Why did Cessna use a new design for the C162, instead of updating the C150 design? As I stare at the ceiling unable to fall asleep, airplanes are on my mind.  Failed airplanes.  Specifically: the Cessna 162.

I understand that Cessna perceived a need for a two seat trainer.  The CEO himself called that out: "The need for a modern, cost-effective two-seat trainer aircraft has never been greater, and we believe we are well positioned to meet that need."  I also understand that the light-sport aircraft (LSA) market was thought to be a significant driver for aircraft sales.  That turned out to be a gross miscalculation.  Cessna ended up selling 192 Skycatchers (versus a planned run of 600 per year) due to quality and price misses.  About 80 were not sold and retained as parts donors.  A fleet of ready-made LSA aircraft already existed (Champs, Chiefs, Cubs, T-Crafts, etc) so the value proposition of a new $150,000 LSA runabout was not compelling...or so it seems.

The following question assumes that there are folks on SE.av that have some industry knowledge of the GA manufacturing scene...

Why did Cessna not just resuscitate the proven 150 line (~24,000 built) and forego the LSA segment, given that the objective was to capture the two-seat training market and a good number of very cheap LSA airplanes already existed?

I recognize that there may be no good answer for this.  Maybe it was just one of those plausible-at-the-time business moves that didn't pan out.

I think there are a couple reasons: 1) Weight, and 2) the Type Certificate.

For #1, the original C-150 is roughly 100 lbs too heavy (in empty weight).  That's a bit over a 10% reduction, which is huge in an all-aluminum design.  Note that later models need even more weight removed (C-152 included).

For #2, the C-150 is a CAR Part 3 type certificated design.  To sell it as a LSA would almost certainly require a re-designation so as not to conflict with the original type certificate.  This is primarily a paperwork thing, but nobody had done it before (even now, none of the "grandfathered-in" type-certificated designs are still built under their type certificate or by the original manufacturer).  The C-152 is an add-on to the C-150's type certificate, so the same problem applies to it.

As far as why the C-162 failed, I think Carlo's answer covers most of the reasons pretty well (ignoring the "GA is dead" rant), though I'd like to add that Cessna did a terrible job with designing the C-162 and took so long to "get it right" that they didn't start deliveries (of an arguably inferior product) until right after the 2008 economic downturn.


What is the highest service ceiling for turboprop airplane like a Cessna 425? What is the highest service ceiling turboprop airplane,  that is fairly small, like maximum of 8 seats, and fairly cheap as well, not going over a million dollars. I looked at Cessna 425, and this plane has a service ceiling of 10km(33000ft), and this plane had the highest service ceiling, that fit the size and cost, that I could find.

So, basically , what plane out there has the greatest service ceiling, that  is small in size, like the Cessna 425, turboprop,  and cheap (under a million) ?

The PA-46-500TP Malibu Meridian can climb to FL300 and you may be able to find a high time one for under a million.

Socata TBM has a quoted ceiling of 31,000 ft and you may be able to find an older TBM 700 high time airframe for in and around a million.

In the multi-engine category:

A PA-42 Cheyenne will put you up to just under 36,000 ft and can be had used for under a million.

A Beech King Air C-90 will get you up to 30,000 feet and can be found used on the lower end of the price spectrum.


How to maintain straight and level flight after a climb? I'm new to flying and I have this question.

Suppose I'm ascending to 2000 ft. at 67 kts and 2450 RPM. When I reach 2000 ft. maybe the plane wants to keep going up, even after I lower the RPM TO 2200, for example.

How do I make the plane flight straight and level at 2000 ft? With the trim and keeping 2200 RPM, or lowering the RPM to, for example, 2100?

Attitude + Power = Performance
Performance is your airspeed, climb/descend rate, and rate of turn.
Attitude is pitch, bank, and yaw.
Power is RPM, if you have fixed pitch prop.

So how do you transition from climb to level flight? When you reach 2000ft, or maybe 1950, push forward on the yoke or control stick to about level pitch, check the altimeter to make sure you're at 2000ft, not climbing or descending.  Your airspeed will start going up. Maintain forward pressure, it is going to increase as the speed increases (you can put some trim in to help).  Once you reach the desired airspeed, reduce throttle to keep the airspeed constant.  Then use trim to take out the pressure on the yoke.

Now this will give you a workout, because if you don't know exact RPM that you need to maintain desired speed, you will be chasing it and working the yoke to keep constant altitude.  So I would lower the nose after the climb, let it accelerate, then lower RPM to 2200 and keep the plane in level flight with the yoke and trim.  After a few minutes when everything is stabilized, I would note the airspeed.  Then I would reduce RPM to 2100, retrim nose up to keep level, wait a few more minutes and note the airspeed for 2100 RPM.  And so forth.  You can build a table of RPM and airspeed.  Then, next time you fly, you will just set the correct RPM for desired airspeed.


Does counter-rotating propellers on multi engine airplanes have critical engine? I read from most of the article and books that counter-rotating propellers multi engine airplanes do not have critical engine, but it just happened to my friend who did his Commercial Multi Engine Rating check-ride that he answered there is no critical engine on counter-rotating propellers and the examiners failed him.
And one of the instructor said that he should answered both engines are equally critical.
 is there any terms that stated that counter-rotating  propellers has both engione critical?

The term "critical engine" can actually refer to two very different factors:

P Factor
Engine driven accessories, depending on the airplane and how it's configured.

A twin with counter-rotating propellers doesn't have a critical engine from a controlability perspective, but very often there are important engine driven accessories, like hydraulic pumps, vacuum pumps, generators, etc. that are only installed on one engine, and if you lose that engine, well it's more of a problem than the other one.

So you may lose the left engine and it has no effect on control or performance compared to the right, but that engine has the only hydraulic pump, so now you have to do the engine-failure-on-a-missed-approach song and dance, all while hand pumping the gear up.  Gets pretty busy.  In such a situation I'd consider the left engine more critical than the right one even though it's not a stick-and-rudder problem.

I think that's what the examiner was looking for.


Can a gas turbine be able to switch from torque to thrust? Can a turbine engine be switched from providing torque (like a helicopter) to the rotor to transfer power to provide exhaust thrust (like a jet plane)?

Related: BV-347 upgrade this way?

The main way to convert a gas turbine to provide thrust rather than shaft horsepower is to attach a large fan or propeller in place of the previous load. For example, the GE CF6, which powers aircraft such as the 747, 767, and A330, has a gas turbine variant called the LM6000 that provides around 50 MW of power.

If you want to provide thrust from the exhaust, you're talking about a turbojet, which will require a lot of changes. A gas turbine like that in the CF6 is designed to extract most of the power out of the exhaust gas to drive a load such as a fan or a generator. Just removing that load is going to cause the engine to be unstable. Each stage in a turbine engine is dependent on the stages around it for smooth operation and even small changes can cause problems. You might be able to salvage the high speed spool but the rest will have to be redesigned to provide a stable compressor section and provide most of the thrust from exhaust.

Turbojets are very loud and only start to be an efficient choice at high speeds. Even modern fighter jets are powered by low-bypass turbofans.


What is meant by "Control your descent with throttle when landing, not with pitch" I have heard it said on several occassion that when you are landing you need to control your descent with your throttle, and not with your pitch.

Two closely related questions that I think can be answered in one go:

Why do we use throttle instead of pitch to control the descent?
How does this work in practical terms?  (How do you do it?)

Your pitch is adjusted to maintain airspeed, whereas throttle and thrust are used to establish a rate of descent.

Shameless steal from KeithS comment below:

  [Y]ou're gliding down to the runway, but you need a little engine power to keep a shallow glide slope because you aren't in an actual glider. The real explanation is that trying to use pitch to control glide slope causes dramatic changes in angle of attack, especially at the lower speeds used for approach and landing. This could cause a stall, or a severe loss of altitude. The throttle provides much more minute control over your angle of attack and thus your glide slope.


When are black boxes used? Obviously, black boxes gather lots of media attention after tragic accidents where planes crash or explode mid-flight, since they could be crucial understanding the crash.

However, these are rather uncommon events.

Surely the black box could be used for other purposes like:

Helping the pilots understand a small mistake/hiccup/etc. on their flight
Monitor the plane's overall health
???

How often and for what purpose is black box data used?

There are two recorders that are mandatory on board commercial aircraft: CVR for voice, and FDR for data. They are designed to survive an accident and include an ultrasonic beacon to facilitate locating them underwater.

(Source)

It's worth mentioning that CVR and FDR are not connected to any external data port for data export/copy/extraction, and extraction of the recorders after an accident is done exclusively by the investigating agency.

(As everybody knows for years, these recorders are orange, so there is no need for journalists to continue to call them 'black boxes' as if we were not in the secret too and may not get what they are talking about...)

Cockpit voice recorder (CVR)

The CVR is a sensitive question. Crews have accepted the recording of cockpit conversations to help understand accidents. One condition is the conversations remain private in other circumstances. So there is definitely no other allowed use of the CVR.

Flight data recorder (FDR)

Certain technical parameters, like inputs on the flight controls, must be recorded, also to help determine the cause of an accident. Most FDRs record many more parameters than mandatory. Still the FDR cannot be used in other circumstances than an investigation (see section about data privacy further down).

Using in-flight data for improvement

FDR data causes less privacy concerns than CVR conversations. Safety agencies over the world have encouraged airlines and manufacturers to set up improvement programs (quality improvement) taking into account in-flight technical parameters.

(Source)

Quality improvement initiatives include:

Flight operations quality assurance, FOQA. See FAA AC 120-82.
Flight data monitoring, FDM. See Swiss FDM booklet for crews.

FDM allows companies to:

Compare their flight standards (SOPs) and the crews' actual actions. This is a way to enforce SOPs, and detect deviations from SOPs, hence crews may be reluctant to see this becoming mandatory.
Detect excessive forces applied to the aircraft, that require maintenance checks and/or repairs.
Set fuel consumption improvement actions.

As the FDR data cannot be exported, new recorders used for data monitoring and analysis are now seen on aircraft.

Quick access recorders (QAR)

Quick access recorders (QAR) are used in place of FDR, they allow much freedom, they don't have the same use and disclosure restrictions, don't have to resist a crash and can be included in wireless networks. For example this is Wifi/Ethernet QAR:

(Source)

QAR use the same data acquisition unit (DFDAU) as the FDR, using ARINC 573/717 links. They are essentially duplicating and extending the mandatory FDR, but data can be read at any time using data links. This access is not limited to investigation purposes.

Optical quick access recorders (OQAR) are QARs storing data on optical disks (e.g. Curtis-Wright), and they can record up to weeks or months of flight data. On the other hand, very small "micro" QARs exist too. This well known one uses a CompactFlash card:

(Source)

Countries like India have mandated flight data monitoring and analysis using such devices, but most regulation bodies have taken into account the reluctance of crews regarding the spreading of sensitive data, and the programs remain subject to airline decision.

Privacy aspects of CVR and FDR data

This section is likely very incomplete as the topic is complex.

ICAO:

Investigation-related recommendations are described in Annex 13 to the Chicago Convention on International Civil Aviation: Aircraft Accident and Incident Investigation.

  Non-disclosure of records. 5.12 The State conducting the investigation [...] shall not make the following records available for purposes other than accident or incident investigation, unless the appropriate authority for the administration of justice in that State [...]: [...] b) all communications between persons having been involved in the operation of the aircraft; [...] d) cockpit voice recordings and transcripts from such recordings; 5.12.1 These records shall be included in the final report [...] only when pertinent to the analysis of the accident or incident. Parts of the records not relevant to the analysis shall not be disclosed.

Flight recorder cover both voice and data:

  Flight recorder. Any type of recorder installed in the aircraft for the purpose of complementing accident/incident investigation.

However only CVR is mentioned in the article above, so there is some ambiguity about using FDR data.
The point about privacy is that if the information is disclosed, then the safety agencies may not be trusted in the future, information may not be provided, and security may suffer from this lack of information.

CVR in the US:

  A CVR committee usually consisting of members from the NTSB, FAA, operator of the aircraft, manufacturer of the airplane, manufacturer of the engines, and the pilots union, is formed to listen to the recording. This committee creates a written transcript of the CVR audio to be used during the investigation.

(Source)

  Congress has required that the Safety Board not release any part of a CVR audio recording.

(Source: ibid.).
Read also: "Privileged communications?" The bright line rule in the use of cockpit voice recorder tapes.

Recordings in EU:

Article 14, Protection  of  sensitive  safety  information in 996/2010:

  the following records shall not be made available or used for purposes other than safety investigation, or other purposes aiming at the improvement of aviation  safety: (a) all communications between persons having been involved in  the  operation  of  the  aircraft; [...]. Flight data recorder recordings shall not be made available or used for purposes other than those of the safety investigation, airworthiness or maintenance purposes, except when such records are de-identified or disclosed under secure procedures.

The article above covers both CVR and FDR, but seems less restrictive than the ICAO.

Article 34 in 76/2014:

  In order  to ensure the confidence of employees or contracted personnel in the occurrence reporting system of the organisation, the information contained in occurrence reports should be protected appropriately and should not be used for purposes other than maintaining or improving aviation safety.

Reading the many CVR transcripts available online, it's obvious that this rule has sometimes been transgressed. Authorities have now difficulties when making the proposition to increase the legal duration of the recordings from 2 to 24 hours.


What is the difference between HFEC and LFEC inspections? Sometimes we have to do High Frequency Eddy Current (HFEC) or Low Frequency Eddy Current (LFEC) inspections. My question is: what are the major differences between these two types of inspection? Which one is preferable and more economical? Which type of inspection is required in which cases?

In general, higher frequency gives better resolution of potential defects but with lower penetration into the material (depth). So HFEC is used to detect surface defects and near-surface defects, but LFEC will be required to detect deeper defects.

From this page on the NDT Resource Center website:

  The depth that eddy currents penetrate into a material is affected by the frequency of the excitation current and the electrical conductivity and magnetic permeability of the specimen. The depth of penetration decreases with increasing frequency and increasing conductivity and magnetic permeability. The depth at which eddy current density has decreased to 1/e, or about 37% of the surface density, is called the standard depth of penetration (d). The word 'standard' denotes plane wave electromagnetic field excitation within the test sample (conditions which are rarely achieved in practice). Although eddy currents penetrate deeper than one standard depth of penetration, they decrease rapidly with depth. At two standard depths of penetration (2d), eddy current density has decreased to 1/e squared or 13.5% of the surface density. At three depths (3d), the eddy current density is down to only 5% of the surface density.
  Since the sensitivity of an eddy current inspection depends on the eddy current density at the defect location, it is important to know the strength of the eddy currents at this location. When attempting to locate flaws, a frequency is often selected which places the expected flaw depth within one standard depth of penetration. This helps to assure that the strength of the eddy currents will be sufficient to produce a flaw indication.


How do airlines pay for their planes? Taking easyJet as an example, they have a fleet of over 200 A319's and A320's. At a price tag of around \$90m per plane, that equates to about \$18bn.

Given that their turnover for 2012/13 was around \$7bn, and their net profit was only \$660m, how exactly do they own so many planes? Are they financed long-term? Are they leased?

How are the deals structured for the big airlines when purchasing new planes?

The overwhelming majority of major airlines do lease at least some of their aircraft. And most airlines who choose to buy do not end up paying that full price tag.

In the case of Easyjet, around half their fleet is leased (as of 2013). Leasing allows airlines with weak balance sheets or with poor future prospects to increase capacity without locking capital.

In fact, the largest aircraft owners are aircraft leasing companies. For example, GECAS (General Electric Capital Aviation Services), the largest aircraft lessor, currently owns around 1,700 aircraft, being operated by 230 airlines around the world.

There are other (not state-owned and generally low cost) airlines, such as Ryanair, who are fond of owing most of their aircraft. What Ryanair does is negotiate very good procurement deals with Boeing (by buying large packs of planes, all being B-737s), use them for around 5 years, and then sell them before their price has gone down too low. This takes a burden on their debt levels, but seems to work for them so far on the long run.

This aircraft resell value is an important aspect to consider when comparing leasing vs purchasing, as well as tax incentives derived from amortization.

Legacy carriers (many of them state owned), on the other hand, have a tendency to purchase most of their fleet, and keeping them around for the full lifespan of the machine (around 30 years).

The actual price a company pays for a given aircraft is not public (understandably) and most figures you would be able to find are related to "list prices". However, in 2005 Ryanair was forced to disclose facts about one of the massive (by the time) purchases of Boeing aircraft. Apparently, they paid less than half of the public list price.

More current data on the actual price airlines pay for Boeing planes can be found here, where Javier Irastorza analyses the discounts Boeing is applying to their aircraft based on a balance sheet assessment.


Is there an official record of the pilot with the most logged flight time? We often hear about pilots with 10 or even 20 thousands hours. So I was wondering how much higher this number can go. Do we know which pilot has the most logged time? Is there any official number?

From Wikipedia, the free encyclopedia  John Edward "Ed" Long, Jr

John Edward "Ed" Long, Jr. (1915–July 18, 1999) was an American pilot who is in the Guinness Book of Records for the most flight time by a pilot: over 65,000 hours (more than seven years and four months) at the time of his death.

He began in 1933 at the age of 17, when he took his first and only flying lesson. In September 1989, he broke the previous record, 52,929 hours, set by Max Conrad in 1974. According to his brother, Ed Long's job involved checking power lines, so "most of that was under 200 feet, in a Piper Cub".He died in 1999 at the age of 83.*


How universal are air traffic control systems, training and practices? A commercial pilot, especially in the airline industry, is in a role that is essentially the same as that of a pilot who is employed and was trained in just about any other part of the world.

Does this also hold for air traffic controllers? How similar will the training and practices and the systems that they use in their work be?

For example:

Are qualifications obtained in one country or region recognised in others?
How much additional training would be required for a controller who has trained and worked in one European Union country, in order to take a similar role in another? Or in a non-EU state?
Would the hardware and software used by a controller in one country be familiar to a controller from another?

This question is analogous to asking, for example, how universal are law enforcement  systems, training and practices. At the highest levels you may find similarities driven by things like EU regulations, to pick one, but as you dive deeper into the implementation of those three things, you will find differences, from minor to wildly diverging. Police officers and air traffic controllers may receive very similar basic training, but once they move off from there and into the field, things can and will change dramatically.

The same explanation holds for commercial pilots. A pilot flying cargo in Alaska on Cessna 185's, for example, will be trained in and execute procedures and practices completely different than a commercial pilot flying Britten-Norman Islanders on puddle jumping routes in the Caribbean.

Bottom line is it is challenging to answer this question without context, i.e. two countries you wish to compare.


Why does my Surface Analysis chart indicates radar returns / rain when none exist? I'm using 1800wxbrief.com to get all the information necessary to brief myself on an upcoming flight.

I have noticed each time I've done this, that the Surface Analysis chart shows light / spotted rain where I can be nearly positive there is none. When cross checking this chart with sites like weather.com, it is confirmed through their weather products that there is no rain in the area.

Do these Surface Analysis charts sometimes show spotty false positives?

Fog and other low-altitude moisture often shows as very light precipitation radar returns. I look at the multi-image radar loops for an area, and if I see that I call a "sparkling" radar return in the looping image, it's a pretty good bet for ground fog. The California central valley area (around Modesto and Stockton) is known for its winter tule fog: watch the radar returns from that area in the wintertime.

You can correlate the radar observations with ground visibility observations (airport METARs, the regular and special airport weather observations, include visibility and ceiling—cloud height and coverage—information), along with satellite visible and infrared images to view cloud presence and cloud top heights. When the visible satellite shows clouds and the infrared satellite shows very low cloud tops, that's a good bet for fog or a low-level stratus layer: both have low cloud tops, typically 400'-1,000' above ground level.


What is the efficiency of running an electric motor from a gas generator? If you were to run an electric motor from a gasoline or diesel generator, how big would the generator have to be to run something like the Siemens electric engine? Is this a viable model for replacing a heavy piston engine or is it too inefficient?

The link below says standard portable generators are capable of 6.13 kWh per gallon of gas.

The Siemens only weighs 50kg and delivers a continuous output of 260kw. Does that mean I'd need a generator 42.4 times as powerful than most portable generators and be burning a gallon of gas a minute?

I know a lot of small aircraft engines weigh around 150kg and several use gear boxes as well.

So Does this mean you could save the weight to make the plane electric but not battery powered or is the generator simply going to be too inefficient?

https://www.google.com/amp/s/settysoutham.wordpress.com/2010/05/26/portable-generators-about-half-as-efficient-as-power-plants/amp/

I know a lot of small aircraft engines weigh around 150kg and several
  use gear boxes as well.

Almost no piston aircraft use gearboxes. The only one that I know of that ever did was the Porsche Powered Mooney PFM which was largely a failure overall, with the gearbox being often cited as an issue. Smaller turbo-prop planes do use gearboxes due to the super high RPM range of a turbine but those are generally larger than the ones that seem to be in question here.

  So Does this mean you could save the weight to make the plane electric
  but not battery powered or is the generator simply going to be too
  inefficient?

As mentioned the issue here is simply weight and line loss. You are taking mechanical energy converting it to electrical, bussing it somewhere then converting it back to mechanical. There will always be line loss in a process like that when you don't really need it (since you need to spin the prop to begin with). Gas-Electric (be it diesel or gasoline) is advantageous as you can drive full torque at 0-RPM which is useful when getting a giant freight train rolling but does not provide a ton of benefit to light aircraft. You are also introducing at least 3 major points of failure (engine -> generator -> motor) to a system that previously only had one.


Why apply resolutons in data words for ARINC 429 bus Data words transported over the ARINC 429 bus are defined and built-in units, ranges, refresh rates, number of significant bits, and resolution.

Why is it necessary to include resolution? Does resolution really have any significant impact on the signal? I think resolution is just a mere step size for the signal, so why use incremental resolutions, like 0.0000000002? Does this small incremental really make a difference in the data word?

The ARINC 429 Word resolution tells you what value the LSB corresponds to. You can also tell what the resolution should be by looking at the Range and Significant Bits.

It doesn't describe the actual electrical signal.


Is there an audible warning on commercial aircraft if you try to land gear up? In one of the comments on this question (under the accepted answer), someone remarks that

  Aircraft can legally fly without a system to alert the crew when they are landing with gear up, etc.

Are these systems installed on commercial aircraft as a legal requirement?

All turbine-powered aircraft used in scheduled airline service under CFR Part 121 are required to have an approved TAWS installed;

  §121.354   Terrain awareness and warning system.

  (a) Airplanes manufactured after March 29, 2002. No person may operate
  a turbine- powered airplane unless that airplane is equipped with an
  approved terrain awareness and warning system that meets the
  requirements for Class A equipment in Technical Standard Order
  (TSO)-C151. The airplane must also include an approved terrain
  situational awareness display.

  (b) Airplanes manufactured on or before March 29, 2002. No person may
  operate a turbine-powered airplane after March 29, 2005, unless that
  airplane is equipped with an approved terrain awareness and warning
  system that meets the requirements for Class A equipment in Technical
  Standard Order (TSO)-C151. The airplane must also include an approved
  terrain situational awareness display.

  (c) Airplane Flight Manual. The Airplane Flight Manual shall contain
  appropriate procedures for—

  (1) The use of the terrain awareness and warning system; and

  (2) Proper flight crew reaction in response to the terrain awareness
  and warning system audio and visual warnings.

The TAWS system includes the functions of the older Ground Proximity Warning System (GPWS).

GPWS Mode 4, Flight Into Terrain with Less Than 500 Feet Terrain Clearance and Not in Landing Configuration, provides for alerts to the crew when entering a defined envelope below 500 feet (based on height and rate of descent) and the gear is not in landing configuration. There is also an alert envelope for Flaps not in landing Configuration.

The Mode 4 alert consists of an audible alert "TOO LOW, GEAR. TOO LOW, GEAR."


Re old (1992) US VFR sectional charts-- when was the thin dashed magenta line first used? When did the thin dashed magenta line, currently used to illustrate Class-E-to-surface airspace, first appear on the legend of US VFR sectional charts?  I'd like to narrow down the date as precisely as possible. Currently I'm aware that this marking DID appear on the legend of a sectional chart (Hawaiian Islands) effective November 12 1992, and did NOT appear on the legend of a sectional chart (Bethel Alaska) effective August 20 1992.  Please post the "effective date" of any US VFR sectional chart that you are aware of before November 12 1992 in which the thin dashed magenta line does appear on the legend, or the "effective date" of any US VFR sectional chart that you aware of after August 20 1992 in which the thin magenta line does not appear on the legend.

Note that on the legend of the November 12 1992 chart, the thin dashed magenta line is identified not as depicting "Class E airspace", but rather as depicting "Control Zone at airport without control tower and Control Zone extension without communications requirement".  The term "Class E" didn't show up on legend of US VFR sectional charts until 1993.

The decision to change the airspace classification in the US to bring it into agreement with ICAO classifications was made in December 1991, as can be seen in the US Library of Congress:  Federal Register: 56 Fed. Reg. 65415 (Dec. 17, 1991).

The ICAO classification was only used from the 16th of September 1993, but as part of the familiarisation process for pilots, the legends of the charts were already updated before.

The Federal Register (FR) contains a table with the Airspace Reclassification Transition timeline.

This table shows that as of October 15, 1992, the first sectional aeronautical charts (SAC), world aeronautical charts (WAC) and terminal aeronautical charts (TAC) are published with legends that indicate both existing and future airspace classifications.

Furthermore the FR specifies that it is anticipated that a segmented magenta line will be used for class E in the future, and that starting October 15, 1992, the new colours will be used in the legends.

  An anticipated modification to the symbols on aeronautical charts is
  the addition of a segmented magenta line to represent the controlled
  airspace area for airports without operating control towers that
  extends upward from the surface (Class E airspace).

  [....]

  The legends in aeronautical charts
  will include both the existing airspace
  classifications and the airspace
  classifications to be effective September
  16, 1993. For example, the solid blue line
  that symbolizes a TCA will be followed
  by "TCA (Class B)." The first charts
  with a dual legend will be published
  October 15, 1992. Commencing
  September 18, 1993, the legends on these
  charts will be reversed (e.g., a solid blue
  line will be followed by "Class B
  (TCA)". Between March 3 and August
  17, 1994, the use of dual indication
  legends will be phased out.


What are these three indentations on the SBD's wing? I was looking at pictures of WWII planes and noticed that the SBD Dauntless had 3 indentations towards the tip of the wing. What were these for?

According to "The Dauntless Dive Bomber of World War Two" by Barrett Tillman, they are "letter-box" anti-stall leading edge wing slots added to improve the planes stability when approaching the 78knot stall speed during landings (and take offs, actually.)

The initial versions tended to not be able to build up enough speed during the (catapult-less) take offs from the carriers of WW2, and would simply drop off the front edge of a carrier. Adding the three slots basically fixed (or lowered) the speed of stall.


Why don’t aircraft use run-flat tyres? Tyre failures on aircraft during takeoff are fairly common, and are usually (though not always) caused by flat or underinflated tyres (via the overdeflection and overheating experienced by tyres with abnormally low internal pressures).  If an aircraft tyre fails during takeoff, this is dangerous in several different ways:

Flying tyre fragments can damage other parts of the aircraft, as well as, potentially, other nearby aircraft or ground personnel.
Wheels with blown tyres are useless for braking, thus greatly increasing the chance of a runway overrun should it become necessary to reject the takeoff.
A tyre failure(s) can greatly degrade directional control, especially on smaller aircraft that only have a few wheels to begin with.
A failed tyre dragging on the runway can easily heat up enough to ignite and burn, dooming the aircraft if the crew then retract the landing gear without knowing that said landing gear is on fire.

Run-flat tyres are designed to remain useable even in the event of a total loss of internal pressure (generally by incorporating an internal weight-bearing skeleton inside the tyre’s air chamber); given the potentially catastrophic consequences of a flat tyre failing during takeoff, why don’t aircraft use run-flat tyres?

The same reasons that run-flat tires aren't more common on cars or trucks are amplified with aircraft.

They're more expensive and can wear out faster. They will also be much heavier. This has to be traded against the cost of an occasional flat tire.
They typically have a maximum speed when flat. Aircraft tires need to operate at much faster speeds than vehicle tires. Many of the examples you provided were made worse by under-inflated tires.
They typically have very limited range when running flat. Again, many of your examples involved under-inflated tires. If they left a regular tire to burst, the same would happen to a run-flat tire.
Many tire failures are due to the tires bursting, not just a simple puncture that makes them go flat. A run-flat design will not help in this case, and may even make the fragments more dangerous.

All of your airliner examples were on pretty old aircraft models, and many included additional factors. Regulations and procedures change over time in response to these sorts of accidents. When properly maintained and operated, aircraft are designed so that a disintegrating tire won't cause serious hazards.


Does the crew have a professionally mandated responsibility to inform passengers of a potentially fatal emergency? This follows on from the question here on an incident wherein a passenger asked crew about an aberrant situation during a flight.

Gathering from the answers to the question, flight crew's priority is to handle the emergency, and part of that is keeping passengers cooperative and calm, whether by informing them of details or perhaps omitting them in the interest of maintaining decorum.

However, in the case of a potentially fatal emergency, wherein passenger death is probable, despite the interest to maintain calm, does the crew have a professionally mandated responsibility to inform passengers? There are obviously moral and ethical motivations for this, but these might be beyond the scope of the site and as such I am asking how these issues are dealt with.

By "professionally mandated responsibility," it can be by laws in the appropriate jurisdiction, regulations and internal policies by the airline, common practice, or guidelines set by an aviation body.

Would the act of informing passengers they may die be considered "professional" or "a responsibility of the crew"? No.

And if I may argue, it's the opposite: it is unprofessional for trained flight crew (either pilot or cabin crew) to behave this way.

The shortfalls of this action is obvious. Panic would instantly spread among the cabin. Many people would start behaving irrationally when they believe that death is imminent (hey, not everybody is strong psychologically). This could potentially turn a survivable situation into a deadly one.

In dangerous scenarios, anyone assisting needs to give assertive instructions. We don't tell people why they are doing it. We give very simple, but firm instructions such as "push!", "jump!". Fire fighters and other rescue workers also do it this way.

Telling people "uhhhh, I don't think we can make it" works against the goal of ensuring everyone has a best chance of survival, which is a professional responsibility of any crew member on a passenger flight.

Legally, there are no regulations, industry practices, or airline SOP that I'm aware of, that mandates informing passengers about the potentially fatal outcome of their flight.

Realistically, there aren't that many scenarios where this is possible. If it's a small problem such as high oil temperature or failed hydraulic pump, you won't even notice. If it's a stall or loss of control you'd be screaming already. If it's a inflight breakup you'd loss consciousness in less than 30 seconds. If it's a cabin fire you'd see cabin crew fighting it with fire extinguishers.

That leaves scenarios where the aircraft is stable in the air, but may break up upon landing. Examples would include landing gear malfunctions, flap malfunctions (causing very high landing speed) and total engine failure from high altitude. Historically, most of these incidents end up well. Spending the time to educate passengers emergency procedures (such as counting the number of rows to various exits; briefing how to open the emergency door) is more constructive then saying "On behalf of XXX Airlines, it is with sincere regret to inform you that our aircraft suffered a catastrophic failure and this may be the last moments of your life".

That said, I offer the following:

If you've been told to adopt the brace position, you may consider that it is in the opinion of the flight crew that severe injury and/or death is likely.


What is the difference between Distant (D) NOTAMs, Local (L) NOTAMs and FDC NOTAMs in the US? I would like to know the difference between Distant (D) NOTAMs, Local (L) NOTAMs and FDC NOTAMs in the US. Is their meaning obsolete or still in use by the FAA?

Short answer: D NOTAMs are about airports and navigation facilities; FDC NOTAMs are about airspace, procedures or regulations; and L NOTAMs don't exist any more (unless you're in the military).

The information on NOTAM types is a bit messy and inconsistent, to say the least. The Alaskan FSS lists 11 types; the PHAK 13-3 lists 3 types (as acpilot mentioned in his answer); the AIM 5-1-3 lists five in its NOTAM section, plus GPS NOTAMs in the GPS section.

And the FAA's military NOTAM site lists yet more types in their FAQ  such as M, V, W and F.

Anyway, here's what the AIM says about D and FDC NOTAMs:

  NOTAM (D) information is disseminated for all navigational facilities
  that are part of the National Airspace System (NAS), all public use
  airports, seaplane bases, and heliports listed in the Chart Supplement
  U.S. [...]  NOTAM (D) information includes such data as taxiway
  closures, personnel and equipment near or crossing runways, and
  airport lighting aids that do not affect instrument approach criteria,
  such as VASI.

  [...]

  FDC NOTAMs. On those occasions when it becomes necessary to
  disseminate information which is regulatory in nature, the National
  Flight Data Center (NFDC), in Washington, DC, will issue an FDC NOTAM.
  FDC NOTAMs contain such things as amendments to published IAPs and
  other current aeronautical charts. They are also used to advertise
  temporary flight restrictions caused by such things as natural
  disasters or large-scale public events that may generate a congestion
  of air traffic over a site.

According to the Alaska FSS page, NOTAM(L) doesn't exist any more for civilian use:

  NOTAM (L):  A NOTAM given local dissemination by voice and other
  means, such as telautograph and telephone, to satisfy local user
  requirements.  This type of NOTAM is now used only in the military
  NOTAM system.  All NOTAMs previously considered NOTAM (L)s in the
  civil NOTAM system are now considered NOTAM (D)s.

That's confirmed by AIR FORCE INSTRUCTION 11-208 (I), which describes NOTAM(L) as a military type:

  4.2.1. Military.
  [...]
  4.2.1.2. Local NOTAM (L series). Local NOTAMs are non-critical and non-safety related information that is essential for the flying and
  support communities to know. Facility managers may establish the
  parameters for local NOTAM determination.

Civilian L NOTAMs are now D NOTAMs that start with the specific facility code. You can find them on the civilian NOTAM site, e.g.:

  !LOU 05/077 LOU RWY 15/33 CLSD
  1605091213-1606222000

And to address your final point, NOTAMs are not obsolete. There needs to be some way to inform pilots about temporary changes or things that happen at short notice, and that's what NOTAMs are for. Many people feel that the system could be improved somehow - pulling up the NOTAMs for even a short flight can give you dozens of results - but there's no doubt that it's needed. Reviewing NOTAMs is an important preflight step, and examiners often test you on it during checkrides. There are plenty of NTSB accident reports that mention NOTAMs, usually in cases where the pilot didn't review them.


If all control surfaces were disabled, could a passenger plane be controlled by distribution of the passengers? Let's assume that a large military plane has its control surfaces disabled in combat. The engine(s) can still be controlled. There is a substantial number of ground forces being transported.

In theory could the plane be flown purely by distribution and redistribution of the weight of the passengers? Note these are military personnel and are used to acting on orders.

There are different degrees of control. The plane could at least be made to crash in a different debris pattern than if the input was not made, and even that's a form of control.

As the whether the plane could be controlled enough to land, and do so, as the question states, with all of its control surfaces disabled, let's see. You get considerably pitch control authority, with poor speed and accuracy, but very little direct roll control. Differential thrust provides a decent amount of yaw control.

So the first question is: Is the plane already on the glideslope of a straight-in approach to an airstrip? If yes, then passenger movement should, with some luck, suffice to get the plane down to the ground.

If not, getting a plane to a suitable landing spot becomes more difficult. Many military transports are designed for rough field landing, so over flat and easy terrain, it should be possible to get some sort of landing that is better than an uncontrolled crash. If the terrain is not so forgiving, it comes down to trying to navigate and fly with greatly reduced control responsiveness and precision, where many inputs will be made wrong, and down to whether they can be corrected in time.

To make an analogy, if a driver transporting a blind passenger falls out of the car, can it be controlled from the back seat by moving controls with the passenger's walking stick, acting on advice shouted from cars passing by? That's how trying to fly a plane that way would probably feel.

That said, much stranger things have happened. People have fallen out of airplanes without parachutes and survived. Planes have landed themselves smoothly after the pilot has ejected. And landings with a loss of most controls have happened as well.


What's the minimum timeline for fixing the issues/finding from NTSB/FAR? When air-crash investigation completes, either NTSB/FAR/other investigating agency finds some issue with instruments/equipments. What is the minimum timeline given to instrument/equipment manufacturer to fix the issue? (May be based on the severity of the issue).

That is up to the civil aviation authority, which in most countries is distinct agency from the investigation board (in USA this is FAA), to decide.

They will take into consideration how likely the problem is to repeat, how big risk it would be if it does¹ and as secondary criteria how much work the fix is and how much it will cost. What must be done will be published in an airworthiness directive.

If the problem is serious, they will prohibit any further flights except for testing purposes until fix is installed. And remember the fix may not be known yet. For example after the 787 battery fires, FAA published airworthiness directive that prohibited operations until “approved fix is installed” couple of days after the third incident when they just started to discuss what the fix should be with Boeing and whole fleet remained grounded for almost half a year until the modified batteries were ready.

On the other end of the scale a problem may not necessarily result in mandatory change at all. Many issues simply result in mandating additional inspections, shortening intervals between inspections or shortening maximum service life of some component, which may be relaxed again if the manufacturer develops an improved version of the component and the operator installs it, neither of which is mandatory. Even quite severe problems may just be solved with inspections, because most components have inherently limited life and the problem just indicated higher wear then originally anticipated.

¹ It is important to remember that the investigators don't only investigate crashes, but they get reports of all incidents, which means any failure where there was elevated risk. They then investigate those where they consider the risk significant or that are more common then expected. So often things are investigated where the probability of fatal outcome is low. In such cases the investigators will only consider safety and will publish a safety recommendation, but the aviation authority has to also consider other practical aspects and may choose not to enforce it.


Is it normal to take off with limited flaps on a B737? Is it safe/normal to take off (fully loaded from Cyprus to Kenya - 6 hours) with very small flaps extended? Model of aircraft: Boeing 737-800. He used whole length of the airfield to take off, the next acceleration took a long time at low level, and the next climb happened very slowly.

That looks like Flaps 1, and that is not only normal and safe, it is very common on relatively long runways (7500' and longer). For slightly shorter runways, a Flaps 5 takeoff is often used, and for the shortest runways (less than 5500', roughly), even Flaps 15 or on some aircraft, Flaps 25.

All of those are entirely safe options.

As the runway gets shorter, you get the best performance -- defined as how much weight you can carry while still meeting all requirements -- with an earlier liftoff. This means, more flaps to enable rotating at a slower speed. The downside of more flaps is more drag, which reduces initial climb performance. To get the most weight possible, you'd use an extremely long runway, a high takeoff speed, and minimal flaps (i.e. Flaps 1 as you had) for the best performance in the climb. But when the runway isn't so long, you start to be more limited in the weight you can carry, and to get the best results, more & more flaps become optimal as the runway gets shorter.

It sounds like your flight was probably pretty heavy -- a full -800 certainly would qualify -- and so the crew took advantage of the long runway to accelerate to a fast takeoff speed using Flaps 1. In the air, the aircraft will fly fine at that weight, but it isn't as nimble and won't accelerate as quickly as a lighter 737 would. If you're used to the performance of a 737 loaded with the fuel for a one or two hour flight, it isn't surprising that the aircraft with enough fuel for a 6 hour flight (plus reserves, in both cases) would seem sluggish in comparison.


What technical problems stopped scramjets from being used on hypersonic aircraft? I have been researching hypersonic aircraft and scramjet engines after running a few calculations looking at ramjet/rocket hybrids for making single stage to orbit vehicles. After doing the analysis and reading a little bit of the development history, I am still a little baffled as to what stopped the development of the engines to get deployed on aircraft and rocket.

What is keeping the engine cool enough to not melt or fly apart at design speeds? Was it making sure the inlet compressed the air quickly enough without slowing the flow with a normal shock? Was it making sure the structure of the engine was light enough to still produce enough thrust to fly the aircraft?

If these were the problems, why were they hard to solve? Was it that we did not know how to get enough cooling for low pressure drop? Or know how to locate shockwaves in the intake because the ratio of specific heats changes?

I'm don't research hypersonic flight, but I bet the primary barriers of hypersonic flight are less technological and more political/economical. After all, we pay money and conduct research in order to solve technological problems.

You would think that developing an engine is primarily a task for aerodynamicists since they can design better intakes, compressors, nozzles, etc. However, materials science will typically limit what an engine manufacturer can actually build as you mentioned in your question. Let's imagine aerodynamicists design can design a scramjet that can reliably run for a thousand cycles, but the engine is useless if the aircraft's skin can't handle the high speeds.

More importantly, who's willing to pay for super-inefficient scramjets? Commercial airliners (consumers) weren't even willing to pay for the supersonic Concorde, so you can easily discount them from buying scramjet-powered aircraft. That leaves the military. In the 60s, the military was willing to pay for speed (see SR-71, XB-70), but then stealth became more attractive than speed and super/hyper-sonic research fell by the wayside.

Now the US, China, and Russia are again funding hypersonics research in part because stealth is losing its advantage. Moreover, some startups (Aerion?) are exploring supersonic business jets for the really rich folks, so you're starting to see their engineers exploring hitherto exotic supersonic tech. However, hypersonic flight will still be beyond the means of an average consumer.

TL;DR: Hypersonic research probably stopped less because of tech problems and more because stealth offered more bang for the military's buck. Now the pendulum is swinging the other way. Military supersonic technology is also making its way into the commercial sector for the uber rich.


What is this propeller found underwater in the English Channel? I need some help identifying this piece.

My best guess is that propeller is related to the 19 June 1954 – Swissair Convair CV-240 flight which was ditched in the English Channel near Folkestone due to fuel exhaustion. As @AEhere mentioned earlier it looks like the propeller wasn't under power.
the propeller shape look similar but still the size of the propeller being provided in the photo relatively small compared to the actual aircraft propeller.

Sources :

Wikipedia:https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_airliners_in_the_United_Kingdom

http://www.sr692.com/fleet/15_cv240/index.html


Do fly-by-wire flight controls in airliners provide artificial feel? Mechanical and hydro-mechanical flight control systems (cables, pushrods, hydraulics) all offer pilots some form of feedback – direct or, in the case of hydraulics, artificial – as the aircraft maneuvers and forces are applied to the controls.  I know that early FBW, like that in the F-16 prototypes, used a rigid system that often allowed pilots to over-control the aircraft.

Do fly-by-wire-equipped airliners, like their non-FBW siblings, use an artificial feel system to provide control feedback?

After some digging, I found an answer for myself: yes, some FBW airliners use artificial feel systems, but not all of them. According to Electronics in the Evolution of Flight (Google Books),

  The [Boeing] 777 fly-by-wire system employs envelope protection. This feature of the artificial-feel system provides increasingly greater force when the aircraft is pushed to its limits.

Conversely, Airbus does not provide any feedback to the pilots as their flight control system enforces control laws that cannot be overridden by inputs (source: Aerospatiale engineering document):

  The positioning of the control surfaces is no longer a simple reflection of the pilot’s control inputs and conversely, the natural aerodynamic characteristics of the aircraft are not fed back directly to the pilot.

Getting regulatory, since I did some further research: 14 CFR 29.395, certification of Transport Category aircraft, only states that the controls are required to resist a certain amount of force (i.e., not break). This differs from how much force is required to "achieve the positive limit maneuvering load factor" or otherwise impart changes to the aircraft's orientation (14 CFR 23.155 / 23.157).


In an F-18, how do rudders deflect during cross winds and gusts? Can rudders be deflected by different angles? Deflection of rudders can balance moment about the centre of gravity. I have thought of non-symmetric deflection of rudders so that net sideward force is create to balance the moment about the center of gravity of the aircraft.

The Hornet has a fly-by-wire flight control system that is run by 2 flight control computers (also known as Roll Pitch Yaw computers) and these each have 2 channels. This system gets pilot input from the controls but the computers will decide the most efficient way to impart the command signal using all of the available control surfaces. Pilot has no say in which surface moves. If they did, this aircraft would be a nightmare to control because, like most modern fighter jets, it has been designed to be inherently unstable. This allows it to be highly manoeuvrable during a dogfight.

Some of the surfaces are controlled by 2 channels (rudder, aileron, leading edge flaps). Some are quad redundant, utilising all 4 channels (Trailing Edge Flaps, Horizontal Stabs).

All of the surfaces, with the exception of the leading edge flaps from memory (because they are connected mechanically with a rod???), can deflect independently of each other, if the software/flight envelope permits. For example, if you want to roll a Hornet, some combination of all or some of the following surfaces may deflect: L and R Aileron, L and R Trailing Edge Flaps, L and R Horizontal Stabilisers. There are various sensors such as accelerometers which provide the negative feedback loop required to ensure the aircraft is getting to the required attitude at the expected rate. If it isn't, surfaces may deflect more or others may be commanded to help out. The circuitry inside the computer is basically a summing amp with the following inputs: command signal from the pilot, the position feedback from the surface and the rate feedback from the accelerometers. I think the important thing to understand is that this signal is nulled (0 volts) when the aircraft is pointing in the commanded attitude. That means no more movement of the surface.

With regards to rudder on takeoff, these accelerometers would sense an uncommanded change in the yaw axis and I suspect the flight control computers would damp this affect using the feedback method described above without the pilot really noticing much, certainly not having to stomp on a rudder pedal to compensate. There would be some sort of signal processing delay and mechanical reactive delay to correct the movement but this is all done without pilot input.

The rudders don't have to deflect symmetrically as they are controlled by different flight control computer channel pairs, one from each computer for redundancy. In fact, when the rudder fails, it is commanded to streamline and the other surfaces will compensate. The software programming inside the flight control computers that determines which surface/surfaces move and by how much.


What is the ratio between time in the air and time on ground for an aircraft? I suppose it may be different from an airline to another.
Given the maintenance, the time to load/unload the aircraft, the time the aircraft is grounded because there is no flight scheduled (e.g. at night), how many time an aircraft actually spend on ground compared to the time it spend in the air?

It will vary widely from aircraft to aircraft, but I will try to give some general estimates.

Time on the Ground

Part of what you are referring to what is sometimes called aircraft turn time. It's not really directly related to my calculations for your overall question (though it is certainly a factor for short-haul jets), but in this article, minimum turn times for the Boeing 757 was studied, and it was found that the estimated turn time for a 757-200 was 52.5 minutes, based on actual operations. The 757-300, a stretched model with more seating, would take about 59 minutes.

From this presentation, presented by United Airlines, they show a general guideline MSGT (Minimum Scheduled Ground Time), that is a generalization depending on flight locations, field facilities, and airlines. Some times are:

Boeing 747: 80 minutes
Boeing 777: 70 minutes
Boeing 767: 60 minutes (-300 model)
Boeing 737: 35 minutes (-300 model)
Airbus A320: 40 minutes

This link has a discussion of a number of airliner turn times, however none are from official sources. Most vary between 20-45 minutes, depending on if cleaning is required.

So for a typical airliner we can say it takes about 45 minutes-1 hour for a typical servicing.

Aircraft Lifetime

Now as to how many times they fly, you can find their aircraft design cycle limit (essentially, how many takeoffs and landings it can make in its lifetime) in this Federal Register document (summarized here). Some listed numbers:

Boeing 747: 20,000 cycles
Boeing 777: 40,000 cycles
Boeing 767: 50,000 cycles
Airbus A320: 48,000 cycles (60,000 hours)
Airbus A300: 40,000 cycles

So for a 'typical' airliner we can say it can survive about 40,000 cycles in a lifetime

You can find the average age of airliners in different places online. This site splits up by airline and aircraft, and most airliners have an average age of 12-15 years. But note that this is the active fleet. The average age at retirement for an airliner is now around 24-25 years.

You can find a related Aviation.SE question here

Aircraft Usage

This thread discusses the average cycles and flight hours per day. Long haul aircraft (like the 747, 777, A380) tend to spend more hours in the air per flight, but also have less cycles per day. I can't find official sources, but the thread presents a couple example averages for peak usage rate:

Delta Boeing 757: 9.5 hours/4.8 cycles
United Boeing 747: 13.2 hours/1.6 cycles

(I find these probably accurate, as there have been some publicized accidents that have much higher usage, like this one, which flew 48,740 hours and 39,781 cycles in 15 years - about 7 flights/day; short-haul jets like the one in the article end up with more cycles than long-haul, as I noted above).

It is difficult to find hard numbers, but overall, the average flight length for a short-haul jet is about 2 hours, whereas a long-haul jetliner is around 6-7 hours.

Again, there are a lot of variables in this question, but using the above data, we can estimate the answer to your question, using these estimated figures from above:

40,000 cycles (~20,000 flights)
25 years
2 hours/flight

This means approximately 40,000 flight hours for a typical short-haul jet; over 25 years (219,000 hours), this works out to about 1 hour in flight for every 5 on the ground. Obviously this varies widely, but for a ballpark number, that's the best I can do. The highest usage would be a heavily used long-haul jet used on the longest routes from a busy airline (i.e. trans-Pacific; Middle East to U.S.), whereas the lowest would be a moderate-length flight on a low-volume route. In general, you are probably looking at about 1:3 to 1:5 air:ground time.


Why did Concorde have a 8000 ft airport elevation limit? According to the Concorde Flying Manual Volume II(a) - 1 Operating Limitations - page 01.01.02 the take-off and landing airfield altitude is minimum -1000 ft and maximum 8000 ft. Why is Concorde limited to a maximum airfield altitude of 8000 ft, excluding Concorde from airfields like El Alto International at 13,323 ft?

My initial thoughts were either maximum braking action limitations for rejected take-off or maximum tire speeds, but unfortunately the manuals linked above do not mention max tire speed or brake energy limits.
Update: As @gwally pointed out, Concorde did fly to Bogotá, Colombia with an airfield elevation of 8363 ft two times, in 1974 and 1975. So it seems the 8000 ft maximum airfield elevation seem to be a certification limit or operational limit, and not a performance limit of Concorde.

Edit: Concorde can take off and land above 8,000 ft
From October 20-28, 1974, Concorde 02 (F-WTSA) made a tour of the American Pacific coast, visiting London (83 ft), Gander (495 ft), Mexico City (7,316 ft), San Francisco (13 ft), Anchorage (151 ft), Los Angeles (125 ft), Lima (112 ft), Bogotá (8,710 ft), Caracas (236 ft), Las Palmas (78 ft) and Paris (392 ft).

http://www.concordesst.com/history/70s.html

El Dorado International Airport - BOG (Bogotá) has an elevation of 8,710 ft (2,648 m), which puts in 710 feet above the limit of the 8,000 ft maximum altitude. Both runways are 12,467 ft (3,800 m), so capable of handling a take-off.
In addition, Air France flew Concorde twice weekly to Mexico City's Benito Juárez International Airport - MEX (Elevation AMSL 7,316 ft / 2,230 m) via Washington, DC, or New York City, from September 1978 to November 1982.http://www.concordesst.com/history/70s.html
This shows that Concorde was able to schedule regular service to an airport 684 ft lower than the 8,000 ft maximum altitude and visit an airport above 8,000 ft.
I am not sure the 8,000 ft is a hard maximum elevation. It could be for a fully loaded plane. I have not seen any chart to show maximum take-off weight at any altitude.


Do aircraft use the same or similar warning alarms for different alarm conditions? I was going through Helios crash and learned that Boeing was blamed for having similar sounding alarms for different alarm conditions.

On a given aircraft, can two different warning alarms have the same sound?
If so, what other aircraft have the same sound for different kinds of alarms?
Has Boeing changed their alarm systems post that incident?

Has boeing changed their alarm systems post that incident?

The story of Helios Airways flight 522 is complicated. It is not clear that a misidentified alarm was the cause of the crash.

Update:

If you are talking about the cabin altitude warning horn, that was allegedly misidentified as a take-off configuration, then nothing has been changed, at least up to May 2015 (see: The Boeing 737 Technical Guide, Version 70, May 2015, bottom of the page 50).

  "As the aircraft climbed, the pressure inside the cabin gradually decreased. As it passed through an altitude of 12,040 feet (3,670 m), the cabin altitude warning horn sounded. The warning should have prompted the crew to stop climbing, but it was misidentified by the crew as a take-off configuration warning, which signals that the aircraft is not ready for take-off, and can only sound on the ground.
  In the next few minutes, several warning lights on the overhead panel in the cockpit illuminated. One or both of the equipment cooling warning lights came on to indicate low airflow through the cooling fans (a result of the decreased air density), accompanied by the master caution light. The passenger oxygen light illuminated when, at an altitude of approximately 18,000 feet (5,500 m), the oxygen masks in the passenger cabin automatically deployed."m, Source: Helios Airways Flight 522.


Can a Diesel Aircraft engine be run on Car Diesel? What are the operational differences between normal diesel fuel used in cars and the Jet-A diesel type fuel used for some prop aircraft such as the Diamond DA62? I know that aircraft use Jet-A fuel, but could an airplane be run on car diesel?

In at least some cases, yes. Continental's CD-155 diesel engine will run on auto diesel, Jet A or any mixture of both:

  The CD-155 is certified for the use of both jet fuel and diesel (DIN
  EN590) and is running with the two fuels in any mixture ratio.

EN590 is the European standard for auto diesel. The Gemini 125 engine can run on Jet A and diesel according to their website, as can the Austro AE300. So it seems that in general, aircraft diesel engines can indeed run on auto diesel.


Why is the FOV of the Synthetic Vision of the Prodigy Flight Deck asymmetric? Why is the FOV of the Synthetic Vision of the Prodigy Flight Deck asymmetric?

I am just reading through the manual of the Prodigy® Flight Deck 100 and came to the chapter about the synthetic vision. The document states:

  [...] The field of view is 30 degrees to the left and 35 degrees to the right. [...]

Source (Page 510)

What is the reason and what are the advantages of having such a FOV with 30° to the left and 35° to the right?

According to the FAA's AC 25-11B, there is no requirement for the asymmetrical SVS field-of-view.

It's not a feature either, as in there is no benefit. Whereas an Enhanced Vision System (EVS) system benefits from an offset overlay to match the sensor's deviation to the different flight deck seat positions.

With that said, here's my guess on why it sees 5° more on the right side.

From the FAA AC linked above:

  The display can depict the scene from the pilot’s view looking through the front window (egocentric) or from outside the aircraft (exocentric). However, if implemented on a primary display, then the display must depict the scene from the pilot’s perspective looking through the front window.

This means the SVS is egocentric, which leads me to conclude* that the left seat is more-or-less aligned with the attitude indicator's centerline. But because of the display's size, the attitude indicator itself is off center, resulting in the bigger angle (5° in this case) to the right.

Which would explain the equal distances shown in white below. They could have been adjusted to allow a centered attitude indicator with the altitude tape being wider than the speed tape.

(Source; added arrows)

* My conclusion is based on the assumption they would want the SVS graphics to share the center of rotation of the attitude indicator. This poses a question with regard to the right seat, because as I can see from this image, the seating position is not accounted for (unlike with EVS).

But since SVS is not meant for barnstorming, I just might be overthinking it. Also, SVS does not need to show everything:

  SV depictions on the PFD have the potential to provide pilots with enhanced terrain and landmark awareness during non-precision and precision approaches. However, the display may not provide depth perception and may not provide a field-of-view for pilots to know what is to the left and right of the display view area.


What is the purpose of wide area multilateration? From what I understand the wide area multilateration (WAM) technique is similar to Loran-C but reversed:

The aircraft ADS-B transponder broadcasts a signal received by several ground stations.
The differences in time of reception draw hyperboloids of revolution in space, their intersection is the aircraft position.

Multilateration principle

What are the intended uses of this inexpensive system which seems redundant with ABS-B, GNSS and SSR? Are aircraft in the world already using WAM? Is multilateration intended to replace other system(s)?

Wide Area Multilateration (WAM) is used as an ATC surveillance system. Like Secondary Surveillance Radar (SSR) it is classified as a cooperative independent surveillance system; the aircraft has to cooperate (i.e. an active transponder) but position is determined independent from data sent from the aircraft (unlike e.g. ADS-B).

A WAM system relies on Time Difference of Arrival (TDoA) measurements to determine the position of aircraft. At least 4 receivers with synchronised timing are needed to calculate the position of a transmitted signal. In practice WAM systems have a redundancy built in to them and are operated with more than 4 receivers. It can operate purely passively but usually the system will interrogate aircraft transponders to ensure a sufficient update rate can be maintained. This is a downside of the system; with its omnidirectional interrogators it is often considered as using much capacity on 1030 MHz, causing an increased transponder load (every incoming interrogation needs to be processed by a transponder, even if it is intended for another aircraft and no reply is to be given).

The system is used as an alternative to secondary radar. The installation of a receiver is much cheaper than a radar, but the life cycle cost of the surveillance system depends also on site renting costs, communication costs and maintenance cost. Maintenance tends to be cheaper (no rotating radar head), but communication is more expensive (more lines). Overall, WAM is a cost effective alternative to SSR.

WAM is able to achieve very high accuracy and high update rates when a sufficient number of sensors are installed. For example, German Air Traffic control DFS operates the Precise Approach Monitoring system in the Frankfurt TMA with 36 receivers and achieves and accuracy better than 25 meters with an update rate of 1 second.

In mountainous terrain, valleys can be covered by installing receivers on mountain peaks, which is much cheaper than covering it all by radars. Austrian Air Traffic Control AUSTROCONTROL operates a nationwide system consisting of 60 receivers.

In terrain that is difficult to access for maintenance or where there is no infrastructure to install radars WAM may also provide a solution. On the North Sea both Dutch (LVNL) and British (NATS) Air Traffic Control operate WAM systems to provide air taffic surveillance services to helicopters operating on the oil platforms. Receivers are installed on oil platforms.

WAM is used around the world, other deployments include for example Afganistan, Australia, Denmark, Ghana, Namibia, USA and many more.

The system can at the same time provide an ADS-B data stream from received ADS-B messages and can add extra security checks by comparing measurements of the data sources.


Does turbulent flow encourage/avert flow separation? I know that turbulent flow has more energy than laminar flow and hence can sustain adverse pressure gradient for a longer period of time. It basically delays flows separation.

But referring to this source from aviationchief.com, turbulent flow encourages flow separation.
I'm not exactly sure whether statement is true so can anyone give me an explanation behind this concept

This is what I think - Since turbulent flow is known for having skin friction drag, it slows down air after the suction peak. This slow down of air (due to pressure rise and skin friction caused due to turbulent flow) is gonna cause flow separation.

Turbulence delays flow separation. This is why we attempt vortex generators and turbulators in aerodynamic design when local flow separation is an issue.

A. Adverse Pressure Gradient

Fundamental to the generation of subsonic lift, as airflow accelerates over the leading edge, its pressure drops, resulting in net suction. At some point, usually corresponding to the point of re-converging airfoil geometry, the flow begins to decelerate as its pressure rises, eventually equating to the flow pressure on the lower surface at the trailing edge. This process is called pressure recovery, and the increasing pressure profile along the upper surface is called adverse pressure gradient.

Image modified from: https://conself.com/blog/calculate-lift-drag-with-paraview/

B. Laminar Boundary Layer

Within the boundary layer, which is a thin envelope flow close to the airfoil surface, an adverse pressure gradient in the external flow can slow the flow close to the surface (which is already much slower than the external flow due to no-slip condition) to a standstill. At that point, the separation occurs. This is more or less the story with laminar boundary layer where the flow is smooth.

Image ref: https://en.wikipedia.org/wiki/Flow_separation#/media/File:Boundary_layer_separation.svg

C. Turbulent Boundary Layer

Now in the case of a turbulent boundary layer, there is a lot more mixing going on within the boundary layer due to eddies. As a result, there is continued energy injection into the bottom layer flows, which delays the flow separation that would normally occur in a laminar boundary layer.

Image ref: http://www.bakker.org/dartmouth06/engs150/11-bl.pdf


What are the consequences of disobeying cabin crew during emergency? I was wondering what would be the consequences of disobeying flight crew due to emergency.

I was watching a video of Singapore B773 enroute on Jun 27th 2016 that landed, had a wing on fire, and passengers were made to sit and wait with the plane on fire. I would find it very hard not to attempt to evacuate plane.

There are laws which mean you must comply with crew orders at any time whilst on an aircraft. This is especially important in an emergency. In the Singapore example, imagine if a passenger had, without thinking (as tends to happen in emergencies), opened up a door on the side that was on fire. Fire could have entered the cabin, ensuring fatalities.

However, no prosecutor is going to pursue charges against someone for disobeying directions in an emergency, unless their actions clearly led to serious harm. Every evacuation, so many people stop and try to get their carry-on items, when they are clearly told not to. Even though this increases the chances of other people dying, nobody has been prosecuted for that (to the best of my knowledge).


What's the reasoning for safety wire on aircraft, and the reasoning behind the way it's routed? I'm assuming saftey wire is used near propeller assemblies where a lot of vibration occurs, or where the different speeds and altitudes aircraft are at could cause expansion or contraction based on temperature.  Is that correct?

I'm also wondering the reasoning for routing them in this manner. Is it done this way to counter vibration so both bolts don't loosen? If one is going counter-clockwise due to vibration, I'm assuming it'd be tightening the other bolt or vice versa?

Safety wire (positive wire locking) is done in areas where there is a possibility of the bolt getting loose due to vibration (also in other critical areas); this is done in a way such that the loosening of the bolt is counteracted by the tension in the wire i.e. in case the bolts loosen, the locking wire becomes taut and prevents further movement of the bolt.

safety wire examples; image from www.stangtv.com

There are different ways of doing wire locking for locking depending on the number of fasteners involved, but the basics are the same.

Safety wires; image from FAA AC 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair


How do manufacturers/kit providers determine Vne? Vne defines the maximum indicated airspeed which should not be exceeded. And clearly, doing so would result in "bad things" happening like flutter, etc. Presumably manufacturers do some sort of design work to determine likely Vne but how do they test for that? Exceeding Vne would put the aircraft into a structural failure situation would it not?

$V_{ne}$ is typically set to about 90% of $V_D$, the maximum design dive speed.  This difference provides a safety margin.  Above $V_D$, damage may occur due to flutter or structural failure, or controllability considerations may make the aircraft unflyable.  The aircraft is not guaranteed to fall apart at $V_D$ due to additional structural and manufacturing margins.

During flight test, the aircraft is flown above $V_{ne}$, up to, or close to, $V_D$.  Appropriate safety precautions are taken, e.g. parachute.  Any failure below $V_D$ indicates a design or manufacturing issue that must be resolved prior to certification.

The limitation to flight below $V_{ne}$ (as opposed to $V_D$) during regular operations provides protection against airspeed measurement errors, pilot errors and some margin against structural degradation over the lifetime of the aircraft.


Why do most commercial aircraft have their fuselage over the wing, instead of under? Almost all commercial jets today seem to have the fuselage/cabin mounted above the wing, why is this? why isn't it mounted under the wing like some freight airplanes?

Examples of above and under?

The related post, What are the pros and cons of high-wing compared to low-wing design?, does not address the passenger airliner related aspects.

Large commercial aircraft have low wings to stow away their long landing gears. Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Stretching makes it possible to tailor one basic design to a wide range of sizes, lowering the price of a single aircraft.

Large high-wing aircraft with their low fuselage position are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible. The military doesn't mind and prefers the high-wing variety. That Lockheed likes to stretch their transports (C-130, C-141) anyway is the exception that proves the rule.

Only turboprop-powered civilian aircraft may have a high wing, so there is more space for the propellers and the landing gear can be made short and light. Still, both versions exist. And the ones where the engineers did not know how to attach a jet close to the wing.

Aerodynamically a mid-wing position would be best. This is used when the payload is compact and needs little space, or is hung externally. In bombers, in other words.

In terms of stability and control both configurations are equivalent.


What happens if a student busts Dallas Fort Worth bravo airspace? What would happen if a student busts a corner, exceeds the floor of Bravo airspace by 500 feet then descends after one minute?

The pilot is on the frequency of a Golf airport heading towards a Delta controlled airspace, both within the Bravo 30 nm veil.

Does the Bravo tower have a way of knowing the aircraft involved?

Just to make it perfectly clear:

If you accidentally enter a controlled airspace without clearance, as soon as you realise what has happened, the first thing you do is contact the responsible ATC unit! Period.

Panicking, initiating a rapid descend to leave the airspace or simply pretending it didn't happen is extremely bad airmanship, and will surely get you in trouble if you get caught. On the other hand, admitting you made an honest mistake and asking ATC what the best solution is might still get you in trouble in some countries, but it is definitely the safest solution for everyone.

Depending on the exact details of the airspace infringement, it may be extremely dangerous if you try to solve the problem on your own. By suddenly descending to leave the airspace, you risk colliding with traffic below you. If the airspace in question is of a military kind, turning a blind eye to your mistake and maintaining radio silence will potentially result in a visit from some aircraft with a lot more weapons than yours.

Anyone can get lost and make mistakes. If you do, ATC is there to help you - not to punish you for an honest mistake. Make use of that help!

As for procedures about which forms need to be filed after an incident like this, I will leave it to someone with knowledge about FAA specific procedures to answer.

You can read more about Airspace Infringements at SKYbrary.


Why are so many ATR involved in accidents in the past years`? I asked myself a question why are so many ATR involved in accidents in the past years?

ATR-72, 16 October 2013, Lao Airlines Flight 301
ATR-42, 19 October 2013, P2-PXY, Air Niugini
ATR-72, 23 July 2014, TransAsia Airways Flight 222
ATR-72, 02 February 2015, TransAsia Airways Flight 235
ATR-42, 16 August 2015, Trigana Air Service Flight 257

ATR-72, 16 October 2013, Lao Airlines Flight 301

  The probable cause of this accident were the sudden change of weather
  condition and the flight crew's failure to properly execute the
  published instrument approach, including the published missed approach
  procedure, which resulted in the aircraft impacting the terrain.

ATR-42, 19 October 2013, P2-PXY, Air Niugini

According to released information this cargo aircraft overran the runway after the crew aborted the take-off above Vr after experiencing pitch control problems. The final report of this accident is not yet published but a preliminary report is available.  The investigation focusses on the payload distribution which may have caused imbalance leading to the perceived control problems.

ATR-72, 23 July 2014, TransAsia Airways Flight 222

The aircraft crashed on final approach in low visibility conditions (800 meters). During the initial approach the crew had requested and ILS approach (precision approach) to runway 02 but then changed their minds and asked for a VOR approach (non-precision approach) to runway 20. During the approach, after deactivation of the autopilot, the aircraft deviated 340 meters to the left and the crew subsequently announced they were going around. Shortly afterwards the aircraft hit tree tops and impacted residential buildings.

The final report is expected in October 2015.

To me it seems the probable cause is the failure of the flight crew to properly execute the published instrument approach including the published missed approach procedure which resulted in the aircraft impacting the trees and buildings.

ATR-72, 02 February 2015, TransAsia Airways Flight 235

The investigation into this accident is still running, only some preliminary information has been published. Preliminary data indicates that about 36 seconds after takeoff the engine no.2 auto-feathered, about 46 seconds subsequent to auto-feather the engine no.1 was shut off by the crew, resulting in loss of all thrust. The aircraft subsequently descended, stalled and crashed into a river.

ATR-42, 16 August 2015, Trigana Air Service Flight 257

This accident occurred just a couple of days ago so there are few facts known yet and no preliminary findings are published. I will not speculate about the probable cause of this accident.

The common thread in the first four accidents seems to be the failure to comply with established procedures resulting in the loss of the aircraft.

In two cases (Lao Airlines Flight 301 and TransAsia Airways Flight 222) the flight crew flew a controllable aircraft into the ground.

In the case of the Air Niugini crash improper loading of the aircraft is likely to be the cause, resulting in the aircraft being not trimmed correctly for take-off.

The crash of TransAsia Airways Flight 235 is the only crash that involved an aircraft system malfunction (engine 2 failure). However, the ATR-72 can fly on a single engine so the failure itself should not have been fatal. The crew then shut down the other engine (number 1) which sealed the aircraft's fate. It is too early to conclude that the crew didn't follow the correct procedures here; for example there may have been ambiguous indications from the engine instruments that led them to believe that engine no. 1 had failed. However with the information currently available it seems that the crew did not follow the correct procedures for shutting down a failed engine.

The high number of crashes involving an ATR aircraft seems not to be related to the model itself, but to the safety culture and lack of training within a number of airlines operating the aircraft.


Is it legal to begin pilot training on a jet? Disregarding financial and difficulty concerns, would it be possible (legal) for someone to obtain a PPL license on a jet aircraft?

If it is possible, would there be any restrictions on the license on operating piston engine aircrafts?

EDIT: the linked question asks about EASA regulations. This question is about FAA regulations, thus, the answer in the linked question does not apply.

There is nothing in the US regulations and no references that I can find that prohibits a pilot from learning to fly in a jet aircraft.  There are multiple systems on a jet aircraft that are not found in small GA aircraft and the same systems are more complex.  A lot of professional pilots who fly the same jet for a career don't fully understand the different systems on their jet.

The issue isn't with the FAA though; it is with the instructor and insurance companies.

I certainly would not agree, as a CFII, to train a new student pilot in a jet.  I personally don't want to take on the liability for the payment I would receive for my services.

Most insurance companies will not ensure a student pilot to learn to fly in a jet.


By what scale is Latitude and longitude calculated on aircrafts? If we travel by 1 metre on any side how much of longitude and latitude changes?

Since the flight is travelling so fast latitude and longitude changes quickly so how do they calibrate it?

PS:Is there any formula related to this?

If we travel by 1 metre on any side how much of longitude and latitude changes?

It depends where you start. One nautical mile is defined as a minute (1/60 of a degree) of longitude at the equator. This is about the same as a minute of latitude at the equator, but because of the shape of the earth, it's not the same as a minute of longitude anywhere else: lines of longitude get closer together as you head north or south, and they all meet at the poles. If the earth were spherical, the lines of latitude would all be the same distance apart, but it's not quite: it's squashed flat, like an orange, so latitude lines get closer together as well, but never meet.

Because it's simple geometry, you could make a formula to tell you the length of a minute of latitude at any latitude, and another to tell you the length of a minute of longitude at any latitude, but we don't do this, and here's why.

Latitude and longitude are a good way to describe where you are, but not how you're travelling. Instead, you plan to fly a certain distance in a certain direction. You can tell the distance by multiplying your speed by the elapsed time, same as any other navigation.

You can measure your position with reference to fixed points. In visual navigation (in sight of land), you can use geographic landmarks: a particular town is ten miles to the north, or you're directly over a lake. You can also use radio navigation aids: fixed radio beacons which tell you where you are in relation to them. These work even in bad weather or if you're too high to see the ground, and even airlines navigate this way. You can plan a route flying from one landmark or beacon to the next, until you reach your destination, without even thinking about latitude and longitude. When you need to report your position, even in an emergency, you do this by reference to these landmarks or beacons.

If you ever do need to know your latitude and longitude, you can do this by referring to your chart. You find the beacon or landmarks that you're at, mark your position on the chart with reference to those, and read off the latitude and longitude. No need for any formulae, and the only thing you have to calibrate is your compass.


Do pilots have to consider unplanned delays for Part 135 duty time exceedance? When flying under Part 135, is it legal to takeoff knowing that you will exceed the allowable duty time due to an unplanned delay after the start of taxi?

135.267(d) says:

  Each assignment under paragraph (b) of this section must provide
  for at least 10 consecutive hours of rest during the 24-hour period
  that precedes the planned completion time of the assignment.

So if the determining factor is the planned completion time of the assignment, am I good if my passengers showed up late on an earlier leg, or if I have to wait at the runway for 30 minutes before I takeoff if it will cause me to exceed the limit?

Note that if you operate under §135.267(b), that there isn't any specific duty time definition -- there are only regulations concerning the maximum flight time and minimum rest time in §135.267(d) (see this question for the definition of rest time). In a FAA Civil Penalty Order, it is noted that duty time is:

  any time that is not a rest period.

If you're operating under §135.267(c), "a regularly assigned duty period" is also not defined, however, a legal interpretation in 2009 states that:

  a pilot under a regularly assigned duty period "comes to work and ... goes home at the same time every day".

Now the question is, whether late passengers or being held up by ATC would be considered as affecting "the planned completion time of the assignment". The FAA has held in prior legal interpretations that:

  delays caused by late passenger or cargo arrivals, maintenance
  difficulties, and adverse weather are beyond the control of the
  certificate holder.

And in another legal interpretation:

  delays due to air traffic control, mechanical problems, or adverse
  weather could constitute circumstances that are beyond the control of
  the certificate holder.

However, it is noted that these provisions only apply if the original schedule was realistic. For example, if it is typical that ATC will place aircraft into a hold for 1 hour and this is not taken into account, this could be considered an "unrealistic" schedule for the purposes of §135.267.

Note that if no initial "planned completion time of the assignment" was calculated prior to accepting an assignment though, then "being late" may not be a legal defence if taken to court. In 1995, a case involving Charter Airlines, Walker and Mort questioned whether it was a violation of §135.267(b) & §135.267(d) to accept a flight even when it was known that the cargo would be late to arrive.

Because it was found that there was no "planned completion time of the assignment", they were on duty when waiting for the cargo (and therefore not "free of all obligations") and they had accepted the assignment after it was aware that the incoming cargo would be late, the FAA issued civil penalties amounting to \$10000 for Charter Airlines, and \$2000 each for Walker and Mort.


How should operations be conducted at a towered airport that is in uncontrolled airspace? How should operations be conducted at an airport with an operating control tower that is in Class E (controlled) or Class G (uncontrolled) airspace? Is this topic covered in an FAA publication such as the Aeronautical Information Manual (AIM) or Pilot's Handbook of Aeronautical Knowledge (PHAC)?

Airport with an operating control tower = talk to it.

From the regulations:

§91.126(d) (concerns Class G) and §91.127(c) (concerns Class E) are identical.

  Communications with control towers. Unless otherwise authorized or required by ATC, no person may operate an aircraft to, from, through, or on an airport having an operational control tower unless two-way radio communications are maintained between that aircraft and the control tower. Communications must be established prior to 4 nautical miles from the airport, up to and including 2,500 feet AGL. However, if the aircraft radio fails in flight, the pilot in command may operate that aircraft and land if weather conditions are at or above basic VFR weather minimums, visual contact with the tower is maintained, and a clearance to land is received. If the aircraft radio fails while in flight under IFR, the pilot must comply with §91.185.


Which jet airliner types have had the fewest accidents per million departures? Passenger jet transport is very safe, but are there any jet airliners with a lower recorded accident rate?

Edit:

number of accidents per se is of course never a good indicator since it will always rise over the years and with fleet size. Accidents per flying hour skews towards long distance aircraft, since not many accidents happen during cruise. The most objective comparison would be the rate of accidents per million departures of the type.

All newly developed types have zero number of accidents, at least immediately before the maiden flight.

Hence the actual safety of the type cannot be derived just from the number of the accidents. The number of flights flown must also be taken into consideration. For instance, Concorde used to be the absolutely safe (zero accidents) for many years (1969 - 2000), then it became comparable to other planes just because of the only crash of the type.

This source contains the table that includes the number of airliners operating, not just the number of accidents. It is very incomplete but looks like Boeing 777 and ERJ 135/145 may not be a bad choice while Boeing 737 'Classic' does not look equally good. The safety of this type has been discussed separately.


Which direction of a forward slip is safer during a turn to final? Suppose I'm making a turn from a left base to final and, realizing I need to kill quite a bit of excess altitude, decide to use a forward slip with full rudder deflection (along with full flaps).

Which direction of rudder deflection would be preferable?

I suppose that yawing left would result in less bank and therefore a lower load factor, which may be safe at low speed and low altitude. But yawing right, will result in a steeper bank which (under the same IAS) will result in an even higher rate of descent thereby getting me to the ideal glide slope earlier and leaving more time to fully stabilize before the threshold.

I use slipping turns all the time.

If you want to do a slipping turn you yaw the nose OUT of the turn, being careful to keep G loads low. It's NOT a dangerous maneuver if you keep speed up and nose down while doing it although you should use a bit more aggressive nose down than in a straight side slip to account for the slight extra G from the turn.  If you keep the wings largely unloaded and let the airplane fall semi-ballistically, you aren't going to stall.

To do it safely however, you do have to know how to fly the plane.


How to understand US military aircraft designation on the vertical stabilizer? There are many letters and numbers printed on the vertical stabilizer of US military aircraft. They identify the plane's design and purpose.

What are those letters and the meanings?

The number on the vertical tail is the aircraft serial number, not the type designation. Here the serial number is AF 41 823. The '4' is the last digit of the finacial year in which money was allocated to manufacture the aircraft and the remaining 4 digits represent the sequence number indicating the sequential order in which the particular aircraft was ordered within that particular financial year.

From USAF serials:

  Starting on July 1, 1921 (the beginning of FY 1922) a new serial number system was adopted based on procurement within each Fiscal Year. Each serial number now consisted of a base number corresponding to the last two digits of the FY in which money was allocated to manufacture the aircraft, and a sequence number indicating the sequential order in which the particular aircraft was ordered within that particular FY. For example, airplane 22-1 was the first aircraft ordered in FY 1922, 23-1 was the first example ordered in FY 1923, etc. This system is still in use today.

Apparently, USAF decided to have five digits in its tail number in 1958. This resulted in the cutting of first digit of the financial year.

  Camouflage began to reappear on USAF aircraft during the Vietnam War, and this led to a change in tail number presentation. The letters "AF" were added directly above the last two digits of the fiscal year, followed by the last three digits of the sequence number. The three-digit sequence number has a height of the AF and fiscal year letters combined and is sometimes called the "large" component of the tail number. For example, F-4E serial number 67-0288 had the tail number 67(small) 288 (large). This could of course lead to confusion, since aircraft 67-1288, 67-2288, etc would have exactly the same tail numbers as 67-0288 under this scheme. This would not ordinary cause a whole lot of difficulty unless of course some of these larger serial numbers also happened to be F-4Es (which they were not). Unfortunately, the system was not always consistent--for example F-4D serial number 66-0234 had a tail number that looks like this: 60(small) 234(large).

So, '4' represents the second digit of the finacial year, and 1823 gives the sequential number. The aircraft appears to be a F-100 Super Sabre. From f-100.org, the actual serial number appears to be 54-1862, a F-100C-20-NA model.