2 in the picture), what is that name, and what is that for? Are device number 2 and number 3 controllable?

Surface 1 is a  horizontal stabilizer with elevator, just the same as on any other aircraft with a T tail arrangement.

Surface 2 is called a rear strake or a tail fin. There is one on each side of the fuselage. They provide extra stability during operation at high angles of attack when the fuselage is disturbing the airflow to the vertical tail. They are not movable.

Surface 3 is a canard, providing extra lift. The canards on P.180 have a trailing edge flap. The flap is necessary to counteract the nose down trim of the flaps in the main wing. Without the canard flaps the elevator would not have sufficient authority to maintain adequate pitch control when full flaps are deployed on main wings.

Surfaces 1 and 3 have movable parts, but surface 1 is the only surface connected to pitch axis control of P.180.

Piaggio P.180 article on Flying magazine explaining design features (and a lot more).

Rear strakes- tail fins on Wikipedia

There is really some useful information in all answers. Two design choices really make me wonder how hard engineers worked to create that aircraft.

First; ventral strakes or tail fins. They are canted 45 degrees. Which means they  provide both pitch and directional stability. I also think they provide little bit of dihedral effect. Actually that maybe the main reason looking at straight mid-body wings and rectangular shape of engines. I’m sure they suffered from roll instability at the beginning. Canted ventral fins looks like a quick aerodynamic band-aid.

Second the front wings (as company calls them, not canards). It really wouldn’t make sense if they were really fixed small wings in front. They would make aircraft unstable in pitch. As the AOA increases lift of those front wings would increase also and aircraft would want to pitch up more and go out of control.

The truth is as @Jpe61 mentioned in his comment and as you can see at the beginning of that video they have trailing edge control surfaces. Looking at the location of wings and engines I think they suffered from aft CG problem and fixed that with the forward wings. I believe they produce downward lift though which provides stability at the expense of efficiency.

Lastly; I want to say that the more extra surfaces you see on an aircraft, thats the testament that basic aircraft has relatively more stability and control issues. Though that's not a bad thing on itself if its fixed properly.

Don't want to spark a discussion, but turns out that the most worshipped designs are the flawed ones. Don't believe me; look at P-51 Mustang or F-4 Phantom. :))


What happens during a powered descent? I was having a discussion with my friend about equilibrium condition in flight:

Scenario:
While going in straight and level flight, say I reduced my airspeed by 30 mph.
At the same time keeping the airplane's attitude strictly the same as before
(doing whatever it takes to keep the nose where it was before).

Reducing the speed means, the aircraft develops less lift: Aircraft is supported by less pounds of lift force (meaning which lift is less than weight)

What happens next? (imagining that pilot does not nose down)

My take:
1. Since weight > lift, aircraft drops attitude and falls like a stone that was dropped in midair unless the nose is down.

My friend says:
2.  The airplane finds new lift. This sinking motion creates lift
for aircraft. But it will not maintain straight level flight but descends. It will be a steady descent not accelerating descent. (not like a stone falling out of sky). He says this is called power descent

My question is:

1) Who is right here

2) If my friend is right, if aircraft can find lift after it descends (which means it found equilibrium) , why can not it maintain straight and level flight. And what exactly caused it to find new lift? Has angle of attack changed?

Neither of you are necessarily right, but you both have some understanding which is accurate.

Let me reiterate what you have stated, for clarity's sake. The scenario starts with the aircraft flying straight and level. Then the airspeed is reduced by 30 mph through a power reduction while the attitude is held constant. Regardless of what else happens we all recognize that this will result in some type of descent.

You are right in that the airplane has lost "lift" from the lost thrust and will thus descend. Depending on the aircraft and the starting airspeed, you might be right that the  aircraft might respond with an uncommanded attitude pitch down. If that were the case, it would be due to the scenario resulting in an aerodynamic stall. However, even if the aircraft were to stall it would not drop like a stone (that is, with no lift to oppose gravity), but would descend at what would still be a substantial rate of descent while still producing some lift to oppose gravity. Moreover, considering the possible entry speeds and attitudes, a stall would be unlikely in this scenario.

Your friend is right in that, with sufficient airspeed and no aerodynamic stall—both of which depend on the airspeed at which the maneuver was started—this scenario will result in a descent. It would be accurate to call this a powered descent. Depending on what he means by it, your friend may not be quite right to think that any "new" lift would be produced by the sinking motion itself, but this might be a difference of semantics. Let's explore this further.

Let's consider a Cessna 172 cruising straight and level at 110 mph. We then reduce the power to maintain 80 mph and hold the pitch attitude exactly where we started. In this scenario we have transitioned from cruise speed to something closer to the aircraft's best rate of climb speed. This means that we have transitioned from a high speed, high drag region of flight to a lower speed, lower drag region of flight. At the same time, by holding the aircraft's pitch attitude constant, we have changed from a low angle of attack, low coefficient of lift region of flight to a high angle of attack, high coefficient of lift region of flight. This increase in angle of attack is due to the new angle of the relative wind introduced by the aircraft's descent. The overall amount of lift doesn't change, but the way the lift is created does change. As the speed is reduced the wing's ability to create lift (expressed by the coefficient of lift) increases with the increase in angle of attack. Thus the lift doesn't change, but the lift is now due more to the angle of attack than the airspeed. If this is what your friend means by "new" lift introduced by the sinking motion, then he is right.

However, this "new" lift must be understood to be due to the angle of attack change, not an increase in net speed (kinetic energy). The lift isn't actually changing, merely the way in which it is created—angle of attack as opposed to speed. However, if the scenario were different and we allowed the aircraft to pitch down as we reduced power, the aircraft would pitch down to maintain about 110 mph, and the wing's coefficient of lift would change very little as the airspeed and angle of attack remained relatively constant.

I think you (and some of the answerers) are making this way more complicated than it needs to be. These are the facts:

(1) If you are in level flight and you reduce power, you will descend. This is the normal way to descend.

(2) If you are in level flight and you push the yoke forwards, you will go faster.

(3) If you are in level flight and you pull the yoke back, you will slow down.

That is all there is to it. Don't make it too complicated.


Why is lift larger than thrust? It's been a while since I tried to read a little about flight mechanics and aerodynamics, but I remember one question I had back then:

Is the thrust of a common passenger aircraft (A320, B737) greater than its lift-off weight and thus could it take off vertically?

A320:

Max take-off weight   73.5 (78) tonnes
Thrust range  98 (120) kN

73,5 tonnes = 73500 kg * 9.81 m/s^2 = 721035 N = 721 kN

If my calculations are correct, it could clearly not (a result like what one would expect intuitively)!

But how can the dynamic lift be larger than the weight using comparatively little thrust?
Rephrased: How can the dynamic lift be larger than the thrust?

Is there an invisible equivalent to gears at work here?

Thrust is needed to overcome drag, and a good airplane design can create a lot of lift for little drag. In the case of an A-320, the lift-to-drag ratio is 18 in cruise (a little less during take-off), so to lift those 78 tons needs only 4.33 tons of thrust. All it needs is the right amount of forward speed, and the engines only need to maintain this speed.

Gliders are even more efficient, their L/D can approach 60. A glider of maybe 450 kg mass (= 4412 N weight) will create a drag force of only 74 N, admittedly at a much slower speed than an A-320.

To be more precise, in a climb the thrust will actually compensate a little of the weight, in addition to the drag, depending on the climb angle. The thrust needs to grow by weight $\cdot$ sin($\gamma$), where $\gamma$ is the flight path angle. If the A-320 had enough thrust to lift all its weight, it could take off vertically, flying in a nose-up, vertical attitude. Modern fighter aircraft do really have that much thrust installed.

This drawing shows a climbing aircraft. There are four forces at work:

Lift L (blue arrow)
Drag D (red arrow)
Thrust T (green arrow), and
Weight m$\cdot$g (black arrow)

For a trimmed state, the concatenated arrows should form a closed trapezoid (lightly shaded arrows). Note that both thrust and drag are drawn longer here in relation to weight and lift than they are in reality.

To answer the why part needs a few more lines. Lift is created by deflecting the airstream over the wings downwards. This change in momentum is lift, and creating it would be free of drag if the wing's span would be infinite and the air inviscid. In reality, flying causes these drag components:

Lift creation incurs a small backwards-pointing component which is biggest at slow speed and decreases with speed. To be precise: This drag component is proportional to the aircraft's span loading (weight divided by wingspan) and the inverse square of airspeed. It is called induced drag because it could be successfully calculated first with the same equations that describe electric induction.
Flying through air causes friction. This friction drag grows almost with the square of airspeed and is proportional to air density and surface area.
In inviscid flow, the sum of pressures around a body would just cancel out. In reality, the pressure on the forward-facing sections is normally higher than that on the aft-facing sections. This drag component is called pressure drag and is also proportional to the square of airspeed at the same angle of attack.

At the speed of best L/D the sum of 2 and 3 is equal to 1, and 2 and 3 are of the same magnitude for a well-designed airplane. High subsonic and supersonic flight adds a fourth component, called wave drag, and it's onset is the reason why the A-320 prefers to fly not much faster than Mach 0.78.

Lift is greater than thrust because for a plane able to fly it can be demonstrated experimentally (in a wind tunnel) that Lift_constant > Drag_constant.

The formulas for lift and drag are:

1) Lift = Weight = Lift_constant x Density x Reference_surface x V^2

2) Drag = Thrust = Drag_constant x Density x Reference_surface x V^2

From 1 and 2 it follows that:

Lift = (Lift_constant / Drag_constant) x Thrust

If the plane is built in such a way that Lift_constant / Drag_constant > 1 then Lift > Thrust, otherwise it is not.


Are test pilots who work for the FAA paid on the GSE pay tables? Many employees of the US federal government are paid according to the GSE salary tables. Are the FAA test pilots paid on the same table? For example someone could be in the grade 14 step 6 rate. Or, are they paid according to some other pay table?

Yes, FAA test pilots are paid based on the General Schedule for the levels of GS-1 through GS-18.

If you are interested in reading the job description, one can be found on AvJobs.

The relevant section for pay is this one:

  Wages and Benefits

  Most Federal Civil Service employees in the aviation field are covered by the General Schedule and their salaries vary according to their grade level (GS-1 through GS-18). Within each of the grades provided in the General Schedule, provision is made for periodic pay increases based on an acceptable level of performance. With an acceptable level of competence, the waiting period of advancement to steps two, three and four is one year, steps five, six and seven is two years, steps eight, nine and ten is three years. The starting grade is normally GS-7. Trainees are paid while learning their jobs.

  The entry level is GS-9. Entrance salary will vary with the degree of the applicant's experience and training.

I'm not aware of the FAA having a corps of test pilots; that's usually the domain of the OEMs themselves who have their own private test pilots employed by them.  Military test pilots are paid at their officer rank grade level.  NASA also has test pilots who work for them, who are paid on the GS pay grades, generally a GS 12-13 job for starters.


Does a Second In Command have to be landing and instrument current like a Pilot In Command does? When flying an airplane that requires more than one crew member, does the SIC need to be landing current and instrument current, or is this a requirement only for the PIC?

Does it matter which regulations that you are operating under (Part 91, 121, or 135)?

FAA

This is a compilation of what I could find relevant to the question. Feel free to come up with corrections if I missed anything (I'm an EASA FCL guy)

Co-pilot Landing Currency:

Part 61: 3 takeoff/landings in previous 12 months (61.55)
Part 135: no requirements other than those in part 61 (above)
Part 121: 3 takeoff/landings in previous 90 days (121.439)

Co-pilot Instrument Currency:

Part 61: no requirements for SIC
Part 135: 135.245 requires that SIC's must meet part 61 PIC instrument currency requirements in 61.57(c) (see below)
Part 121: recurrent flight training every 12 months, including at least 1 ILS approach to minimums

Following is the list of relevant FARs :

§ 61.55 Second-in-command qualifications

  (b) Except as provided in paragraph (d) of this section, no person may serve as a second in
  command of an aircraft type certificated for more than one required
  pilot flight crewmember or in operations requiring a second in command
  unless that person has within the previous 12 calendar months:
  (2)
  Except as provided in paragraph (e) of this section, performed and
  logged pilot time in the type of aircraft or in a flight simulator
  that represents the type of aircraft for which second-in-command
  privileges are requested, which includes --
  (i) Three takeoffs and
  three landings to a full stop as the sole manipulator of the flight
  controls;

  (d) This section does not apply to a person who is:[...operating part
  121,125,135...]

  (e) The holder of a commercial or airline transport
  pilot certificate with the appropriate category and class rating is
  not required to meet the requirements of paragraph (b)(2) of this
  section, provided the pilot: [... is not carrying paying
  passengers...]

§ 61.57 Recent flight experience: Pilot in command.

  (a) General experience.

  (1) Except as provided in paragraph (e) of this section, no person may
  act as a pilot in command of an aircraft carrying passengers or of an
  aircraft certificated for more than one pilot flight crewmember unless
  that person has made at least three takeoffs and three landings within
  the preceding 90 days, [...]

  (c) Instrument experience.

  Except as provided in paragraph (e) of this section, no person may act
  as pilot in command under IFR or in weather conditions less than the
  minimums prescribed for VFR, unless within the preceding 6 calendar
  months, that person has: [...6 approaches, holdings, intercepting
  &tracking course...]

§ 135.245 Second in command qualifications

  (a) [...] no certificate holder may use any person, nor may any person
  serve, as second in command of an aircraft unless that person holds at
  least a commercial pilot certificate with appropriate category and
  class ratings and an instrument rating. For flight under IFR, that
  person must meet the recent instrument experience requirements of part
  61 of this chapter.

This is an excerpt from an FAA Legal Interpretation concerning 135.245:

  Next, unlike a PIC, an SIC's qualification to operate an aircraft
  under IFR in part 135 service is not dependent on compliance with §
  135.297.  Rather, § 135.245 sets the qualifications for pilots serving as SIC in part 135 operations.  It states that a pilot must meet the
  instrument experience requirements of part 61 to serve as SIC in
  flight under IFR.  Section 61.57(c) sets out the recent instrument
  flight experience requirements which include, among other things, six
  instrument approaches within the previous six months.  See Legal
  Interpretation to Gerald Naekel, from Donald P. Byrne, Assistant Chief
  Counsel Regulations and Enforcement Division (June 18, 1991) (noting
  that although the section title refers to pilots in command, the
  instrument recency requirements of that section apply to SICs).

§ 135.247 Pilot qualifications: Recent experience.

  (a) No certificate holder may use any person, nor may any person
  serve, as pilot in command of an aircraft carrying passengers unless,
  within the preceding 90 days, that person has—

  (1) Made three takeoffs and three landings as the sole manipulator of
  the flight controls in an aircraft of the same category and class and,
  if a type rating is required, of the same type in which that person is
  to serve; or [...]

§ Part 121.433 Training required

  (c)Recurrent training. (1) No certificate holder may use any person
  nor may any person serve as a required crewmember on an airplane
  unless, within the preceding 12 calendar months --  (i) For flight
  crewmembers, he has satisfactorily completed recurrent ground and
  flight training for that airplane and crewmember position and a flight
  check as applicable;

§ Part 121.439 Pilot qualifications: Recent experience.

  (a) No certificate holder may use any person nor may any person serve
  as a required pilot flight crewmember, unless within the preceding 90
  days, that person has made at least three takeoffs and landings in the
  type airplane in which that person is to serve.

EASA

FCL is very clear about it: PIC and co-pilot both need to be landing current. If holding an IR rating then specific night currency is not required. No instrument currency is required as long as the IR is valid.

FCL.060 Recent experience

  (b) Aeroplanes, helicopters, powered-lift, airships and sailplanes. A
  pilot shall not operate an aircraft in commercial air  transport or
  carrying passengers:

  (1) as PIC or co-pilot unless he/she has carried out, in the preceding
  90 days, at least 3 take-offs, approaches and  landings in an aircraft
  of the same type or class or an FFS representing that type or class.
  The 3 take-offs and landings shall be performed in either multi-pilot
  or single-pilot operations, depending on the privileges held by the
  pilot; and

  (2) as PIC at night unless he/she:

    (i) has carried out in the preceding 90 days at least 1 take-off,
    approach and landing at night as a pilot flying in an aircraft of the
    same type or class or an FFS representing that type or class; or

    (ii) holds an IR;

14 CFR 135.329 (e)(1) states that crew members are to be:

  ... adequately trained and currently proficient for each aircraft,
  crewmember position, and type of operation in which the crewmember
  serves

Which would indicate to me that the S.I.C. also needs a 135.293 ride in left seat which would also include an ILS to minimum as well as a non-precision approach.


Will ATC proactively route traffic around bad weather? When thunderstorms or other severe weather crop up, will the Air Traffic Control in the area proactively route traffic (horizontally or vertically) around the trouble area, or do they leave it up to the individual pilots to request an alternate route?

My intent was asking about commercial aircraft flying IFR, however the information about general aviation and VFR is appreciated

Yes, ATC will reroute flights that are operating on Instrument Flight Rules (IFR).
There are lots of videos of flights getting routed around severe weather floating around on the internet! Atlanta is a great example, as is Memphis, FedEx's hub.
In addition, NASA is working on a product called Dynamic Weather Routes that will help controllers be smarter about amending planned or unplanned weather reroutes.
Sort of, for aircraft operating VFR.
VFR flights that are talking to ATC may get advisories about weather and suggested headings from the controller. I've received notifications about things like 'moderate to heavy precipitation 5-10 miles ahead' many times when operating on VFR flight following.

Pilots do not "request routes" except when entering or exiting congested air space, or Class A air space or IFR conditions. They optionally notify ATC of where they might be going by filing a flight plan. VFR pilots can also request flight following. When flight following is activated ATC will notify you of other aircraft or weather conditions that could cross your path.

In uncontrolled airspace, ATC will notify you of a dangerous condition if you are on a flight plan that would bring you into contact with dangerous weather or have flight following activated. It is up to the pilot to decide what to do with that information. In controlled commercial airspace (Class A), ATC will actively route aircraft around dangerous weather conditions.


How are cruise missiles different from ballistic missiles? Cruise missiles and ballistic missiles are used by many nations as offensive and defensive technology. How do cruise missiles and ballistic missiles maneuver, and what are the differences between the basic principles of these maneuvers?

A cruise missile is rocket or jet powered and flies to its target within the atmosphere, using lift to stay up. Most have wings, although a few may use lifting body designs. They maneuver using control surfaces on the wings and tail like an airplane. Mission profiles can include big course changes, to evade air defenses, or to hug terrain to stay hidden. They can be launched from fixed ground positions but most are launched from mobile platforms. They tend to have shorter ranges than ballistic missiles.

A ballistic missile is a rocket that powers its way out of the atmosphere and coasts in an arc, re-entering the atmosphere before hitting its target. They have little maneuvering capability, once the boost phase is done it's all down to physics. Some warheads are able to maneuver a bit in re-entry in order to hit a pinpoint target, others are just rocks at that point. The largest ones are launched from fixed positions like missile silos but smaller ones are mobile.

Difference between cruise and ballistic missiles

There are some important differences between cruise and ballistic missiles. These are:

Ballistic missiles follow an arc-like trajectory and are launched
from the land or sea
They usually carry a nuclear warhead and are
very heavy
They rely on Earth’s gravity to fly down once launched
They have much larger range
Cruise missiles can also be launched from air and fly within Earth’s atmosphere
They have their own engines and wings to strike the target
They can be supersonic or sub-sonic and are highly accurate
They usually carry conventional warheads although some cruise missiles can also be equipped with nuclear warheads

In both cases, these missiles are guided. That is, the flight path is pre-determined and very small alterations in flight are possible, if at all.


Can a small plane be floated off of an aircraft carrier? Would it be possible to float a small plane (say a Cessna 150) off of the deck of an aircraft carrier without the Cessna achieving any forward motion with respect to the aircraft carrier? If not a Cessna 150, is there a standard GA aircraft that could do it?

EDIT:  Per a comment from ratchet freak: the takeoff would be done via lift from the wings, not via an engine duct (VTOL), like a Harrier.

As far as I'm aware this has never been attempted (and I doubt the Navy would let me try - though I'm certainly game if they are!), but:

A Piper J3 Cub stalls at 38mph (33kts).
The USS Enterprise (CVN-65) had a maximum speed of 38.7mph (33.6kts).

So, given a lightly loaded cub and an Enterprise-class carrier at flank speed, it is at least theoretically possible to float that aircraft off the deck (if it were lightly loaded, and thus had a lower stall speed).

Achieving zero relative motion would require a little more effort - specifically you'd have to seek out a headwind, and the Cub would have to be operating at an airspeed above stall, but still pretty close to it.
For example, if the Enterprise were making 30 knots and steaming into a 10 knot headwind the relative wind on deck would be 40 knots. That's enough to lift the Cub, but as soon as it was in the air it would need to pull itself along (via its engine) to maintain that speed. The Cub would have zero relative motion above the deck at an airspeed somewhere around 40 knots).

As a (slightly ridiculous) bonus: The Belite Superlite has a stall speed of 28 mph (25kts). It would be theoretically possible to fly such a plane like a kite from an aircraft carrier. Its advertised takeoff and landing distances (both ~500ft) are also such that it could operate from a carrier deck without need for the catapult to launch or arresting wire to stop.

I took off once at Wellington airport, NZ in a Gulfstream Cheetah in winds gusting to 55kt. When I opened the throttle it lifted off with no forward ground speed at all. All that is required is a vessel fast enough to provide a steady 45kt wind speed over the decks.

Some designs of fast ferries like the INCAT wavepiercing catamarans would be ideally suited as some form of aircraft carriers like this.