Adding moisture creating fog? It may be a simple question and I've read the PHAK and searched online, but I can't seem to understand why adding moisture to a dry cold air mass would create fog. I understand when an air parcel is cooled to the dewpoint neared the surface, it will become saturated and fog appears. However, why would adding moisture create fog?

You can either cool the air to reduce it's capacity to hold water, or you can add water to the air. Either way will eventually make the air saturated

You can either make the bucket smaller, or you can add water in the bucket. Either  way you will eventually make the bucket spill ...


Can a pulse jet be used on a light GA aircraft? I have an idea for designing a light, cheap and fast 2-seated private airplane... I was thinking about using a pulse jet engine which is simple to design and build, and is cheap too.

Noise is not an important concern in my region. The only things that I'm wondering about are efficiency, fuel consumption (range), vibrations and cooling.

Is it feasible to use pulse jet instead of regular engines?
Is the pulse jet functional and operational?

In principle yes. But some details will turn most potential operators off.

Noise is the obvious first one. You might not mind, but cockpit noise and vibration in operation will certainly put an unacceptable stress on the pilot. Just think how you will communicate with ATC or with a co-pilot. Also, your choice of airports to operate from will be rather restricted.

Vibration also means that you need to ruggedise the airframe. This will certainly eat up some of the mass benefits of the pulse jet, but is hard to quantify.

Now fuel consumption: The AS-014 would consume 350 g of fuel per hour for every Newton of thrust. Compare this to the 60 g/Nh of a modern turbofan. The additional fuel will eat up the remaining mass advantage once you desire to fly for more than just a few minutes.

Next will be take-off distance. Unless you use a catapult, you will need a long runway. The pulse jet has limited static thrust, so your initial acceleration will be poor. At the high end of the speed envelope, though, thrust should be plentiful.

Cooling, however, is no problem. Just expose the pulse jet to the elements and you are all set.

To summarise: Yes, a pulsejet is a possible power source for a GA airplane, but is a poor choice for a multitude of reasons. It makes more sense in an unmanned, one-way application.


Is lowering V1/VR (and runway length required) the only reason for flaps at take off? I've read that some aircraft (examples include the Saab 340 and the Fokker 100) can perform flapless take offs, provided there is enough runway available. It's also my understanding that, in terms of lifting off the ground, any aircraft would be theoretically capable of that, as long as there were a long enough runway (which isn't the case in practice).

However, I was wondering why aircraft such as the ATR-42/72 or the Dash-8 still lower their flaps for take off, even from runways that are over 3000m/10000ft long. At least those I've flown with always did that.

Is there some other reason for non-flapless take offs, even with very long runways, for some models? For instance, anything related to pitch/roll stability?

For an aircraft designed for cruising efficiency it is important to have as little trim drag as possible.

See ATR 72 link:

The wing may appear unusually small, but it is made to produce the needed lift at cruising speed at its most efficient Angle of Attack, where lift to drag ratio is highest.  If the wing produced too much lift for level flight at its cruising speed, it would have to be "trimmed" to a lower AOA, at the expense of greater drag, there for a greater rate of fuel consumption.

The contribution of velocity to lift is described in the lift equation:

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

with $L$ being the lift, $C_L$ the lift coefficient, $\rho$ the density of air, A the wing area, and $V$ the aircraft velocity.

The ATR 72 cruises at 280 knots.  In order to generate adequate lift at lower velocities it either has to dangerously increase its AOA, or increase its coefficient of lift by adding camber.

Lowering flaps add camber, which is why this plane does it, as part of its take-off procedure.
Higher flap settings are generally avoided because they produce too much drag.


How to find waypoint IDs? Is there a website to find waypoint ID's from coordinate values?

I am looking for waypoints in the Indian ocean area.

One possible source is Skyvector

You can use it like a paper map using the Latitude and Longitude markings to find waypoints (or other positions).

E.g. What waypoints and routes are near S30°0.00' E112°00.00'

Hints: Click "World Hi", use your mouse's scroll-wheel to zoom, play with "Layers".

There are also sites with lists, by region, of waypoints with coordinates. One example is fallingrain


Can thrust reversers alone steer and stop an airliner? Is it possible to use ONLY thrust reversers to steer and bring a smaller size commercial jet aircraft, with a minimum amount of fuel onboard, to a complete stop, after touching down on a longer than average length commercial airport runway?

Steer: No. Stop: Yes.

Thrust reversers are either in or out. They cannot be engaged proportionally to some control setting in the cockpit. Once they are unlocked, the airflow through them sucks them out completely. The only way to vary their braking effect would be to throttle the engine up or down, and airliner engines react rather sluggishly to control inputs. Their responsiveness will not suffice to steer the aircraft; only rudder inputs (and those only at higher speed), nose wheel steering and differential braking with the wheel brakes are suitable for directional control on the ground.

Their braking effect is biggest at high speed and tapers off as the aircraft decelerates. For the first third of the landing run they will help noticeably in slowing the aircraft, but you will need a long runway when you want to land without wheel brakes. Details depend on landing weight, airfield elevation and wind speed.


How do I decode FAA SNOWTAMs? New FAA Notam site marks certain notams as Snowtam and provides Runway Condition. I can decode E) part using FAA Runway Condition. But how can I decode the Q section. Is there a comprehensive source for decoding Notams?

FAA publishes same notam in 2 different formats. I am interested in decoding ICAO Format.

ICAO FORMAT:

12/057 NOTAMN  Q) ZBW/QMRXX/IV/NBO/A/000/999/4221N07100W005
  A) KBOS  B) 1912310152  C) 2001010152
  E) 09 FICON 5/5/5 100 PCT WET  OBS AT 1912310152.

DOMESTIC FORMAT:

!BOS 12/057 BOS RWY 09 FICON 5/5/5 100 PCT WET OBS AT 1912310152. 1912310152-2001010152

So, a SNOWTAM actually has a different format, and your example is just a standard NOTAM in ICAO format.

12/057 NOTAMN  Q) ZBW/QMRXX/IV/NBO/A/000/999/4221N07100W005
  A) KBOS  B) 1912310152  C) 2001010152
  E) 09 FICON 5/5/5 100 PCT WET OBS AT 1912310152.

This decodes into the following:

Series and number:        12/057
Nature of the NOTAM:      New (N in the NOTAMN)

Q) Qualifier line:
   FIR:                   Boston FIR (ZBW)
   NOTAM Code:            Starts with Q and the following four letters:
                          Subject: Runway (MR)
                          Condition: Not Specified / Plain Language (XX)
   Traffic:               NOTAM issued for IFR (I) flights and VFR flights (V)
   Purpose:               NOTAM selected for immediate attention of flight crew members (N),
                          for PIB entry (B), and concerning flight operations (O)
   Scope:                 Aerodrome (A)
   Limits:                FL 000 to FL 999 (000/999)
   Geographical location: 42°21' N 071° 100' W (4221N07100W)
                          Operation radius of the NOTAM: 5 NM (005)

A) Aerodrome:             Boston Logan (KBOS)
B) From:                  01:52 UTC 31 December 2019 (191231 0152)
C) Until:                 01:52 UTC 01 January 2020 (200101 0152)
E) Text of the NOTAM:     Runway 09 Field Condition
                          Braking action 5/5/5 (good for each third of the runway),
                          Runway is 100% wet
                          Observed at 0152 UTC on 31 December 2019

We could dig into the ICAO documents to find the official guidance, but different countries implement it differently sometimes anyway.  Here's a good document that I found which breaks down the different codes.


Are there limitations in US legislation on a US citizen to own a MiG-15 in Europe? If US citizen buys cold war era MiG-15 jet fighter aircraft, which:
- had been acquired from the museum (facility of the Ministry of Defense one of the European Union countries, member of NATO) by private person (contract document is available);
- is still located in that country;
- at least for time being the plane will stay located in that country even after the US citizen buys it from that private person;

Now, since that US citizen is also dual citizen of that country:
- Is there anything which he needs to do to be in compliance with US law?
- Is there anything which he should not do to be in compliance with US law?
- Or, since the plane will stay in that country (no import/export will take place), is everything basically governed by that country law only and he is good just to stay in compliance with the law of that country?

Does the same apply to any weapon/armament accessories present like cannons, gun camera, gun sight, ejection seat? E.g. cannons are now independently stored at the third party, licensed to handle military material. He would not get cannons to his possession until unless they are modified (deactivated) according to the law of that country.

With mere possession the only issue you might run into is any live, functional weapons on the aircraft. This is governed more by the nature of the device than the person owning it. Generally speaking, Europe is far less accommodating regarding private citizen ownership of military weapons than the US, especially nasty ones like automatic cannons. If they have been demilled to the specifications of the country in which they reside, then they're not guns any more, just decorations.

A couple of years ago, I saw a Soviet era MI-24 attack helicopter for sale in the US. Main and tail rotors present, no engines, no weapons, cockpit was pretty much gutted, airframe was past its useful life, for static display only. It looked intact from the outside... and also looked very sinister. For some odd reason, my wife balked at me spending $8k on this ultimate lawn decoration. But, there were no regulations regarding its ownership, other than maybe a neighborhood association getting huffy about someone parking an attack helicopter in their front yard.

Now, if you want to actually fly the MIG15, that's a different matter. But if you as a US citizen want to purchase a MIG15 as a static display, without functional weapons, the only thing the US government is going to care about is whether you paid their income tax on the money you use to buy it.


Is there any advantage to having both wings integrated into a single wing unit, rather than being attached separately to the fuselage? if I have a wing, which is split in the middle of it and attached at each side of the aircraft (like in any commercial aircraft today), I get a bending moment at the root of the wing.
What if I have an continuous wing (box) like an oblique wing on the top of the fuselage? A friend of mine says, that this way the wing itself would carry its bending moments. How can I imagine this? Is this just like a beam? Does anybody has some papers about this?

The bending moment is produced by the lift generated by the wings and the weight of the fuselage in the middle, or on the ground the weight of the wings and the support (gear) mounted on the fuselage or fairly close to it. So it is always there.
The only choice you have is how to build the structure to carry that load. You can:

Have a central spar, a solid beam that carries the load, and unstressed or lightly stressed skin. That's how all the early planes with fabric-covered wings and fuselage were built.
Have a hollow wing with stressed skin supported by mesh of ribs and longerons. That's how most aircraft are made today. You have tension load on the bottom and compression load on the top and the centre is not doing much, so not having it there makes a lighter structure.
Anything in between, with solid spar, but some load carried by the skin.

Independently of that, you can

Build the structure in one piece and and attach the fuselage to it (from above, below or build it around).
Build the structure in several pieces and join them with rivets, bolts or glue.

In either case the structure is continuous through the fuselage. The fuselage walls would have no chance of handling the load if you didn't have any connecting structure inside and would bend easily. The only difference is whether it is joined from multiple pieces or not.


Requirements for Steady Level flight at various speeds Let an aircraft in a steady level flight be trimmed at certain speed. A level and steady flight at a higher speed can be achieved by changing throttle and elevator together ( and not just by changing elevator or throttle alone). How?

From a purely practical standpoint, let's say you're in a Cessna 172 (a common light aircraft often used for training) and you're in economy cruise at 2400 rpm at 6,000 feet on a standard day. According to the cruise performance chart I have here, you would be using 60% power, burning 6.8 gph, and have a true airspeed of 109 kts. You're hand flying the airplane as it has no autopilot.

Now the cute gal that you've talked into taking this trip with you mentions that she's beginning to need a bathroom. You neglected to bring along a urinal (and maybe more than a urinal is needed), so you decide to speed up to the maximum cruise speed for 6,000 feet. You consult the cruise performance chart and see that you can get 75% power at 2600 rpm. That will increase your cruise speed to 120 kts at the cost of burning 8.4 gph.

You would smoothly increase the rpm to 2600. As the power came up, you would have to hold a little forward pressure on the elevator to keep from climbing. If you're used to the airplane, you might unconsciously reach down to the trim wheel and roll in a little down elevator. In any event, you will eventually want to trim out the down elevator force you're holding on the control wheel.

If you set 2600 rpm to start the speed up, you'll notice that the rpm goes a little above 2600 as your speed increases (this is a fixed pitch propeller), so you monitor and adjust the rpm as necessary to settle on 2600 rpm with elevator forces trimmed.

If you have an autopilot with an altitude hold function but that doesn't control the power, all you'll have to do is control the power.

If you have an autopilot with FADEC, just set what you want and it will do all the work from there.


In an unpressurized cabin, why is the cockpit ambient pressure lower than the outside pressure? As I study for my IRA written, this (VFR) question resurfaced and continues to irk me. The annotations cite the Venturi effect as the sole reason, but I don't follow.

From Wikipedia: "The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section (or choke) of a pipe"

Do we consider the parcel of air in the cabin to be the fluid moving through the constricted section of some imaginary/abstract pipe? If so, why? Can anyone shed more intuition on this?

The air moves around the fuselage, which causes a localized increase in velocity around the aircraft.  This increase in velocity causes a slight decrease in the outside air pressure, which effectively sucks air out of the fuselage, making the cabin at a slightly higher pressure altitude.

The effect is localized.

While the reduction in pressure, and increase in pressure altitude inside the cabin is small, many GA aircraft display a 40 foot or so difference in pressure altitude between the alternate static port (inside the aircraft) and the pressure altitude with the factory static port.


What are the differences between these types of air cycle machines? I am MSC student of mechanical engineering and my project is about ACM machine. I have read something about various systems of air conditioning system in aircrafts;

simple system
boot strap
reduced ambient temperature
regenerative system
boot strap with evaporator
simple system with evaporator

I just know that reduced ambient temperature is for supersonic aircraft.I don't know other systems applications.For example, when is a regenerative system used and when boot strap is used?

Are all of the possible air conditioning systems exists in every aircraft and switch to another depending on flight condition?

Really not sure what you're asking, nor do I know what these terms you've found mean, so let's start with these drawings and see where we end up.

DC-9 Bleed air enters from the engine (or APU) at bottom left of this drawing and enters the primary heat exchanger. Then it enters the compressor in the ACM and then on to the secondary heat exchanger. From here it enters the turbine and this is the point that the heat loss occurs and cold air enters the water separator and then the cabin of the airplane.

Note the anti-ice screen and the pack anti-ice valve which adds a little heat if the air exiting the turbine is too cold and is causing ice.

The water separator is a cone-shaped cage with a heavy cotton bag over it. This collects condensation in the air and dumps it on to the face of the secondary heat exchanger to cool and improve it's efficiency.

Temperature in the cabin is controlled by the temperature control valve on the left side of the drawing.

737 This system is very similar to the DC-9 and really the main difference is that the pack anti-ice valve here is operated electrically, while on the DC-9 it is done mechanically with a pneumatically operated valve.

757/767 This is a much different system, many more electrical sensors and control. The pack cooling fan is an integral part of the ACM, where on the other two systems they are separate components. The water separators are much more advanced and don't require regular maintenance like on the other systems.

As you can see, these three systems are all basically the same with the only real difference being how they are controlled and some of the ancillary components.


How widely accepted and used is the International Standard Atmosphere? Is it used in the US as well for an example, where there is the US Standard Atmosphere. With different standard models, how widely is the International Standard Atmosphere applicable? Or is it only used in Europe, and some countries outside of it?

Appreciate your feedback.

In most aviation contexts, the International Standard Atmosphere is used universally. This includes things like developing aircraft performance charts, weather forecasts, and flight planning. All flying rules and other aviation standards are all based on ISA.

There are several atmospheric standards. However, for the most part, all of these standards are the same up to about 32km altitude. Since most airliner traffic occurs between about 10km and 20km, there is no need to reference different standards in different locales.

The International Standards Organization (ISO) publishes the atmospheric standard as ISO 2533:1975.  Sometimes this is referred to as the ISO Standard Atmosphere, which would have the same ISA initialization.  However, when used in textbooks, performance charts, flight planning, etc., the term ISA is always understood to mean "International Standard Atmosphere". For the rest of this answer, assume ISA to mean International Standard Atmosphere.

ISA is also an initialization of one of the other standards: ICAO Standard Atmosphere, published by the ICAO in Document 7488/3. The ICAO standard was first published following the 1950 ICAO Council, and underwent multiple changes over the years. in 1979, the Council approved the re-calculation of the data tables to align with the ISO standard of 1975. Once this was complete, the ICAO Standard Atmosphere and the ISA were identical. The ICAO document states that, "any future revisions of the ICAO Standard Atmosphere will be subject of the coordination of the two bodies [ICAO and ISO]".

Because these two standards are the same, AND also have the same initialization of ISA, AND aviation standards world-wide are driven by ICAO, there are frequent mis-uses of the term ISA within the aviation world as being the ICAO standard. However, when used in the application of aviation "things", like calculating True Air Speed, knowing whether the temperature at an altitude is + or - from ISA; it is the International Standard Atmosphere that is meant by ISA.


How the maximum service interval is related to UAVs? I´ve been reading about the aircraft´s maximum service interval but this concepts is hardly related to the day to day aircraft (civil and military ones of course). How does this concept is related to UAVs?

Note: I´ve restructured the question, I´m sorry for the previous one

Service interval  - is a maintenance term indicating the interval (either in time or number of flight cycles) between two successive services (e.g. inspection, change of oil, etc.) that a component requires.

In case of UAVs this is not different. It can be for example that the Service Interval of the engine is 100 hours of flight time, meaning that the UAV can fly missions for 100 Hours between engine maintenaince services.


Are pilots generally trained for crosswind landings? A YouTube footage of a KLM Boeing 777 landing at Schiphol airport in the Netherlands is certainly scary as the plane bumps and weaves and rolls from side to side.

Are pilots generally trained to handle such eventualities (or are such landings common in certain regions of the world?) or was everyone involved including the pilot taking a risk in this case without diverting the aircraft to a nearby safe location?

Of course yes.

Crosswind landings, like the one in the video you linked, are very common. In fact, landings with no wind or only headwind are rare.

There are several techniques pilots are taught during their extensive training to land aircraft when there is crosswind. The Wikipedia article I referenced above lists them. Since your question isn't about them, we won't discuss them.

Certainly, extreme weather situation are not very common. Some parts of the world experience extreme weather more than other areas. Diverting to other airports is not always an option and in some cases, once an airplane is on the approach, going around becomes impossible.


Can flight control computers detect and help to avoid pilot-induced oscillations? With flight control technology available today like fly-by-wire, digitally augmented command inputs etc., I wonder whether any technical solution exists (or could possibly exist) to detect and counter the occurrence and dangers of pilot-induced oscillations (PIO).

Consider for example a low visibility final approach scenario:

Is it possible to detect an early onset of PIO and either augment pilot input to prevent further amplification of oscillations, or, less intrusive, give some (e.g. aural) warning to the pilot?
Also, a fully developed PIO situation might be detected and a warning triggered to increase awareness or prompt the pilots towards an eventual go around, similar to windshear warnings.

If feasible, do such technical mechanisms exist, or would they even be considered helpful by pilots at all? I imagine a critical part to solve would be not to override an actually intended control input by the pilot (that is within the usual safe envelope).

PIOs occur because the pilot senses a rapid movement and feels the urge to counter it. Key is the frequency of a few Hertz, so the pilot's reaction kicks in with a phase shift such that it promotes the movement, and low damping such that the oscillation amplitude grows over time. With a working FCS this kind of rapid movement should not happen.

However, once the FCS is not tuned to the situation, it can actually aggravate the situation and promote PIOs. The best known case is probably the 1992 crash landing of Tom Morgenfeld with the YF-22 prototype.

Here the gains in the FCS were set too high with afterburner on and gear up at slow speed.

Another case happened in the early phases of flight testing the V-22 Osprey. Here two of the three gyros in the control system were incorrectly wired and the pilot made a wrong control input.

So it is less the ability of the FCS to detect PIOs than its improved damping which never lets a rapid oscillation happen in the first place.


What's the Canadian equivalent of a Biennial Flight Review? Is there an equivalent? Googling I didn't learn much.

There is a requirement to complete a flight review every two years. I guess it's technically just a 'FR' but for all intents and purposes it is a BFR!


Is ATC connected to the Internet & why? I've just read an article from SkyNews just here where they said it's expected that one day air traffic control will be the target of cyber attacks.

So my question is "Is ATC connected to the Internet and why ?"

Are they just connected (if they are) to exchange information between the various ATC Centers and in this case I think they use VPN connections with military grade encryption or do they use Internet for other reasons ?

The Air Traffic Control system does transmit information over the internet. The Air Traffic Control system has a number of components, some of which transmit information over the internet. According to Review of Web Applications Security and Intrusion Detection in Air Traffic Control Systems, Office of Inspector General, DoT,

  ..Federal Aviation Administration (FAA) has increasingly turned
  toward the use of commercial software and Internet Protocol (IP) -based
  technologies to modernize ATC systems.

Note that the ATC is not connected directly to the internet. It is the behind scene connections, that are routed through the internet. According to a security professional,

  ... when most managers say there is no connection to the Internet, they are unaware of maintenance connections. Behind the scenes there are almost always semi-direct connections through routers shared between the control system and business systems that can be exploited

Actually, the use of internet for sharing of information is increasing. FAA's NextGEN modernization involves a significant amount of information transmission over the internet. According to US Government Accountability Office,

  NextGen is a modernization effort begun in 2004 by FAA to transform the
  nation’s ground-based ATC system into a system that uses satellite-
  based navigation and other advanced technology. ... These
  new technologies will use an Internet Protocol (IP) based network to
  communicate.

Image from GAO report on Air Traffic Control

This increasing connection to the internet does increase the associated risks. From the same GAO report:

  ... the shift to NextGen technologies will require FAA to replace its proprietary, relatively isolated ATC computer systems with information systems that interoperate and share data throughout FAA’s operations and those of its aviation partners. ... These new systems...will also employ digital and Internet-based computer-networking technologies, exposing the air traffic control (ATC) system to new cybersecurity risks.

As to why the ATC is connected to the internet, it basically boils down to ease of operation. According to [NATS], which manages UK airspace,

  We ... are now working all over the world within an industry where systems are connected across organisations, countries and continents.

Such an interconnected worldwide system requires a standard platform, which will not be possible (or atleast very difficult to maintain) if a closed, proprietary platform is used.

So, the ATC does use internet, though this is mainly to transmit information. However, I'm not aware of the security systems, though we can be sure that they do have some sort of encryption (If I'm correct, Lockheed Martin supplies the software) and have firewalls to protect the systems.


How to read the propeller range chart for DHC-6 Twin Otter? I understand constant speed propellers and beta range. However, I'm not completely sure I'm extracting everything from this chart that appears in a manual for a flight sim model of the Twin Otter.

Is this format common for describing propeller range in aviation?
Can someone describe the information exposed by the chart in words?

Source - Aerosoft manual

Most of high performance propeller aircraft use constant speed propellers, with variable pitch. The speed remains constant over (most of) the flight regime, while the propeller pitch is varied according to the requirement (by the Constant speed unit or CSU).
In case the propeller is stopped in flight (for example, due to engine failure), the propeller pitch is increased so that the propeller is basically parallel to the airflow, so as to minimise the drag. This marks the extreme value of feather angle 87$^{\circ}$ shown in the image.

Image from 12charlie.com
The propeller range used for forward  flight is usually called the $\alpha$ range, where the blade pitch has moderate values with constant speed, which is set by the propeller lever. Obviously, this speed is not constant over the entire range between engine start and shutdown. Usually around the idle, the rpm drops (this varies according to the design) and this gives the constant speed range limit.
Now, during landing, the aircraft speed is reduced usually using brakes etc. However, it is possible to do so using propeller itself- basically by turning it backwards. The $\beta$ range refers to the region where the propeller is producing zero or negative thrust.
From this article:

On PT6 powered aircrafts, the Bêta range is controlled by the PCL ( Power Control Lever ) which also directly control blade angle. Yeah, the governor is overriden and by moving the PCL past the idle gate ( you usually have to lift the PCL against that gate ) you directly schedule blade angle in correlation with Ng ( Gaz generator ) speed.

In the beta range, the aircraft can be slowed down by making the propeller pitch flat (0$^{\circ} 30'$ here) and creating drag. The reverse thrust starts after this, with the full reverse trust coming in at the limit -15$^{\circ}$.
I think there is some typo in the figure. From this answer(cleaned up):

Beta range in the Twin Otter is from 11° to -15°(reverse) propeller blade angle.
The Beta range lights will be lit when Your in the range from 9°to -15° propeller blade angle.


Is there a wake turbulence difference between B737s? I've heard pilots talking about how the new 737s produce much more wake turbulence then the model historically. They described it as similar to the 757, based on anecdotal experience. Have there been any studies of this, or is there a quantifiable difference between 737 models?

According to the Wake Turbulence Re-categorisation, the older 737's are Lower Medium, while the 737NG is Upper Medium.

High lift (weight) and low approach speed increase the wake turbulence. The newer 737's are heavier, while their approach speeds are not much faster than the older models.

The 757's are Lower Heavy. See: What is the cause of unusually strong wake turbulence from the 757?


What are the hurdles to overcome before purely electric commercial aircraft can fly? What are currently the largest issues with purely electric commercial aircraft (large scale ones like the size of a Boeing 737)?

Are there any organizations right now that are trying to solve those issues?

The biggest problem with an all-electric-powered aircraft is the same as those plaguing all-electric cars; our current battery technology has nothing on the energy density of fossil fuels:

There's just no contest in being able to pack the energy needed to push a plane through the air into a volume and weight compatible with an airliner. Jet fuel is kerosene, which is pretty much right in between gasoline and diesel, while any battery technology we've developed can't even be accurately plotted on the scale of this graph.


Should ADS-B airborne and surface squitter transponder registers both be updated regards air/ground status? ADS-B have two position squitters, airborne and surface. As far as i know, airborne position is broadcasted on air and surface position broadcasted on ground.

There is a "Squitter Capability Subfield" in BDS Register 10, which needs to be set if both airborne and surface position registers are updated within last 10 seconds. This kinda implies both registers shall be updated all the times.

Is providing data for both squitters necessary regardless of aircraft's vertical status? Can we select one of these squitters and provide data only for it?

I don't have the 1090ES MOPS at hand here, but it makes sense to me that both should be updated.

At the moment that the registers are updated, it is not necessarily clear whether an airborne or a surface squitter will be transmitted next. In the period between update of the register and transmission of its contents, the vertical status of the aircraft can change.


Did any aircraft ever use stick twist for rudder control? Did any aircraft ever use stick twist for rudder control like some joysticks for video game flight simulators?

Yes, the RAH-66 Comanche FBW system used a twist control for the yaw channel.
The RAH-66 Comanche used a twist in the pilot's stick to control the rudder/yaw inputs.  It had no rudder pedals.  (Yes, a helicopter is an aircraft).
Comanche unfortunately was canceled near the end of LRIP (Low Rate Initial Production) in 2004 as the program was moving into EMD (Engineering and Manufacturing Development). There were at least 2 prototypes flying at the time. Test and development flights took place from 1996 to 2004.
Extracts:

"... the RAH-66 Comanche design incorporated a 3-axis, limited displacement, uniquetrim sidearm controller [replacing cyclic and yaw pedals] for control of the longitudinal, lateral, and yaw axes. A proportional collective with approximately 6 inches of displacement was used. An enhancement tailored to the scout mission was the incorporation of limited control in the vertical (fourth) axis of the sidearm controller. This allowed the pilot to command stabilized climbs and descents with the altitude hold system engaged. This was used primarily for vertical unmask and remask maneuvers, which enabled the pilot to fly through the autopilot without even temporary disengagement."
— "Impossible To Resist" - The Development Of Rotorcraft Fly-By-Wire Technology (PDF—Paywall)

and

"The RAH-66 Comanche program has proposed 4-axis controller (Harvey, 1992), but this approach is now questionable."
— A Four-Axis Hand Controller For Helicopter Flight Control

(Source)

Note that either the '3 + 1' or '4 + 1' controller configuration would likely have been the ones decided on for the Comanche, on the basis that all the cockpit pictures that have been seen feature a sidestick and a collective stick, but no pedals.

As noted in the first text block (Impossible to Resist) the 3+1 (collective) was the final form, although the cyclic had some control authority in the vertical axis (as described). I added the emphasis in bold, and the note on "side arm controller" vs "cyclic" in brackets.


Could a modified J58 jet engine be used commercially? Could this mean for more fuel efficient supersonic commercial cruising?

If so in what ways would it need to be modified and how possible is this?

According to Wikipedia the J58 is comparable to the Rolls-Royce/Snecma Olympus 593 that powered the Concorde, so yes it's possible.

Will it be efficient? The Olympus 593 was as efficient as can be, even by today's standards:

  The Concorde cruised at Mach 2.05 with its engines giving a SFC of 1.195 lb/(lbf·h); this is equivalent to a SFC of 0.51 lb/(lbf·h) for an aircraft flying at Mach 0.85, which would be better than even modern engines; the Olympus 593 was the world's most efficient jet engine. However, Concorde ultimately has a heavier airframe and, due to being supersonic, is less aerodynamically efficient, i.e., the lift to drag ratio is far lower. In general the total fuel burn of a complete aircraft is of far more importance to the customer.

It's not just the engine that makes an aircraft efficient, as the paragraph above highlights. The amount of fuel the Concorde burnt for 100 passengers is the same for 700 passengers on two Jumbo Jets.

As I highlighted here, even if fuel is cheap, or the ticket price covers the fuel cost, propulsive efficiency isn't the whole story. The Concorde wasn't retired because of fuel. I'm mentioning the Concorde because of its very efficient engines and supersonic regime.


Can computer imposed inputs be overridden on the Boeing 737-MAX? During Lion Air Flight 610, a Boeing 737-MAX, it seems that the angle of attack sensors caused the software to believe the aircraft was stalling, thus initiating a nose-down pitch to recover from the (non-existent) stall.

I was under the impression that the difference between Airbus' fly-by-wire system and the Boeing types, is that Boeing aircraft can have their computer imposed inputs overridden (as discussed in my previous question).

So in the case of this flight, would pulling up have not recovered the flight, and if so, why not?

The new 737 MAX has a more advanced pitch control system called maneuvering characteristics augmentation system (MCAS), which automatically adjusts the stabilator trim in case of high thrust and high angle of attack (AOA). This makes it very hard to overcome the down force with elevator input alone (pulling up).

In case of a wrong trim adjustment (e.g. due to an erroneous AOA sensor), the pilots have to adjust the trim manually and maybe even turn off the stab trim via the cutout switches in the center pedestal (shown below). This was apparently not conveyed properly in the MAX differences training and the FAA has since issued an Emergency Airworthiness Directive.

737 NG:

(image source: flaps2approach.com)

737 MAX:

(image source: feitoffake.wordpress.com)

So compared to an Airbus, the Boeing pilots can still have all manual control, but they have to use manual pitch trim.


On an aerofoil or circular cylinder why does the airflow stay attached after passing the point of maximum thickness? Why does it follow the curvature rather than separating?
Its not due to the coanda effect as the accelerated flow near the surface of the aerofoil can't be considered a jet. It's not due to surface tension because there is no interface between two fluids. I know the flow of a fluid is due to pressure, inertial and viscous effects.

Is it due to viscous effects on fluid particles in the boundary layer?
Is is due to the pressure normal to the surface of any body submerged in a fluid?
Another reason?

Thanks for your answers!

This is due to the Coandă effect.
https://www.britannica.com/technology/fluidics#ref129652

In the 1930s Henri Coandă, a Romanian scientist, described what is now
known as the Coandă effect, a major contribution to fluidic
technology. He observed that as a free jet emerges from a jet nozzle
the stream will tend to follow a nearby curved or inclined surface. It
also “attaches” itself to and flows along this surface if the
curvature or angle of inclination is not too sharp. Coandă explained
this tendency as being caused by the jet stream’s entraining (picking
up) nearby fluid molecules. When the supply of these molecules is
limited by an adjacent surface, a partial vacuum develops between the
jet and the surface. If the pressure on the other side of the jet
remains constant, the partial vacuum, which is a lower pressure
region, will force the jet to bend and attach itself to the wall.


Can I check my density altitude with brake tension? The same way one would apply the brake and accelerator, the more torque the more break is needed to hold the car, can a plane use this same technique to check the plane thrust and air density before take off?
Using a brake pressure gauge, could density altitude be measured by how much pressure is needed to hold the plane in place?

You may be able to get a rough estimate of if your engine is producing sufficient thrust utilizing brake pressure. But, how will you determine how much thrust is being produced? Your brakes are not calibrated so carefully as to adequately determine that. You would only be guessing. You might get a better indication of engine performance by utilizing the sound of the engine.
The best way to tell if your engine is producing enough power with a fixed pitch prop is using your tachometer. One is required for all flight in a powered civil aircraft with a standard category U.S. airworthiness certificate in the US by 14 CFR 91.205. With a constant speed prop, you are required to have a manifold pressure gauge to indicate the power output of the engine.
On the other hand, even if you could judge your engine output without instruments, it still would not account for the effect of density altitude on the lift producing airfoils. Instead, you are better off determining density altitude using the weather data that you should have reviewed during your preflight planning required by 14 CFR 91.103. For that, you need no aircraft instruments.


What is the purpose of the sharp pods under airliner wings? What are the pods with the sharp trailing edges underneath the wings of large airliners, as shown in the image below?

My best guess would be fuel tanks

They are Anti-shock bodies.

In the transsonic speed range (above about Mach 0.7), aircraft drag is governed by Whitcomb area rule, which basically says that to minimize drag, the aircraft cross-sectional area must change as smoothly as possible, independent of its actual shape. It is somewhat counter-intuitive, but well established.

Compare this Junkers patent drawing (via Wikipedia):

which shows various combinations of positioning engines to adopt the area rule.

For the usual aircraft design the cross-section increases over the engines that hang ahead of the wing leading edge and then the thick part of the wing and wing box (the thicker part of fuselage where wings connect), but the wing tips are too thin and the cross-sectional area would decrease too quickly, so something needs to be attached to the trailing edge to make the reduction of cross-sectional area smoother. The anti-shock bodies are usually conveniently combined with flap actuator and track fairings.

There are however some aircraft that have anti-shock bodies combined with other functions, e.g. Tu-134 (and many other designs by Tupolev Design Bureau) retracts landing gear in its anti-shock bodies (which are just one large on each side):

The flap actuator and track fairings exist on all aircraft that have flaps that extend aft as well as down (Fowler flaps and their double-slotted variants), but on slower planes they are much thinner. Compare e.g. ATR-72, which does not need to be area-ruled with its maximum Mach 0.55.


Can a commercial pilot decide where to make their turn after departure? If there aren't published vectors to tell a commercial pilot which heading to take as they climb, can they decide where to make their initial turn on their own or would an ATC always involved in where they make the turn?

The short answer is yes, a commercial pilot can make a decision when to turn.

To clarify a few points though, there really isn't such a thing as a "published vector".  If a departure procedure with heading were to be published it would then become a Standard Instrument Departure, or SID.  True, some SIDs will specify radar vectors, but this simple tells pilots that they should expect ATC to assign headings that will vary depending on traffic, not which heading they can expect to actually fly.

Next, "commercial" pilots don't do anything different than private pilots, airline transport pilots, or military pilots.  When and where you turn during departure depends primarily on whether you are operating under IFR or VFR.  Secondarily, decisions on when to turn will be based on terrain, noise abatement, company policy, and lastly personal preference.

So, considering my answer in light of the above, there is a big difference between a 737 operating IFR on a SID, and a commercial pilot in a 172 towing a banner under VFR out of a non-towered airfield.  If you have a specific scenario you are wondering about you might get a better answer if you can narrow down the question.


How is crew resource management trained? Pilots are taught that pilot monitoring should speak up if something seems wrong, and take over the controls if the pilot flying does not respond adequately, even if the pilot flying is a senior captain. However, do they actually train such situations?

For example recently a final report for accident of US-Bangla Airlines flight 211 was published. The accident involved a badly disoriented captain trying to salvage a really botched approach, and while the rookie copilot did try to be helpful, neither she nor the tower controller was assertive enough to explicitly call go-around.

I would think that some practical training would help in this kind of simulation. I am thinking of a simulator session that would start with the instructor being pilot flying, doing something wrong and acting confused and expecting the trainee to intervene appropriately. The trainee would know the instructor expects them to intervene, and thus wouldn't have qualms about it, but the trained reaction would still help overcome interpersonal issues in real flight.

CRM training which I have been exposed to consists of lecture/videos to cover principles and expand on them with techniques.  There may be some classroom exercises.  However, due to the way that most training is conducted, the "classroom" is usually small numbers.  The application of CRM is in the simulator (SIM), where evaluation of techniques can be provided as the techniques are applied in routine and not-so-routine training scenarios.  Debrief is normally instructor(s) on team, after the SIM session(s).

For the training I get, CRM is pretty effectively integrated into recurrent SIM training.

For ab inito and primary training, the CRM training is similar, with classroom/video training.  Flight schools and academies will have larger class sizes and normally have quite a bit of depth in their training. I recently reviewed a 4 credit hour university course on CRM.

A friend who is a pilot, and also an Emergency Medicine Physician, (and with graduate and undergraduate degrees in Human Factors and Industrial Engineering) has been applying CRM to the hospital emergency department operations, and the military has similar efforts.

CRM has been around for a long time, although there were cultural impediments to it's widespread integration in the aviation context.  Much of that continues to change over the last 20 years.  I expect that CRM will expand into areas such as varying personality styles and other team techniques in the future. An example is some of the people style recognition and skills as developed by Robert Bolton, PhD and Dorthy Grover Bolton.

To summarize, the method of teaching is dependent upon the venue.  In many areas of aviation, CRM is integrated into recurrent training and critiqued on observed operations.  In initial training, the introduction of CRM is largely dependent upon the style of instruction, and whether that instruction is individualized or team based.


How should I make a downwind departure from a towered airport? I'll be departing from a towered (Class D) airport, and I need to make a left downwind departure and turn right off the downwind leg to exit the pattern.

I've done this with a CFI, and I've also made left crosswind departures, and each time I climbed at full power above the traffic pattern altitude (TPA) while still on the downwind/crosswind leg, and I exited the downwind/crosswind leg whenever I felt like it.  I never really thought about whether I needed to stay at TPA all the way to the end of the leg, or whether I needed to complete the leg before exiting.

Do I need to stay at TPA while in the pattern, or can I climb above TPA since I have told the tower I plan to depart?  And when can I leave the pattern?

Typically, you have to think about each phase of flight in three dimensions (sometimes four if you consider time and timing of maneuvers). To be “in the pattern”, you have to be within the patterns lateral boundaries (not the right terminology) and at the proper altitude.

I consider myself to be in the pattern within a mile of the runway and below 1500 feet AGL. At this distance, I can still affect a power-off landing if my engine quits. Although the airport might designate a specific direction for the pattern, I consider either side of the runway as being in the pattern. This is just in case ATC gives instructions to fly counter to the typical pattern, or another pilot does not know the designated direction.

When exiting the pattern, you follow ATC instructions. They even have the prerogative to have you cross over the airfield abeam midfield when you are on the downwind. In the absence of ATC instructions, your best practice is to do one of three things. They are...

Continue straight out on the same course as either the departure leg or the upwind leg. Sidestepping to the upwind leg should get you out of the way of traffic landing on the opposite runway (same pavement). Once you are two or more miles away or above 1500 feet AGL, you can turn to your planned heading. If your desired heading will take you back over the airfield, try to be above 2000 feet AGL.
Once you are past he departure end of the runway, turn in the general direction of the traffic pattern. Keep your turn between zero and ninety degrees while continuing to climb out. Once you are two or more miles away or above 1500 feet AGL, you can turn to your planned heading. If your desired heading will take you back over the airfield, try to be above 2000 feet AGL.
Remain within the lateral track of the airfield during your entire climb to at least 2000 feet AGL. Once you are two or more miles away or above 1500 feet AGL, you can turn to your planned heading. If your desired heading will take you back over the airfield, try to be above 2000 feet AGL.


What is the difference between a monocoque and semi-monocoque fuselage type? What are the main differences between these two types of fuselages?

A monocoque fuselage has its skin holding the skeleton structure together while the semi-monocoque has both the skin and the skeleton holding together. Semi-monocoque also has "stringers" running horizontally down the plane to help hold the frame together. The monocoque fuselage also cannot be used for airframes after a certain size (small aircraft with single engine), but the semi-monocoque has been used from single piston engines to commercial airliners.

A monocoque design would also have a safety risk involved if the skin was damaged because it is the load-bearing structure.

Image and some text source


Is there a typical time on site during an investigation of a major accident? An answer to the question Why does it take months, sometimes years, for the BEA and NTSB to complete aviation accident investigations? said,

  Visiting the Site - First there will be a team that heads to the incident site to collect information. If the site is easily accessible, this may be a fairly quick process. If the site is tough to access, or takes a while to find, this will of course take much longer. This is generally the part most visible to the public, but is only the tip of the iceberg in generating a useful report.

When the site is easily accessible, what is the typical (or average) amount of time spent on site collecting data of a major accident?

There are simply too many variables to answer this question, even in general terms.  And wreckage accessibility is just a small part of it.

If an aircraft runs off the end of the runway and the pilot survives to make a statement that can be corroborated by another crewmember, tower and other eyewitnesses, as well as weather reports, it doesn't take much time to wrap things up.  Probably a few days is all that is actually needed on-site.  Most of the work at that point is administrative in writing the report.  The aircraft may even be mostly intact and towable.

However, when all you have is a smoking hole in the middle of a pasture, as accessible as the wreckage may, be the investigator's workload is massive.  Sifting through all the broken pieces, numbering and cataloging them, plotting locations in the debris field, etc. can take months in itself, and then the real investigation begins.  Not to mention the cleanup.


Why don't helicopters prefer shorter rotors with more blades? My understanding of helicopters is that, despite theoretically increasing efficiency, longer blades are worse in practice than short ones in every respect (except, perhaps, cost):

Longer blades are more prone to vibration and resonance dynamics, if for no reason other than that their rigidity is reduced by length, holding all else constant.
Longer blades provide less operating clearance.
Longer blades not only stall before shorter blades (retreating), but also hit the Critical Mach number at lower air speeds (advancing).
Fewer blades require higher rotational speeds for a given "rotor disk" area, which is inefficient from not only an aerodynamics perspective but also, presumably, a transmission-and-control perspective.

But all helicopters have few blades of significant length.  So: What are the advantages of longer blades, or disadvantages of shorter blades, that lead to the rotor designs in common use?

I would imagine that in the limit it would be optimal to run something more like a ducted turbine segment, where the swept area is virtually covered in blade surface (i.e., maximizing the number of blades over the swept disc).

Noting that in practice blade size seems somewhat proportional to the body size of the aircraft, I'll deduce that in practice the bulk of the downforce needs to be generated some minimal distance away from the aircraft's body, though with some attention to the body's vertical aerodynamic aspect it seems like that could be reduced.  I guess tilt-rotors could support this hypothesis since their rotors are positioned at a distance from the body and they use smaller rotors, although it seems like they still use blades as large as possible given the wing size and body configuration.

The rotor works by accelerating air downwards, therefore creating an upward reaction force on the blades that lifts the craft.

The lift force is equal to

$$L = \dot{m}\Delta v$$

where $\dot{m}$ is mass flow rate through the rotor and $\Delta v$ is the change of speed of the air. To accelerate the air to that speed, it has to give it kinetic energy. This requires power

$$D = \frac12\dot{m}\Delta v^2$$

(the induced drag).

Now a rotor with smaller diameter will be able to affect less air, so the $\dot{m}$ will be lower. To produce the same lift, it will need larger $\Delta v$ and therefore it will need more powerful engine (up to a point, because longer blades will have higher form drag that will eventually outweigh the reduction in induced drag) and, more importantly, burn more fuel.

The blades, like wings, affect air to a significant distance above and below them, so you don't need many blades to use all air within the rotor area. But no matter how many blades you add, they will still only affect the air within the rotor area, so the efficiency won't change much.

As far as tiltrotors go, they have relatively small rotors and that makes them awfully inefficient in hover. But they don't spend most of their time hovering, they spend most time flying somewhere and in the fixed-wing mode they are faster and more efficient, which outweighs the worse efficiency during take-off and landing.

See also: Is there any equation to bind velocity, thrust and power? (via Energizer777's deleted answer).


What are these "lines" on the A319 flaps, are they damaged? I've noticed a grey line on the flaps of the A319:

What is that?
Source

You are seeing the steel reinforcing sheet metal at the line where the spoilers rest on the flaps when both are retracted.  It is there as a bearing surface since there is some inevitable contact between the spoilers and the top surface of the flap when they are both retracted during flight.


What are the requirements to obtain an FAA private pilot's license in Bosnia? I'm a US citizen currently living in Bosnia. Before I left the states, I was working on getting my PPL.

I currently have about 65 hours and was very close to finishing, but I was unable to do so before I left because of inclement weather and preparing for the move.

Would I be able to finish getting my license in Bosnia?

Are flight requirements the same? Would the flight hours transfer?

If I complete my license here would it be valid in the states?

You would have to find a US-licensed CFI in Bosnia to give you the training, and then a Designated Examiner in Bosnia to give you the oral and practical exams. The first may be doable, the second pretty much impossible unless you want to pay someone to come to Bosnia. Certainly it would be much easier (and probably cheaper) to come back to the US for a few weeks and do nothing but finish your ticket.


What are the pros and cons of practising figure-eight landings on perpendicular runways? This is just a gee-whiz question, I have no intention of doing this nor am I trying to get anyone's blessing on this.

Part of remaining current to legally take passengers up in a plane is having 3 takeoffs and landings within the prior 90 days. There are also night requirements requiring 3 full-stop landings within the prior 90 days.

Some folks who don't fly often but want to take passengers up will hop in the plane and do 2 touch-and-goes and a full-stop before picking up their passengers. Those same folks might like to be thrifty and do those laps of the pattern as quickly and tightly as possible to minimize tach/hobbs time.

Here's what I'm getting at. If you were based out of an airport with 2 near-perpendicular runways, the winds were calm, and the traffic was nearly if not completely dead, could a pilot do figure-8 shaped landings so that the traffic patterns were halved? This would obviously involve alternating between left- and right-traffic, so those considerations would have to be made as well.

CONS/RISKS:

At an uncontrolled airport, there is some risk of surprising a plane that's not communicating. However, that risk is really not all that different than normal uncontrolled operations.

At a controlled airport, you'd have to get the controller's permission. Unless there's a specific regulation, though, I don't see why they couldn't clear you to land on 09 after taking off from 36.

PROS:

The whole point of these takeoffs and landings is to ensure that you as a pilot are safe to land on runways in general. Taking off and landing 3 times on the same runway does accomplish this, but adding another runway in there makes the currency more "general", especially if there are differing runway surface materials, lengths, widths, etc...

I did assume the winds were calm, but if the winds were something like 5kts, you would also get the experience of having a crosswind. This is great because you might be taking your friends to an airport with one runway, which could mean you have no choice but to deal with a crosswind component. You don't want your first shot at this in 90 days to be with friends in the back!

There's nothing stopping you from doing this at an untowered airfield, at least in the US, UK and most of the places I've flown to. There just isn't any benefit. What you should be looking to do is keep up the practice you need to fly safely, which is the spirit of the law rather than the letter of the law which is to maintain currency within regulation.

Could you fly some weird-ass pattern and save about 5 bucks? Sure! Does cutting corners make you a pilot I'd fly with? Absolutely not, because you are looking for ways to economize rather than fly diligently. Flying the pattern is good because it puts you where other pilots expect you and keeps you out of conflict, it also means you know what to do when you arrive at an airfield for an approach. If you're constantly flying some strange bent figure-eight you're bound to mess it up and that could get you into trouble. Take-offs and landings are the busiest and most dangerous times when flying, the whole point is to standardize and reduce risk, if you are flying to a different runway every time the approach constantly changes which isn't good. A good landing comes from a good approach, which starts from a consistent circuit.

Flying the same pattern is also good for your practice and improving your technique. Flying repeated patterns with the same wind conditions means you practice in those conditions until you nail them. It allows you to hone your technique. If you have a different wind, runway and visual cues every few minutes you don't get the consistency to learn what you're doing wrong and improve it.


Do designers use the same RAM (Radar Absorbing Material) coating across the length and breadth of a fighter aircraft? I was looking at this image:

Image from Wikipedia

and couldn't help notice that the RAM coating looks different on the vertical/horizontal stabilizers and wings compared to the fuselage.

Given the fact that there are different types of RAM, such as iron ball paint absorber, foam absorber, etc... Are different types of RAMs being used in order to achieve stealth?

According to this article and this book, they use a greater amount of wide-band structural RAM on the wing's edges, whereas they use a ceramic-matrix RAM on the exhaust nozzles. Not only is that the case, but the actual edges have proprietary material designed to be stronger, and have a different radar signature. Although, what you're seeing is probably a combination of the paint job as well as the material, considering the F-22's stealth is not only an aspect of radar, but also visibility.

Most of the stealth of the F-22 comes from the physical shape of the F-22, and reducing its radar cross-section. There are also specialized materials that assist in obscuring its infrared signature. The topcoat, a type of paint, assists in reducing the infrared signature, especially.


Why would a cylinder not work below a certain RPM? We have an IO 540 Lycoming engine, and cylinder #3 doesn't work below 1900 RPM (cold to the touch; EGT and CHT are zero; no vibration). The engine is new, what could be the cause(s)?

We cannot contact the company.

Well, if it is cold and cht and egt are zero then I you're either not getting spark or fuel or air.

It's possible that the spark plugs are not firing.  Clean and bench test them.  Also check that the mags are timed correctly.   Maybe they work but they just fire at the wrong time.

Make sure the valve train is assembled correctly.  When you installed the cylinder, did the lifters and rods get put back correctly.  Also, are the rockers installed correctly.  I know this sounds like a stupid thing, but sometimes people make errors.

Maybe you have a stuck or broken valve.  You typically notice when this happens though!  Also, if it works at some RPM and not others, this is probably not the issue.

Finally, have your A&P follow Lycoming's fuel system calibration procedure to the letter (you'll need to look this up; TCM's is SID 97-3).  I had a TCM IO-520 on a V35B for a few years and when we calibrated the system we saw a noticable improvement in engine performance.

Of course, check the compressions!  If you're 0/80 then you may have your answer right there.

These are just a few thoughts and it's by no means a comprehensive list of possible causes.


Can an experienced airplane spotter identify planes only by sound? I come from a background in railroad watching, and often times one can identify the maker of a railroad locomotive purely by sound.  Maybe not the exact model of locomotive, but at least what type of diesel engine is in the locomotive.

Although there is a similar question here: What could cause GE and Rolls-Royce turbofan engines to sound different?, my question is whether an experienced airplane spotter could be near the end of a runway at a busy commercial airport and be successful in identifying the model of commercial jet aircraft landing and taking off only by the sound the spotter is hearing from the aircraft as it flies overhead?

To me as an inexperienced airplane spotter, they all sound similar.  But to airplane spotters, all railroad locomotives may sound the same too.  :-)

Yes it is possible, although it is kind of hard to prove it over the internet.

Generally the type of engine (propeller / turbo-fan / turbo-prop etc.) is quite easy to distinguish as they make very different sound. I can also tell a Rolls Royce engine from others because Rolls Royce engines make a quite "harmonic" and "warm" sound as it powers up.

Now here is the fun part: I correlate the sound with the type of the plane by comparing the Doppler effect as the plane passes by. It tells you how fast the angular velocity is in relation between you and the plane. The variation in loudness gives you the approximate distance to the plane - if the plane is far away, its loudness would change slowly. Combine that with the geographic location of yourself and the flight paths of planes, it gives you the speed of the plane.

The speed of the plane is important because it tells you the size of the plane. If I hear a loud multi-prop engine moving slowly, I'd bet a transport plane, something like a C130. If it is moving quickly, I'd bet an aerobatic aircraft.

The location where I live is directly under one of the SIDs of a major airport. Planes are usually ~3,000 feet when they pass above me. One thing I notice is that long route planes like Boeing 777 or Airbus A340 makes a noticeably louder noise. This is because these planes carry a lot of fuel on takeoff, and their climb performance is restrained compared to short haul airplanes, meaning they pass above me at a lower altitude, hence the louder noise. I cannot distinguish from sound if it is a B777, B747, A330 or A340, but I know it is not a B737 or A320 unless the pilots fly slow and low.

I confess I have an unusually good hearing ability. I often hear faint sound or noises which others cannot notice. I am also a musician.


Why don't passenger planes move back by their own means before taxiing? As far as I know, passenger planes needs a puller/pusher truck to go back in the land. But why they don't go back without truck assistance?

I’m not exactly sure, but it sounds like you’re asking why planes need a tug on pushback. Some jet and prop planes such as the 727 and MD-80 can perform a power back where they start at the gate and use reverse thrust to exit it. This procedure was more common in the 70s and 80s but seems to have died out in the 2000s. According to wikipedia the practice was stopped to save fuel. Additionally, there was a high risk of foreign object debris entering the engines from the ramps. Thus, the procedure was even less common on low engine aircraft such as the 737. The C-17 performs powerbacks still for the armed forces, so size is not a limiting factor.

You can check out a video here of an MD-80 powerback.


Where are US FIS-B UAT ground facilities located? In the US there are Flight Information Services Broadcast (FIS-B) transmitters strategically located to provide WX, NOTAMS and other flight information utilizing the ADS-B infrastructure. ADS-B has two physical layers, being the Universal Access Transceiver (UAT) and a 1090 mHz Extended Squitter (1090 ES). FIS-B utilizes the UAT, which are located at 978 mHz.

These UATs are intended for ADS-B use, as well as FIS-B, and additionally Traffic Information Service (TIS-B). They are primarily designed to service traffic below FL180. While they are not deployed to cover all locations, some design goals of the system include having CONUS enroute coverage.

The FAA publishes a coverage map, however, it has apparently not published a list of ground UAT sites. It would be possible to scrape UAT sites and develop a database of ground facilities, however, no one has published the results of doing so, at least that I am aware of.

Having such a list would be helpful to operators such as pipeline, geophysical, agricultural and other operators who tend to fly low, yet may still wish to have FIS-B (and perhaps TIS-B) services, or at least predict where they might be available.

Furthermore, the FAA has said that there is no security provision restricting the disclosure of UATs for FIS-B.  However, they have declined releasing a list of such ground facilities.

Where are the FIS-B UAT ground facilities, and has anyone compiled a list and published it for general access?

The FAA does publish a list of towers but no locations, only a generic coverage map.

However, the towers do broadcast their own location, and some Stratux users have collected that data and turned it into a map.


Is the whole world's airspace covered by ATC? I'm an enthusiast and have only flown flight/atc simulators (on the VATSIM network). Obviously sometimes the airspace you are flying in is not covered by any ATC (so I have to set my frequency to Unicast). And very often there is only the tower of an airport available. How is it in the real world?

Is the whole world's airspace covered by ATC at all times?
Is any airport covered by all its layers of ATC (Delivery, Ground, Tower, ...) at all times?
How often do pilots use the Unicom frequency because there is no ATC available in current airspace?

The entire world is divided into Flight Information Regions (FIRs), so in theory there is someone responsible for everywhere.  However, those FIRs are then subdivided into different classes of airspace.

Class A/B/C/D/E airspace is "controlled", meaning there should always be some sort of ATC available.  In remote areas, though, ATC may not have radar coverage, so separation would be based only on position reports (plus ADS-B, for participating aircraft).

Class F/G airspace is "uncontrolled"; any ATC service would be advisory only, and around untowered airports, they'll tell you to use CTAF.  Often the reason airspace is uncontrolled in the first place is a lack of radio and/or radar coverage.


Why wasn't the Boeing 737 grounded in 1991 after a crash's cause remained unknown? Why weren't 737-200s (and other variants):

grounded immediately after UA 585 crashed, out of precaution and risk avoidance? The crash's cause was unknown then.
remained grounded in 1992, after the NTSB

  was unable to conclusively identify the cause of the crash[?]

It feels foolhardy to allow an airplane to be airborne, when it still suffers from an unknown fatal flaw.

If the cause of the accident can't be established, it can't be established it's due to a flaw in the aircraft itself, let alone a flaw in the aircraft design that affects the entire fleet.

For example there was an accident involving an aircraft where a careless maintenance worker had installed the wrong screws to refit a cockpit window. In your scenario the entire fleet would have been grounded instantly after the accident, pending investigation.In this case they found the cause of the accident after a few weeks, but in other cases it could take months or years and ruin not just every single operator of the type but the manufacturer as well.

Think MH370 for example. That one went down several years ago now and no wreckage was ever found to investigate. In your world that'd mean that every single Boeing 777 the world over would have been grounded now for several years and probably will never be allowed to fly again because it's extremely unlikely they'll ever find the wreckage, let alone in a state that will allow the determination of the cause of the crash.

In the years since, there's been 1 other crash of a Boeing 777, and that one due to external forces (a missile fired at it by the Russian army) completely unrelated to the aircraft itself.

Now, if there'd been a number of unexplained accidents due to mysterious causes in short order across operators of the same type, it's quite possible that operators, manufacturers, and regulators would step in and decide to suspend operations of that type pending investigation. But a single accident? No.


Does bypass air produce thrust? How does bypass air exiting the bypass nozzle produce thrust in a turbofan engine?

I thought that thrust was produced by air reacting with the fans. So if thrust happens when there is an action-reaction pair with the air and fan blades, is there additional thrust provided when the mass of air pushed back by the fan blades exits the back of the engine?

You can model the fan disc driving the bypass air flow as a well-shrouded propeller inside a short duct. It does indeed generate thrust which, as in the general case of a propeller, is transmitted to the engine case via a thrust bearing that supports the fan disc and thence to the airframe via the engine mounts.


How does a pitot plate work? I understand the basic concept of the pitot tube in that it measures the air pressure coming into the tube in order to compare it to a static pressure measured elsewhere on the aircraft.

The B-2 bomber, however, has pitot plates in order to eliminate the radar reflectivity of the pitot tube.

How do these plates work, as compared to tubes, and why aren't they more common, since a flat surface that is less radar reflective would also, likely, be more aerodynamic?

The B-2's pitot plate has actually been the cause of an accident in conditions that may or may not have had the same effect on aircraft with pitot tubes.

Pitot plates work much like pitot tubes; they measure the pressure of incoming air. The main difference is just how they measure it: pitot tubes measure the ram force of air while pitot plates measuring how much air is constricted by an obstruction. Pitot plates direct air through a "plate" with a hole that impedes the flow almost like how a Venturi tube accelerates fluids. Pictured: Pitot/Orifice plate

Pitot tubes are easier to maintain, inspect, and install. Some of their main problems that you might not encounter with a pitot plate, such as icing, are countered with tested and approved safety systems (like heating). In addition, pitot tubes are not the only instrument to measure airspeed; most commercial and GA aircraft use pitot-static systems in which other pressure sensors are used to get a better and more reliable reading. Pitot plates are advantageous in that they reduce air pressure about 5:1 rather than the pitot tube's 10:1 (meaning yes, less drag in some sense) but on such a tiny scale it makes barely any difference. On the flip side, pitot plates have very inaccurate readings at lower speeds (though so low that it probably would not matter for any jet aircraft). Also, it is to my knowledge that pitot plates are used mainly for fluid research, sometimes not even related to aviation.

Since pitot tubes are relatively small compared to the size of an aircraft and are streamlined anyway, there would be little to no noticeable improvement in aerodynamics. You would think that jetliners have completely clean surfaces, but guess again:

Removing a pitot tube won't make a difference. Note: the gray circles outlined in dotted red boxes are pitot-static ports, which, combined with an aircraft's pitot tubes, make up the pitot-static system. They can measure air pressure for both airspeed and altitude among other things.

Final thing I wanted to clear up: flat surfaces are generally less aerodynamic than curved surfaces. Someone got too much of that idea when designing this plane... /s


Does an FAA pilot certificate qualify as an ICAO pilot licence? What is an ICAO pilot license?

I've seen it as a job requirement before, does my FAA ATP count?

My understanding is that most FAA licenses would also qualify as "ICAO Licenses" (certainly the ATP seems to as we have a bunch of US/FAA certificated ATPs acting as international captains for US airlines flying to/from ICAO member states). From a quick read I think anything from Private up meets the ICAO Annex 1 (personnel licensing) requirements. (It appears that ICAO charges for Annex 1, but the fine folks in the Republic of Serbia have made the 2011 edition available on their Civil Aviation Directorate's website for us to all read and enjoy).

In addition to the Annex 1 requirements, ICAO's FAQ has the following to say about licensing:

  ICAO licence or international licence

  ICAO does not issue any licences. Licences issued by ICAO Contracting States on the basis of Standards and Recommended Practices of Annex 1 – Personnel Licensing, are habitually called ICAO licences. This has led many to believe that there is a specific ICAO or international licence. The fact is that there is not one single international licence issued by ICAO or any other organization. States issue their own licences based on national regulations in conformity with Annex 1 specifications and validate licences issued by other Contracting States on the basis of bilateral or multilateral agreements or the fulfilment of nationally legislated requirements.

and

  International recognition of flight crew licences

  The Convention on International Civil Aviation, often called the Chicago Convention, provides for worldwide recognition of flight crew licences issued by any member State of the International Civil Aviation Organization (ICAO) provided that:

  the licence meets or exceeds the ICAO licensing Standards of Annex 1 – Personnel Licensing to the Convention on International Civil Aviation; and
  the licence is used on an aircraft which is registered in the State which has issued or validated the licence.

  If the licence is to be used on an aircraft which is not registered in the issuing State, the licence holder must obtain a validation of the licence from the State of Registry or alternatively obtain a new licence issued by the State of Registry.

So basically your US/FAA license is a valid "ICAO License" as long as you're flying a US-registered aircraft & the nation you're flying to/through accepts US/FAA licenses (possibly with some additional requirements on a per-country basis).

If you got a job for a Serbian airline and needed to fly an aircraft registered in Serbia you would need the Serbian Civil Aviation Directorate to issue you a license (or validate your FAA license) because they are the state of registry.

From what I've read you can get a private license issued pretty easily in most ICAO member states - the procedures are roughly analogous to US FAR 61.75 - but if you want anything more than that there are other hoops to jump through to "convert" your license, which can range from just a written exam to a full-fledged checkride or more -- this is probably what people are referring to when they say it's difficult to get an "ICAO License" issued.


Can the fly-by-wire system of a modern airliner handle an unstable condition? According to this answer airliners/large passenger aircraft such as an A320 are designed such that they are longitudinally, statically stable under normal flying conditions.

What if, for some reason, the c.g. would suddenly shift just aft of the neutral point? Could the FBW system of (for example) an Airbus handle this, just like the FBW of a fighter jet which is unstable by design?

Of course I'm not talking about a situation where the c.g. ends up so far back that the aircraft enters a deep stall, but a condition just "after" neutral stability, where the aircraft has just become "slightly unstable".

Yes it can - to an extent, depending on:

amount of CG shift;
airspeed;
aircraft weight (actually Moment of Inertia);
maximum deflection rate of elevators/ailerons.

If the airframe has aerodynamic static stability, a disturbance in Angle of Attack Creates aerodynamic forces that return the aircraft attitude back to neutral. If the Centre of Gravity shifts aft of the neutral point, the airframe becomes statically unstable - the aerodynamic forces now want to amplify the disturbance. The rate gyro's in the fly-by-wire system sense that the attitude deviates from the commanded attitude, and deflect the elevators/ailerons such that the aircraft is brought back.

Image source

Amount of CG shift
The ability of the Flight Control System to correct for unstable equilibrium depends on the degree of instability: the curvature of the right cup in the picture above.

Airspeed
Deflection of the elevators and ailerons generates aerodynamic moments proportional to $V^2$. At high airspeeds, a small deflection results in a large moment about the CoG - the critical situation is low airspeed, which mostly occur close to the ground. At low airspeeds large deflections are required.

Aircraft weight
If the aircraft is at a high gross weight, and if this weight is distributed away from the CoG, larger control deflections are required to correct disturbances in AoA. A heavier bowling ball in above picture makes for higher required forces.

Maximum deflection rate of elevators/ailerons
The frequency response of the flight control systems is a function of how fast the control surfaces can be brought to the required position, and this is a function of hydraulic fluid supply rate: the added capacity of all the operational hydraulic pumps.

The F-16 is designed to rapidly correct for any disturbance from the commanded attitude, in any flight situation. All systems are dimensioned such, that artificial stability can still be provided at the lowest airspeed and the highest MOI that the aircraft can encounter. The A320 is not designed with a flight critical FBW system - if all systems fail, the aircraft returns to a state with aerodynamic static stability. If the FBW system fails in an F-16, the pilot must eject.


How does wing aspect ratio influence lift and drag? I know simmilar questions are all over the internet (and this website too), but there's one thing that i just cannot comprehend and none of the articles i read could explain it properly.

According to wikipedia the coeficient of drag depends on the aspect ratio by the following way:
$$
C_D=C_{D0}+ \frac{(C_L)^2}{\pi e AR}
$$
But when i search why does it have this negative impact, i read things like "high AR creates stronger vortices at the tip of wings, which reduce lift".
But reducing lift reduces the numerator of the expression, so that should in fact REDUCE the drag. Does the $C_L$ somehow also depend on $AR$? If yes, is the dependancy also linear or less?

And another thing that blows my mind are statements, that wing which spans the  whole width of a wind tunel produces no induced drag, because it has no wing tips. Are you telling me that the induced drag is only caused by wing tips?
From the pictures at How complete is our understanding of lift? one would think that drag is natural part of lift and is caused by the airfoil even in 2D without considering wingtips.

So to sum up, can you please properly explain me:

How does the aspect ratio influence induced drag, why is the AR in
denominator
How does it influence lift
What really happens at the wing tips
What happens in the wind tunel on a wing that spans its
whole width

Your suspicion is leading you in the right direction. A lot of what you read on the Internet about induced drag is at least misleading if not blatantly wrong. But it is repeated by sloppy authors who don't ask the right questions.

If you have read stuff like "high AR creates stronger vortices at the tip of wings, which reduce lift", you hit such a completely wrong statement. The misleading version of it is high AR creates weaker vortices. For a hopefully better explanation, please turn to this answer.

Now to your questions:

  How does the aspect ratio influence induced drag, why is the AR in denominator?

The surprising answer: It is the lift per unit of span and the inverse of the square of flight speed which determine induced drag. Another influence is the distribution of lift over span, but aspect ratio does not play a role. See this excellent answer by @DeltaLima for an explanation, or this one for a longer one.

  How does it influence lift?

Indirectly, by increasing the lift curve slope.

  What really happens at the wing tips?

On the top side, suction turns the airflow inwards so the air gets a rotational component and some of it flows around the tip from bottom to top. Due to the small wingtip curvature, this vortex has low pressure at its core (and lets air condense early), but is overall weak and rather insignificant. The real trailing vortex results from a rollup of the wake, but even this does not create drag.

  What happens in the wind tunnel on a wing that spans its whole width?

Please read the answers to this question.


Why was "taxi into position and hold" changed to "line up and wait" in the USA? How come taxi into position and hold changed into "Line up and wait?" Did the old phraseology cause misunderstandings, or did it seem dated?

To ensure international consistency. Line up and wait is the standard phraseology used almost everywhere in the world, as defined by the ICAO, so it was confusing for pilots that another phrase was used to mean the same thing when flying to the USA.


Why do wings prefer laminar flow if cd is lower for turbulent flows? Can anyone please explain to me why we prefer to maintain laminar flow over wings, despite the fact that the overall coefficient of drag appears to reduce as the Reynolds Number increases? I have read that turbulent flows lead to increased skin friction drag, but this is hard to internalize given that the cd is lower overall in turbulent flows for the same angle of attack.

I've been trying to do some research to better understand why aircraft are designed this way, but I haven't had much luck so far. If anyone can offer me some insight here, it would be greatly appreciated!

As an example, I thought it would help to include the drag polar for the NACA 0012, obtained from airfoiltools (http://airfoiltools.com/airfoil/details?airfoil=n0012-il).

Laminar flow and turbulent flow are not directly linked to Reynolds number, even though Reynolds number is a heuristic indicator of when the flow may transition from laminar to turbulent. However, the transition is actually not well-understood and is difficult to model/predict. That's why you will see cases where, for the same Reynolds number, one flow is laminar and another is turbulent.

Let's take a flat plate for an example. The flat plate boundary layer in laminar flow actually has a closed-form solution; the skin friction drag is given by:

$$C_{f}=\frac{1.328}{Re_c^{1/2}}$$

As you can see, as Reynolds number increases, the drag coefficient decreases.

Turbulent flow, on the other hand, has no closed-form solution. An approximation for a smooth plate is given by:

$$C_{f}=\frac{0.074}{Re_c^{1/5}}$$

The two lines are plotted in the figure below (cited from this Penn State course, which has a pretty good summary of boundary layer results for flat plate). As you can see, at the same Re, laminar flow has less skin friction drag than the turbulent counterpart.

From a skin friction drag perspective, if you can keep the wing in laminar flow, then all the power to you. In practice, however, this is very difficult. Any un-eveness on the wing (e.g. rivets, steps and gaps) could transition it to turbulent flow downstream. Any contamination, such as insects, could potentially ruin it.

Another consideration is whether staying laminar for the whole wing is desirable from a flow separation perspective, since laminar flow separates easier than turbulent flow. There will be a trade-off amongst stall speed, high AOA handling and drag.


Why was the Bell Boeing V-22 Osprey not worked on more? I've recently learned of the Bell Boeing V-22 Osprey and it appears to be a very advanced and useful vehicle. I can instantly think of reasons why the Osprey would be successful such as:

1) It can take off in small places and land in small places unlike planes
2) It can hover
3) It can turn into a plane and fly fast
4) It can pick up things like cars without the need to carry it inside like planes
5) It can easily fly sideways and backwards

So my questions are:

1) Why hasn't the Osprey advanced/been successful. For example how the F-15 went to the F-16 then the F-35 etc.
2) What made Boeing choose to have rotors instead of the faster jet engine?

The only possible reasons I can think of are things such as:

1) Stealth/noise, the Osprey requires large rotors and probably makes double the noise as a helicopter or plane would make
2) Maintenance costs, a helicopter requires more maintenance than a plane, I'd think the Osprey requires more maintenance than a helicopter or plane
3) Cost, the Osprey probably costs more than an average plane or helicopter

Though I'm not sure of the real main reason as surely those reasons can be fixed.

The Osprey has arguably been quite successful considering the circumstances. As Energizer777 points out, the basic idea is not new, and there were many engineering challenges to create a viable aircraft. That these challenges were solved and the plane is now in production and active service seems to be a pretty big success. Also, this has all happened relatively recently. The V-22 first flew in 1989 while the F-15 and F-16 both date back to the early 1970's (and are still in active service). The challenges in refining the design pushed introduction of the V-22 out until 2007. The design just hasn't had enough time to mature past the first successful application. You might consider the civilian tilt-rotor AW609, currently targeted for certification in 2017, as the next advancement of the design.

Props/rotors are more efficient than a jet engine at low speeds. Given that the slow and vertical portions of the flight are very important to the design, this decision makes sense. The prop wash also flows over the wing, allowing the wing to be more effective with a short span. Using turboshaft engines rather than jets also allows one engine to drive both rotors if the other engine fails, making single engine operation easier.

You are right about the drawbacks of the design. The V-22 is noisy and not as agile has a helicopter in slow flight. Maintenance requirements are high and were certainly an issue early on in the introduction to service. And upfront costs are also more than a helicopter or airplane of comparable size. However, the capabilities you listed first are worth these added costs, at least to those that have purchased/ordered the V-22.


Orange object on back of jet-engine pylons, what is it? Watching this Video of a L-1011, I noticed an orange/brown object on the back of the jet-engine pylons I never saw before.

What is it?
What's the purpose of it?

Manu H is right. It is an IR jammer device. Saudi (corrected from the comment of David Richerby:)Royal Flight airliners tend to have them (root of the wing, next to the light)...


Are paper charts required for flights outside the USA? Can international flights by a US operator be performed paperless or do you need complete paper charts?

With virtually every major US air carrier today using EFB's, the use of paper charts in the flight deck has largely fallen to the wayside. Flight crews are still being provided with the exact same information, only now it is in digital form. Most, if not all US air carriers use navigational charts and plates published by Jeppesen. Unlike FAA NACO charts and plates, Jeppesen publishes charts for airports all across the world in a greatly standardized form. This allows information to generally remain similar across countries and helps to reduce some of the differences pilots operating international flights would otherwise face. Whether paper or digital, US based flight crews would likely receive charts from Jeppesen.

All of the EFB apps in use by airlines are designed to automatically provide pilots with current charts and plates needed for any given flight in the carrier's network, provided the area is covered in the chart subscription. Prior to operating an international flight, an airline (likely their dispatch department) will review their chart subscription package to ensure charts/plates are included to cover the routing, destination, and alternate(s) of any international flight. Any areas needed that are not currently included in their subscription would be added. Once added to the airline's subscription, the charts would then automatically populate to the EFBs issued to pilots. Pilots would then just need to make sure the new charts were downloaded and they would be good to go. Pilots would then be receiving the exact same information digitally that they would if they had been provided paper charts.

From a regulatory perspective, the FAA, EASA, and ICAO have all developed standards for EFBs and as a result pretty much all developed countries allow their use. As long as an airline has received the appropriate approvals and meets standards, the use of EFBs should be a non-issue. In the US, FAA EFB standards meet or exceed ICAO standards, and ICAO standards would likely be the minimum requirement while operating internationally. I am not currently aware of any country that disallows the use of EFBs for charts, but should such a scenario arise, then an airline could potentially be forced to use paper charts. However, the odds of that happening are slim to none.


Is there an FMC not connected to the AP/FD? Is it possible to have an FMC to compute the performance and navigation without having it linked to an autopilot or flight director?

Does/did such setup exist?

By definition an FMC / FMCS is linked to the auto flight system.

The closest thing to a standalone device is an EFB, but when it comes to fuel burn, and air data parameters, it's unable to compute the complex parameters since it's not connected to the air data computer and engines.

I've checked the history. From a 1985 Sperry ad:

  Since the mid-1970s, when Sperry began developing the first true Flight Management Computer System, the term "FMCS" has been misrepresented almost as frequently as it has been misunderstood. True flight management, defined by the Sperry FMCS, integrates navigation, flight guidance and aircraft performance functions through a sophisticated computer. And in today's marketplace, the "fully-compliant system" which performs exactly as specified by its user in all modes is defined only by the Sperry FMCS.

But yes, that's an ad, so I checked further back, from 1981:

  Arma boasts the first certificated airliner FMS, which is in service with the TriStars of British Airways, Delta, Gulf Air, Pan Am and Saudia. Racal-Decca Navigator is involved on the software side, and also in the support of units outside the USA. The navigation component of the FMS was derived from the earlier Mona TriStar navigation system.

That FMS was connected to the engines and autopilot, so let's check the mentioned Mona TriStar navigation system from c. 1973:

  Mona is not actually a navigation system, in the sense that it does not contain any sensor equipment. Described by its designers as an automated navigation-management package, it can readily be installed in an aircraft to serve as a direct, executive link. It is capable of processing information from the existing airborne navigation system and translating the results into the autopilot and flight director signals needed to maintain en route track, height and speed.

Even that sent AP/FD commands.

Pilot's-eye view of Mona, showing the two control and display units flanking the central electronic chart display.


How to identify an aircraft from its NC- N-number? I have the numbers from the tail NC and then down is 4686N. Its a single wing prop driven multi seat aircraft. I am unable to locate it on the federal site, hoping I can get some info here again. Thanks, Ron

Single wing prop driven multi seat aircraft? Not sure what you mean by this. A quick search on the FAA registry indicates it's a Cessna 414A.

Also, the style of tail number with NC is older, Wikipedia has an explanation of the various styles of aircraft identifications.

  An older aircraft (registered before 31 December 1948) may have a second letter in its identifier, identifying the category of aircraft. This additional letter is not actually part of the aircraft identification (e.g. NC12345 is the same registration as N12345).

An older aircraft with the same N-number on the FAA registry is the BT-13.


Can an intercepting fighter jet force a small propeller aircraft down without completely destroying it? A rogue aircraft may fly into a no fly zone, and be intercepted by standard military procedure. That involves increasingly intense attempts to establish communication. When all these fail, it may be required to force the aircraft to go down. The naive solution is to just shoot it down, which may be the right thing to do.

I wonder if it is possible for a F-16 fighter to force a small one propeller airplane to do an emergency landing? Either by making it try to get to the nearest airfield, or alternatively making it try to get to the nearest cornfield - or anything somewhat flat.

For example by disabling its propeller. By either breaking the propeller by  shooting at it, or shooting holes into the engine?

Would that work for a small aircraft?
Would it work more generally, like for commercial airliners?

An interceptor can gain cooperation from an intercepted aircraft by means of a show of force ie forming up on the target’s 6 and 9 o clock position and attempting to contact them on the emergency radio channel.  If the target remains unresponsive or refuses to comply, a fighter will often cut in front of its flight path in afterburner, causing the target aircraft to be rocked and buffeted in the jet wash.  This is usually enough to get a response from the target aircraft and compliance with the lead fighter’s or ATC’s instruction.

Any kind of intentional damage to the intercepted aircraft would not be done unless deadly force were authorized against the target.  In which case full force ie employment of weapons against the target aircraft to shoot it down would be used.

The video below is a good report on interception procedures against a civilian aircraft.  It was a joint exercise between the civil air patrol and an F-16 ANG unit.