Why do helicopters have such limited range? Why do rotorcraft like helicopters have such limited range, rarely exceeding 1000 km on a full tank? For example, the range of the Apache is close to 425 km, and MI-26's is 800 km.

Helicopters are very inefficient in forward flight, for several reasons.

Consider Glauert's high speed assumption, i.e. the helicopter can be represented as an aircraft with a circular wing during high speed flight.  Now, if you know anything about basic fixed-wing performance, you'll realize immediately that this implies an aspect ratio just over 1, which is awfully small.  You may recall that for a fixed-wing aircraft, induced drag is inversely proportional aspect ratio--so a very low aspect ratio means very high induced drag!  Induced drag is normally not a big deal for fixed-wing aircraft at high speed because it's proportional to the square of the lift coefficient (which decreases with speed), but...
In reality, the situation for a helicopter is even worse!  Glauert's assumption assumes we have an ideal rotor, i.e. one that has a uniform induced velocity throughout.  In practice, the inflow distribution over the rotor is highly non-uniform, especially at high speeds where the advancing side of the rotor is in a very different aerodynamic environment than the retreating side.  Even on a very simple level, the "working area" swept on the retreating side is much smaller than that on the advancing side. Since lift needs to be balanced, momentum theory implies a higher induced velocity over the smaller area "worked" by the retreating side, and therefore a much higher induced drag at high speeds than an equivalent fixed wing aircraft.

Rotor wake computation from TsAGI RC-VTOL code (Kritsky, B.S).
As the helicopter goes faster, and as the rotor turns more slowly, more of the retreating side blade will stall, which leads to a dramatic increase in drag. This starts on the inboard section of the blades, and moves outwards as the advance ratio (ratio between flight speed and tip speed) increases.  In fact, the most inboard sections of the blade will even be in reversed flow--and airfoils don't work too well backwards.
On the advancing side, things are bad too, but for different reasons. The profile drag of the rotor increases rapidly with speed.  Moreover, as the advance ratio increases, the advancing tip Mach number also increases--and as the blades get into the high transonic regime, local shocks begin to form and lead to even larger increases in drag.  This can be delayed by slowing the rotor down, but that makes the problems on the retreating side even worse!  In general, it's hard to develop airfoils that work well in both regimes.
Outside of the rotor itself, the rotor hub is very draggy, between the main rotor shaft, pitch links, swashplate, hinges and blade grips, etc.  Helicopters usually have pretty "utilitarian" fuselages, as well, which are not so well streamlined.  Plus, you have the tail rotor, which has most of the same problems as the main rotor.
Back to the specific question of range, the Bregruet range equation says that the range of an aircraft is proportional to the lift-to-drag ratio and the speed of the aircraft.  We've already established that the L/D of a helicopter is pretty bad, especially at speed.  So, the cruise speed is going to be pretty low and the L/D is going to be pretty low, so to sum up, the range is going to be really low.

The tradeoff is that the helicopter is very good at hovering--even amongst VTOL platforms, the helicopter is the most efficient. Speed and range are the price you pay for that capability.


How much mathematics and what level should commercial pilots have? Continuing off the title, do different types of pilots require different mathematics level? Since as a pilot you have to calculate such as how much fuel will be used and needed, the weight of the cargo, etc. Since all of this will affect your flying since as how very heavy cargo will require more airspeed before taking off.

So there are potentially two ways to interpret your question. First is a pilot who holds an FAA commercial pilot certification, second is a societal occupation label generally referring to a pilot performing as a crewmember of a 14CFR Part 121 scheduled air carrier airway, or colloquially, an airline pilot.

In both cases the idea that any pilot need to be exceptionally capable at math is a fallacy. I suspect it's a holdover from the 40's and 50's when all flight planning calculations needed to be done by hand. Now all of that is automated and even allowed during the FAA written tests. Additionally, needing strong math skills is often claimed when an individual is actually thinking of a test pilot or aeronautical engineer, which both require very strong algebra and calculus skills.

That said, there are some areas in the higher level written exams that rewrite you know how to calculate weight and balance, but these all relay on standardized some equations that aren't exceptionally difficult for even a novice. These written exams include the Airline Transport Pilot (which will be required for the second interpretation), Dispatcher Certificate, and Flight Engineer.


What does the letter D on the underside of the wing stand for? Below is a picture of the Junkers F.13.

What does the letter D on the underside of the wing stand for?

(Image Source)

It stands for Deutschland. And the 366 is the remainder of the registration. The 'D' is the prefix to aircraft registered in Germany, think of it as an international license plate. The pre-1928 allocation was D-nnnn (max four digits).

Registration prefixes do not always have a clear meaning though.

For the placement, see here: Are the size and location of the registration number regulated?


Why does the rotor thrust decrease at smaller tip clearance for shrouded rotor? Consider this system, rotor with shroud:

From this research, we see that: at the same rpm, the rotor thrust decreases,the shroud thrust increases as tip clearance decreases. But why does the rotor thrust decrease at smaller tip clearance? You can see author said at page 11:

  "Note that the increased inflow in the plane of the rotor at smaller tip clearances causes a small reduction in the effective angle of attack seen by the rotor blade, which results in a small decrease in the rotor thrust."

I understand that the inflow increases that will causes a small reduction in the effective angle of attack seen by the rotor blade. But final question: why do we have increased inflow at smaller tip clearance?

This is the reason why a jet engine needs a shroud around its core: to reduce blade tip loss. When you decrease the wingtip clearance, you are curbing the wingtip vortices or the wingtip pressure bleed, and in doing so you are making each blade more and more effective at approximating its ideal i.e. infinite span high-low pressure spatial distribution under and above it, and this more ideal pressure difference accelerates the airflow better, which results in more inflow, which reduces the angle of attack of each blade a little, but increases the overall thrust produced. Think of the shroud as a big end plate for each and every blade. Think of this setup as the fan in a high bypass ratio turbofan: less fan tip clearance = more thrust.

EDIT: I'm not sure the author understood it as I do in his paper. He never clearly explained it in his writing. Plus, just why is there so much lift distributed at the wingtip? I've never seen anyone design a propeller with so much bending moment. He is making a propeller much heavier than it really is because the propeller could be less rigid and lighter and still providing the same thrust. If you really want an efficient prop, put the majority of lift near the midsection, and let the lift taper when approaching the tip.

EDIT: See how shroud works on a bona fide jet engine compressor:


Could a commercial plane like Airbus A320 glide with no working engines from 11000 meters? I have heard that pilots learn in simulators to fly also commercial planes without working engines, so that they glide. And still I have the impression, the chances that a plane could float from 11000 meters height are nearly 0. Could someone explain, if a commercial plain CAN BE THEORETICALLY (Physics) and PRACTICALLY landed from 11km with all failed engines? How important is the altitude from which all engines fail?

All standard fixed wing aircraft are able to glide. The key measure of performance in gliding is the glide ratio which is related to the lift-to-drag ratio of the aircraft. The glide ratio of a clean A320 is 17:1 which means it can travel 17 units of distance forwards for every 1 unit of distance downward at best glide speed. Using your figure of 11,000 meters away and multiplying by 17 results in a maximum range of 187km . In practice, the aircraft would need to be higher than this (or land closer) to accomodate turns and other factors, but if the A320 was at 1000 meters AGL or higher I would expect it to have no problem landing at an airfield or airport 11km away. Note that aircraft routinely glide every time you fly even though you may be unaware of it. When a commercial flight begins its descent often power will be brought back to idle, so the aircraft is gliding at that point.

There have been several instances of large commercial aircraft landing fully unpowered. One well known example is the case of the "Gimli" glider in which a Boeing 767 ran out of fuel and glided to landing at a nearby airbase.

EDIT: It has been brought to my attention that the OP is asking about a starting altitude, not how far away from the airfield. As I imply in my answer what matters is the ratio of altitude and distance, not altitude alone.


Can anyone identify the plane in the image shown and/or year of service? All I have is this photo, found in a collection of photo's which I'm trying to identify family members and an approximate date the aircraft is in service would help.  I've tried googling the aircraft Number but it only shows an Afro monoplane. The number is N 9732.
Any suggestions would be appreciated

I think it may be a Bréguet 14. Compare it to this photograph:

You can see the same two sets of vertical struts on the wings, which are quite distinctive, and the wing looks like it has the same large flaps, plus the large forward tail section. The fuselage has the same two step holes (at least, I assume that's what they are) seen on this photograph, and the rear seat is also just visible.
The related Bréguet 16 was slightly larger, with three pairs of struts, so it's not one of those; there was also a related Bréguet 17 which seems to have been visually quite similar, but produced in much smaller numbers. I suspect it may be after the war, as it does not seem to have a gun in the rear seat, and the number on the tail doesn't seem to match the wartime style of numbering. They were still knocking around into the late 1920s/early 1930s.
Bréguet 14s were fairly widespread, but I think these look like French markings. However, I don't know enough to be able to speculate on what "N 9732" might indicate in that context.


How is a transonic aircraft longitudinal stability different than a subsonic and supersonic aircraft? /I would like to know-how is the longitudinal stability is achieved between different aircrafts

At this level, there is nothing special about transonic stability.
Generally, airplanes become significantly more stable at supersonic speeds (due to aerodynamic center moving backward). At the same time, elevator efficiency drops. Transonic is simply the transition between the less stable subsonic regime and more stable supersonic regime.
Now, for an engineer as well as a pilot, transition can be a challenge, especially if it's quick. For example, most supersonic aircraft have variable stick-to-elevator ratio, and transition happens at transonic speeds. Apart from making sure that the aircraft is controllable throughout the transonic range, you need to consider what happens if the system fails at any stage.
As another example, modern fighters are often made longitudinally unstable. But this is only true at subsonic speed. They are all stable at supersonic regimes. Now you have transition between even more different states: unstable to stable (and back). Flight control systems must cope with that.
Thankfully, the transition is not too abrupt, especially for swept wings. (This, controllability, is in fact one of the main reasons to use swept wings. It's not just about drag).


Why is engine #1 still used when taxiing with one engine? According to the answer in this post Taxiing with one engine: Is engine #1 always used or do they switch? Engine #1 is used because it pressurizes the green HYD system which powers the Nose Wheel Steering. I found that, in latest model of A320 and A321, NWS is driven by yellow HYD system that is pressurised by engine #2. However, pilots still use only engine #1 if they want to taxi with one engine running.
Is there other reason for using engine #1?

  Source: Airbus AMM

According to the "Supplementary Procedures / Green Operating Procedures - One Engine Taxi" in section PRO-SUP-93-20 of the A320 FCOM:

  Use Engine 1 for taxiing because it pressurizes the green hydraulic system (normal braking).

and

  Y ELEC PUMP.............................ON
  This pressurizes the yellow hydraulic system (nosewheel steering) without using the PTU.


What could cause a low-pressure compressor first stage blade of a turbofan engine to bend forward? What could cause a low-pressure compressor first stage blade of a low-bypass turbofan engine to bend forward?

I also noticed rotor path rubbing in the 9 to 12 o'clock portion (while usually this can happen only in the 6 o'clock area).

Forward bending of the first stage of the low pressure compressor is usually associated with (soft) Foreign Object Damage (FOD).

Ice and/or large quantities of snow in the engine intake will typically cause forward bending of the leading edge of the tip of the blades.

 Damage to GE CF680C2 turbine engine compressor fan blades after snow/ice ingestion
Source: Flight Safety Australia

 Damage to Turbomeca gas turbine Arriel 2B turbine engine compressor blades after snow/ice ingestion
Source: Transport Safety Board of Canada, aviation accident investigation report A12P0008


What is the equation for the energy balance between turbine, compressor and propeller? Let's consider the next turboprop arrangement:

What I am looking for

I am looking for an equation that involves $\dot{W}_T$, $\dot{W}_C$ and $\dot{W}_P$ (i.e. the power done by each component). This needs to be done through an energy balance in the shaft.

What we know

We know that the shaft has an efficiency of $\eta_{\text{shaft}}$, and the gearbox has an efficiency of $\eta_{\text{box}}$.

My try (#1)

Since energy is derived from the turbine, we adopt the convention $\dot{W}_T>0$, therefore $\dot{W}_P, \dot{W}_C < 0$. In other words, energy is required to move the compressive devices.

Following the definition of mechanical efficiency: $$\boxed{\eta_{\text{shaft}}=\dfrac{-\dot{W_C}-\dot{W_P}}{\dot{W_T}}}$$

However, I don't know how to incorporate the efficiency $\eta_{\text{box}}$ into this equation. This led me to try and find another expression.

My try (#2)

Following an hydraulic analogy for the power, I thought that whatever power the turbine generates needs to be invested in:

Increasing the temperature of the bearings of the main shaft (because the shaft is not ideal and has an efficiency of $\eta_{\text{shaft}}$).
Moving the compressor.
Increasing the temperature of the gearbox (because the box is not ideal and has an efficiency of $\eta_{\text{box}}$).
Moving the propeller.

Following this thinking, I can intuitively find this next equation (which I don't know if is correct or not): $$\boxed{\eta_{\text{shaft}}\times \dot{W}_T = -\dot{W}_C-\dfrac{\dot{W}_P}{\eta_{\text{box}}}}$$

The thing is I don't know if I assigned the efficiency $\eta_{\text{box}}$ correctly or not. Is there an easier way (i.e. less intuitive/more mechanical way) to apply the energy equation? What if we had 2 or more shafts?

Since the compressor loses a fraction of the turbine's work through the shaft, but is unaffected by the gearbox, but the prop experiences losses from the shaft and the gearbox, this equation should be what you need:

$$\dot{W_t}=\frac{-\dot{W_c}}{\eta_{shaft}}+\frac{-\dot{W_p}}{\eta_{shaft}*\eta_{gearbox}}$$

Which is the same as your attempt two (with some algebra).

As you add more efficiencies to a component, you would just continue to multiple the all $\eta$'s together to get the total efficiency of that component, since efficiencies are multiplicative and the associative property of multiplication.


How do I find the historical arrival procedure GOLDN6 for SJC that is no longer valid? I don’t know exactly when this procedure disappeared.  It was used in 2013, but not sure how much longer.  It was used primarily by SEA to SJC flights.

I'd google it & look thru the results until you find one that has the arrival depicted.
Understand that the numeric part of the arrival (6 in GOLDN6, for example) changes over time. Maybe the FAA adds, or removes, or changes a speed restriction at a given waypoint on the arrival. The number will go up, and the new version will be effective on a given date. Then in some number of months, something else changes, and the number increments again. When it gets to 9, the next revision goes back to 1.  (Which is okay, since the last GOLDN1 was now years in the past, and what's important is differentiating the current procedure from one that was recently superseded.)
Typically, these revisions are pretty minor, and when airspace gets revised on a large scale, the old procedure names are all retired, and all new procedures are published with all new names.
All of that to say, if you search for "GOLDN arrival SJC" (and don't let the search engine helpfully substitute 'golden' in the query), you may find a chart of the GOLDN4 or GOLDN5, which would most likely be quite similar to the one you're interested in.
I imagine that the FAA TERPS office keeps archival copies of everything that they've ever published, as (probably) would OAK Center and the NORCAL TRACON, and (almost certainly) Jeppesen, but those avenues start becoming a lengthy research project, trying to get in touch with the right person in the right office.
So I'd peruse search results first.


Is there a maximum or minimum temperature for take-off and landing? Is there a maximum or minimum temperature that a plane can take off or land at?

There is a maximum temp but that varies by airport altitude, runway length, aircraft and payload. You can find an answer to that question here.

There is not really a minimum temperature but it needs to be warm enough out to run the engines. Again this varies by aircraft and a preheat can usually solve this problem but there are places on earth where it be comes practically to cold to operate some aircraft. On a similar note if icing conditions prevail you are not really going anywhere but those can occur at lots of altitudes and temperatures. If the given airplane is stored outside and the airport lacks proper de-ice equipment you may be grounded.


What physical tests are involved with verifying a wing spar is suitably constructed for a homebuilt aircraft, such as the piper cub kit from wicks? During construction how is a spar tested to ensure it can adequately cope with bending and twisting forces of the completed structure, or is this performed after complete?

For a homebuilt a static load test is required. Whereas a full certification would require a loading to 1.5 the maximum load, this factor is reduced for experimental aircraft to 1.0. But performed it must be nonetheless.

For the test the aircraft is propped up upside down and sandbags (or water bottles) are placed on the wing until the calculated load is reached.

Structural test of the Electra One (picture source)


Are ducted fans more efficient? As far as static thrust, does a shrouded/ducted propeller outperform an un-shrouded propeller? It seems that the guide blades on the bottom of the duct would allow little more thrust to be extracted from the vortex the prop generates by redirecting the air flow. Also the duct seems like it could "focus" the propelled air (like a rocket thruster) resulting in better thrust.

(Source)

Of course I can see how an improperly implemented duct could really kill efficiency (creating more interference and turbulence), but what about a well designed one? And if they are better, why wouldn't we seem most propeller aircraft use them (what is the advantage about not having the duct)?

there is a lot going on here.  Short answer is that a ducted fan (what you have pictured) can produce a lot more thrust (experiments from one paper say twice as much) than an open rotor of the same size.  The big thing that these ducted fans have going for them is the fact that tip losses become negligible because there simply isn't room for the tip vortex to develop because there is a duct in the way!  Simple, easy solution that works well.

However, nothing comes for free.  One, you have to have the duct there, which is weight & money (you have to build the duct and the support structure, which adds some drag too).  Think of scale too--as propellers get larger, the duct has to grow with them.  Imagine the difficulties in putting a 20' duct on a B-36 propeller!

Second, the manufacturing tolerances on the duct are critical--the tighter it is, the more efficient you are (to a limit, naturally)...but the tighter it is, the more susceptible you are to having your blades strike the duct due to flexing of the duct or the blades.  And, speaking of flexing blades and the necessary support structure you'd need, this could make pitch control (on a propeller, variable pitch, and on a rotor, cyclic and collective) difficult to implement, depending on which of those schemes you're looking to do.  Then again, for a small implementation using RPM control...maybe you don't need those anyhow.

Similarly, while a crosswind on an open rotor leads to a sudden decrease in power, a crosswind on a ducted fan leads to a sudden pitching moment due to the lip of the duct and the asymmetric inflow to the fan (which, since you're now producing more thrust to begin with, asymmetric inflow effects become even more pronounced).  Now, if you stick this on the front of a typical Cessna 172, say, and throw a crosswind at it (which, if you think of takeoffs and landings, which since they must be in a certain direction, having a crosswind is actually quite likely) imagine the yawing moments that would be induced by the propeller (proportional to the static thrust) -- even before the aircraft got off the ground and before you have a lot of control authority to counteract it!  A similar scenario in the air could be as dramatic.  And, yeah, you could throw some guide vanes at it to help, but nothing comes for free.  Guide vanes, which is a workable solution, now mean that you need to have actuator(s) for those vanes, power & maybe hydraulics for the actuator(s), mounts for the actuators, hinges for the vanes, linkages from the actuator(s) to the vanes, redundancy for the actuation or some means of facilitating control in an emergency...it's a lot of work.  Or, by contrast, you could just bolt a fixed pitch prop on a shaft at the front of said Cessna 172 and call it a day.

In the long run, and this is some speculation, I think it just leads to a more complex system, particularly in full-size implementations, which is a maintenance, cost, and manufacturing headache that isn't worth having if you can get plenty of performance from a regular open propeller.  If you venture into the world of diffuser augmented wind turbines, there have been similar debates going on for decades...and a ducted wind turbine has yet to be successful on the large scale.  Similarly, while ducted fan aircraft have flown...

(Ryan XV-5A Vertifan, circa 1950.  The ducted fans are underneath the circular domes on the wings and another under the shuttered area on the nose for pitch control. Source: http://www.aero-web.org/specs/ryan/xv-5a.htm)

...there aren't any non-MAV examples around today that I know of.

Source:
https://theses.lib.vt.edu/theses/available/etd-05262005-170916/unrestricted/WGraf_Thesis_2005.pdf


Is it possible to predict how busy an airport will be in a given time? (are there existing services that to this?) I want to know if it's possible to predict how busy an airport will be at a given day or part of day.

I know there are services that provide the scheduled flights in an airport

Is there also an API that allows programmatically accessing this data (preferably for free)
How far in advance are the flights scheduled and the data published?

The distribution between 'regular' passengers and 'connecting' passengers is also important (a passenger during a connection has a much lower effect) - it the data of how many passengers in a flight taking a connection available? (even long term statistics)

This is a bit of a different approach than you were thinking, but Google estimates how relatively busy a place is based on location data:

This can be found in the right-side bar if you search for an airport code or many other locations. It's based on their location data, not flight schedules.


On the 737 MAX, can the pilots switch to the backup MCAS, or switch active MCAS input to another AoA probe during flight? According to this article, my assumptions about the Boeing 737 MAX flight control system are (please correct me if I am wrong):

The aircraft has two flight control computers (FCC)
The aircraft has two angle of attack (AoA) probes
The Maneuvering Characteristics Augmentation System (MCAS) is implemented as a function of each FCC
Data from the port AoA probe is supplied only to FCC 1
Data from the starboard AoA probe is supplied only to FCC 2
Only one FCC (FCC 1 or FCC 2) is active during each flight, with the other serving as a backup system

Assuming a situation where only the AoA probe used by the active FCC produced incorrect AoA information and thereby causes the MCAS to intervene while the other AoA probe is functioning correctly, would it be possible to either

switch to the other FCC (which uses input data from the other AoA probe)

or

switch the active FCC to use input data from the other AoA probe

and thereby prevent the MCAS from continuing to use incorrect AoA data?

As far as I understand from reading the B737 Operations Manual and the Lion Air Accident Investigation report,

Each Flight Control Computer (FCC) receives AOA input only from the onside ADIRU and vane.

  The AOA and Mach inputs are provided to each FCC by the associated Air Data Inertial Reference Unit (ADIRU). Each ADIRU receives AOA information from one of the two resolvers contained within the associated AOA sensor (i.e. the Left ADIRU uses left AOA vane and the Right ADIRU uses the right AOA vane).

  Source: FINAL KNKT.18.10.35.04 Aircraft Accident Investigation Report

The Maneuvering Characteristics Augmentation System (MCAS) and the Speed Trim System are controlled by the master FCC, which alternates between A and B per flight.

  Similar to the Speed Trim Function, the MCAS function is also a flight control law contained within each of the two FCCs. MCAS is only active in the master FCC for that flight. At aircraft power-up, the master FCC defaults to the left side FCC; and will then alternate between the left and right FCC by flight.  The master FCC is not affected by the position of the Flight Director switches.

  Source: FINAL KNKT.18.10.35.04 Aircraft Accident Investigation Report

This master FCC is different from the master FCC used to compute for the Flight Director (F/D) and the autopilot (A/P). For the purpose of AFCS, the master FCC can be cycled via the F/D switches on the Mode Control Panel (MCP), and the master FCC is illuminated.

  The master FCC is indicated by illumination of the respective master (MA) F/D
  indicator light. The master FCC is determined as follows:

  with neither A/P engaged in CMD, the FCC for the first F/D turned on is
  the master
  with one or both A/Ps engaged in CMD, the FCC for the first A/P in CMD
  is the master FCC, regardless of which F/D is turned on first.

  Source: Boeing 737-600/-700/-800/-900 Operations Manual

There does not appear to be a way for the crew to know which FCC is actively controlling the MCAS, nor a switch out the controlling computer, apart from pulling the circuit breakers.


How are the costs managed in a codeshare? How do the airlines manage the costs invovled in a codeshare?

As all airlines are selling tickets, (might be at different prices) but only one of them is operating the flight.  So, how do the airlines decide who will pay how much for the crew, fuel and catering and who will earn what?

And how do you justify:

  When an airline sacrifices its capacity to other airlines as a code share partner, its operational cost will generally be reduced to nil. (Source:Wikipedia)

As the wikipedia article clearly states, there are several types of Codeshare Agreements :

  Block space codeshare: A commercial (marketing) airline purchases a
  fixed number of seats from the administrating (operating/prime)
  carrier. A fixed price is typically paid, and the seats are kept away
  from the Administrating carrier's own inventory. The marketing airline
  decides on their own which booking classes the seats are sold in (the
  block of seats are optimised just like another aircraft cabin).

  Free flow codeshare: The airlines' inventory and reservation systems
  communicate in real-time by messaging, commonly IATA AIRIMP/PADIS
  messaging (TTY and EDIFACT). A booking class mapping is defined
  between the airlines. No seats are locked to any of the airlines, and
  any airline can sell any number of seats.

  Capped free flow: Basically the same as above, but a capping (max
  number of seats) are defined for each of the marketing airlines
  participating in the codeshare with the Administrating
  (operating/prime) carrier.

In these cases, profitability of the Airline Marketing the other airline's tickets is possible in any of the following ways:

There might be an agreement with the Carrier Airlines where the Marketing Airline gets to sell the tickets at the same rate as being sold by the Carrier Airline,but the Carrier Airline sells the tickets to the Marketing Airline at lower prices. This helps the Marketing Airline to generate revenue and improve its indicated (apparent) frequency on the given route. The Carrier Airline is benefited in a way where its tickets are sold on more than one portals, so better visibility (Marketing) and hence the name.
Now a days alliances like OneWorld are being formed, where multiple carriers come together and form codeshare bases to mutually benefit each other.
The Marketing Airline might even sell the tickets at a cheaper price than the original Carrier Airline, just to establish its base in the route before starting its operations, so that when it starts its operations, people already know about it. hence, without deploying planes for the route, it can already have an established consumer base.


For military helicopters, what is the typical fatigue life of the main rotor dynamic components? For military helicopters such as the Sikorsky UH-60 Black Hawk:

What is the typical fatigue life of these helicopter main rotor dynamic components in cycles and hours?

a) Main rotor pitch links (aka main rotor push rod)

b) Main rotor pitch change horn

c) Main rotor blades

Helicopter or Rotary Wing Terminology

The fatigue life of helicopter dynamic components is determined by the manufacturer based on the number of hours flown and as such, varies from helicopter to helicopter.

In general, life of the dynamic components are less than that of the helicopter structure. The life of the dynamic components depend on the fatigue loads (the magnitude and load spectrum) and the materials used.

So, the same helicopter involved in more demanding operations (civil vs. military) will have less life. Actually, during development, the fatigue life is determined in number of cycles, which is then converted to flying hours based on the expected flying pattern. Also, the materials used make a difference, with composite materials having better fatigue resistance compared to metallic blades.

The life of the UH1 MRB (Main rotor Blade), for example is around 2500 hours. For UH60 MRBs, similar values have been quoted for metallic blades. However, Studies by MBB (Now part of Eurocopter) indicate that the composite blades under normal loading have a fatigue life of around 4000 hrs (AGARD conference Proceedings No. 297, Helicopter Fatigue Life Assessment).

The life of other dynamic components, e.g. pitch horn, pitch link etc. are usually around 1000 hours. However, with little data available in public domain for helicopters under service, it is hard to say with any certainty.

It should be kept in mind, however that these values are only indicative as all dynamic components are periodically checked using NDT methods and decision on their continued service is solely based on the results of these tests. For example, any damage to the bearing in the pitch links will result in their replacement. Also, the development of Health Usage Monitoring Systems (HUMS) means that most of the H/c manufacturers are moving away from a life based approach to a health based approach, resulting in variation in life of individual components.


Can I fly a "Contact Approach" to this airport? In order to request and receive a clearance to conduct a "Contact Approach" the airport, among other requirements, must have a published instrument approach (IAP) and be reporting at least 1 mile visibility.

If the visibility being reported for this airport (Lake Tahoe -TVL)  is 2 miles, and thus below minimums for any IAP, would it be legal to conduct a "Contact Approach?"

(The two IAPs shown below are the only published approaches and the plates have been trimmed for brevity.)

Here are the requirements for a contact approach from the AIM 5-4-25:

  Pilots operating in accordance with an IFR flight plan, provided they
  are clear of clouds and have at least 1 mile flight visibility and can
  reasonably expect to continue to the destination airport in those
  conditions, may request ATC authorization for a contact approach.

If all those things are true then you can request a contact approach (ATC can't offer it). But ATC has requirements to meet too:

  Controllers may authorize a contact approach provided:

  The contact approach is specifically requested by the pilot. ATC cannot initiate this approach. EXAMPLE− Request contact approach.
  The reported ground visibility at the destination airport is at least 1 statute mile.
  The contact approach will be made to an airport having a standard or special instrument approach procedure.
  Approved separation is applied between aircraft so cleared and between these aircraft and other IFR or special VFR aircraft.

If those things are also true then ATC can authorize it but there's no guarantee that they actually will.

In the example you gave, it looks to me like all the requirements are indeed met (although you didn't say whether the two-mile visibility is flight, ground, or both), so a contact approach would be legal. There's no requirement to comply with the minimums for a published approach during a contact approach.


What is a navigational fix? Where can I get navigational fixes for a local airport? Amateur in aviation, so please explain the purpose of navigational fix and its characteristics. How is a navigational fix being placed around the runway, or how it is determined this would be the right spot? How does it help a aircraft to make it land?

And where would I get the details of navigational fixes for a airport near me? Is there a API, does ICAO provide any info?

Any links/charts could be of great help.

A navigational fix is a waypoint that can be used to navigate to, from or between airports or other navigational fixes. Navigational fixes can be GPS-based coordinates, radio-based navigational aids like VORs or NDBs or airport themselves, which have a defined airport reference point with set coordinates.

Navigational fixes or aids are usually not placed around runways, but those that are used for approaches or departures (mostly VOR or NDBs) are placed at or in the vicinity of the airport. See below for the placement of the Barmen (BAM) VOR, which is one of the approaches fixes used for the ILS approach to runway 23L and 23R and the, nowadays no longer used, NDBs DX and LI as the outer markers for the instrument approach.

(Image Source: www.skyvector.com)

Navigational fixes required for approaches or departures to a specific airport will be available in the countries' AIP, in the publications for the specific approach or departure routing, e.g. navigational fixes along a STAR or Transition from the Initial Approach Fix (which is a navigational fix as well) to the Final Approach Fix.

(Image Source: VATUSA)

The above displays the navigational fixes for the transitions/arrivals into Memphis International Airport.

For a list of available radio navigational aids around an airport, you can try sources like SkyVector.


How do most fighters slow down after landing? I understand that many fighters use drogue parachutes and wheel brakes. But aren't there other methods of slowing down after touchdown?

The primary (and most effective) method to slow the jet down is aerobraking.

In the T-38 at ~130 knots full aft stick is applied at a rate that prevents the jet from becoming airborne again.  The stick will be back towards the seat pan.  Fly the nosewheel down to the runway at ~100 knots and apply wheel brakes.

In the F-16 the max aerobraking occurs at 13 AOA with speed brakes extended.  You do not want to exceed 15 degrees of pitch angle to prevent scraping the burner can and speed brakes.  The speed brakes will not fully extend while the nosewheel is not on the runway (however, it can be overridden but increases the possibility that the speed brakes will scrape).

In either case you do not want to let the nosewheel fall.  You also do NOT apply wheel braking until the nosewheel is down.


How to calculate the radius of a turn as a function of speed, bank, wing-loading, and Cl? Although the question of how to calculate the radius of a turn of an aircraft has been answered before using only the speed and the bank angle, the reality is that 2 aircraft with the same speed and bank angle will have a different radius of turn if their wing loading is different.
Furthermore, two aircraft with the same speed, bank angle, and wing loading will not necessarily have the same radius of turn. The lift coefficient of the wing must be taken into account.
Since the answer posted before is not complete, can somebody provide an equation that takes into consideration the above factors (and any others that should be contemplated)?

The formula for turn radius is Velocity squared divided by radial G. And since Radial G, (assuming a level turn) is absolutely dependent on bank angle, the turn radius IS absolutely dependent on Velocity and bank angle. No other factors are necessary.
You are incorrect that two aircraft with different wing loading will have different turn radii at the same airspeed and bank angle. Anyone who has flown formation, even if they are not familiar with the physics/mathematics involved, knows this from experience.


How common are aprons made of bricks? I found this topic on an external site, it's about a Boeing 737-4 damaged during engine run up at Sialkot international Airport (Pakistan): NL B734 Damaged During Engine Run Up (photos)
In the comments/discussion, people say that there is similar apron paving made of blocks at other major airports.

Are there any photos or verification of lose-block apron?

One comment says that London Heathrow has some, does somebody have any verification or Link?

Block paving is very common at airports. All over Heathrow and Gatwick. It works fine when its built correctly but if it's not maintained well then that happens.

Hong Kong International Airport represents the largest single airfield installation of interlocking concrete pavements. Since most of the airport is on reclaimed land, anticipated settlement required that flexible asphalt pavement be used instead of rigid concrete for runways. Concrete pavers also provide a more fuel-resistant surface than asphalt.

Source

See also

Concrete Block Paving
for Airfields
Airfield pavement design with concrete pavers
Evolution of Interlocking Concrete Pavements for Airfields
THE USE OF INTERLOCKING CONCRETE BLOCKS ON AN AIRCRAFT PAVEMENT IN AUSTRALIA


What is the heat signature of a piston engine, relative to a jet engine? I'm reading about the AIM-9 Sidewinder Missile again. I noticed this interesting photo:

Notice, that's a piston-engined aircraft, and a small one at that. So I'm asking myself, how did the missile lock onto it? The AIM-9 is a very early heat-seeking missile (~1956). I thought early heat-seekers could only lock onto a jet engine, which I believe has a much larger heat signature than a piston engine.

Now I know today that IR missiles can lock onto almost any heat signature, even the heat of the adiabatically compressed air at the wings' leading edge. But in 1956, I'm surprised that an IR missile could lock onto a piston engine's heat.

So I want to start with this question: What is the heat signature of a piston engine, in terms relative to a jet engine? 2x less? 3x less? Or somehow equivalent?

Here is a color IR image of what I believe to be another F6F, on the tarmac shortly after landing:

As you can see, the engine cowling is very noticeable, as are the tires (from touchdown and braking).

Here's a similar image of an F/A-18 performing a runup test prior to takeoff. This jet is longer and larger than the F6F (though if you've ever stood under a Hellcat you'll notice they're not exactly small planes), and as you can plainly see, the entire back half of the aircraft glows white-hot:

So clearly jets are more visible targets for an IR missile, though a prop plane wouldn't be that hard for an IR seeker to find.

The biggest issue relating to getting a good IR lock and track is contrast. Against a blue sky, almost any airplane is readily visible to the missile's seeker. The biggest problem for combat aircraft in early engagements was firing at a target below the horizon (so-called "look-down, shoot-down"). This was a problem for both radar and IR technologies. For IR, solar heating of the ground produced high enough temperatures that the aircraft could not be distinguished unless it had turned its tail to the shooting aircraft and was showing its 600-degree exhaust plume. Nothing on the ground underneath it would be that hot. Prop planes, while operating at lower temperatures, would still be warmer than the ground, and unlike a jet the aspect angles at which this heat is most noticeable is around the front half of the aircraft.


How does ILS (Instrument landing system) work? How does ILS (Instrument landing system) work?

I know it provides guidance to the runway by  two signals, one modulated at 90 Hz, the other at 150 Hz, but how the airplane lock on those signals?

Which system in the plane is responsible for the ILS? Is the autopilot responsible for it?
If autopilot is used for an ILS approach, at what point does the pilot take manual control?

The ILS works using two components, a localizer and a glideslope.  The frequencies for the localizer are between 108.1-111.95 MHz and the glide slope between 329.15-335.0 MHz.  These frequencies are the carrier waves that the modulation you mention takes place upon.  A pilot is only concerned with the localizer frequency as the navigation equipment knows the paired glideslope frequency for any given localizer frequency.

The equipment for transmitting the signals is pretty well described in your question.  The localizer antenna broadcasts two lobes down the length of the runway for a few miles (typically 18 nm, but some airports like LAX have a much longer serviceable distance).  The glideslope antenna sits around the 1000 ft touchdown zone markers on the runway, offset a little bit from the runway.  It broadcasts a its own two lobes centered around a 3 degree slope (this can vary by installation).  The glideslope is generally usable about 10 nm from the runway, but is generally not used that far out.

The equipment in the plane responsible for using this signal comes in a few parts, an antenna, a radio and a navigation instrument.

The localizer signal is received the antenna used for the normal navigation signals (VOR) and there will be an additional antenna for the glideslope signal.  These signals will first go to a nav radio, which the pilot uses to select the localizer frequency (or a VOR frequency).  If a localizer frequency is selected, the radio will also listen on a specific glideslope frequency.

The data from the radio is then sent to whatever instrument you are displaying the data on.

The most primitive instrument is the VOR head with glideslope-type of needled navigation instrument.

A step up from that is an HSI, which is a bit more intuitive to fly and has better facilities for handling localizer back courses.

On the top end you have electronic primary flight displays that display data on a CRT or LCD screen.

The basis of all of these are following two needles that are shown to the pilot.  One moves side to side and tracks the localizer, and the other moves up and down and tracks the glideslope.  If both of these are centered you are in the middle of both beams and on course.  The position of the needle is determined by which lobe of the transmitter is being received stronger than the other.  When both lobes are received equally the needle will be centered.

To your last question, the pilot has control over the airplane for the entire approach.  The ILS does not take over the airplane.  The autopilot may be slaved to follow either just the localizer, or both the localizer and glideslope, or the pilot may hand fly the approach.  In both cases however, the pilot is in control, not the ILS.

The ILS is usable for at least 10 miles from the antennae.  At many airports you will track the localizer portion of the signal much further out than this.  You will stop using the ILS normally at 200 ft above the ground, although there are special ILS approaches with lower minimum altitudes that require special equipment and training. The majority of ILS approaches however, require the pilot to observe certain visual cues before descending below 200 ft AGL.


Does an airplane has to take off from beginning of the runway or it can take off from displaced threshold? I mean, if the airports declared that there is a displaced threshold of runway ; and airplanes use this length for landing but how about for takeoff?

Can the displaced threshold be used for takeoff?
The part of the runway in front of the displaced threshold must not be used for landing (it can be used from the other direction during roll-out), but it may be used for takeoff:

Displaced Threshold. A displaced threshold is a threshold located at a point on the runway other than the designated beginning of the runway. Displacement of a threshold reduces the length of runway available for landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction.

(FAA AIM Chapter 2 - Section 3 - Airport Marking Aids and Signs)
This also follows the ICAO definitions in Annex 14, Volume 1, Attachment A, Volume 1, 3. Calculation of declared distances:

The declared distances to be calculated for each runway direction comprise: the take-off run available (TORA), take-off distance available (TODA), accelerate-stop distance available (ASDA), and landing distance available (LDA).

Where a runway has a displaced threshold, then the LDA will be reduced by the distance the threshold is displaced, as shown in Figure A-1 (D). A displaced threshold affects only the LDA for approaches made to that threshold; all declared distances for operations in the reciprocal direction are unaffected.

(Landing Distances on SKYbrary)
Note that the TODA (TakeOff Distance Available) is unchanged in D, but the LDA (Landing Distance Available) is reduced.
Does it have to be used for takeoff?
No, a takeoff can be performed starting from anywhere along the runway. This is typically called an intersection takeoff. Some airports even have taxiway signs displaying the remaining TORA at some taxiways:

(ICAO Standards - Airfield Information Signs)
Such an intersection takeoff requires ATC clearance and of course that the aircraft takeoff performance calculations are done based on this intersection. See also Are intersection takeoffs less common in the USA than in other countries?


Is it a good thing that ailerons remain deflected and the stick is hard to move? The aileron stick of my homebuilt ultralight is stiff (hard to move) and the aileron itself can remain in its deflection angle hands free, is that a good thing?

The controls of any aircraft should move easily under the pilot's control.  Large aircraft have hydraulic servos to assist the pilot, or even complete fly-by-wire systems, while smaller aircraft often have aerodynamic trim tabs which act as a simple assistance mechanism.  On the ground, with no aerodynamic loads, the controls should move easily without such assistance, especially on an ultralight.

I would suspect that your control cables or pulleys are binding on something, or that the pivots of your cockpit controls or control surfaces are over-tightened.  Either of these could result in premature wear and failure in flight, as well as the more obvious difficulty in maintaining control before failure.  You should definitely investigate the cause thoroughly before attempting flight.


When filing a VFR Flight Plan, where/how do you include intent to use a Class B transition? When intending to use a VFR transition route through Class B airspace, do you put the intended route on the flight plan, the alternate route (if you don't get clearance for some reason), or both?
Which fields does the information go in? e.g. Does the intended route go in route of flight and the alternate in "Other Information" or vice versa?
Example:
I am planning to fly from KHAF to KAPC. Ideally, I'd like to fly using the Bay Shore Transition, as marked on the SFO TAC:

KHAF VPSCS VPOYS VPSBT KAPC

If I'm not cleared into the Class B, I'd instead fly

KHAF SAU KAPC (staying outside the Class B)

How would I file this plan?
Where does one request a VFR transition route through class B? deals with the ATC, not the filing.

Here is the form I will be using:

Since VFR flight plans are only used for SAR, and your route would only matter if you aren’t talking to ATC, I would file the route you intend to take if ATC denies you the B transition—or refuses to talk to you entirely.
If they do talk to you and grant the transition, then there will be a clear record of your actual path, and nobody will bother to look at (that part of) the route in your VFR flight plan. Or any other portion of your route where you have Flight Following, for that matter.
Note that, for calculating ETE and required fuel, Murphy’s Law says you should use whichever route is longest.
If you’ll be getting a WX briefing, mention the possible diversion to ensure your briefer checks that area too, but realistically, you won’t get in if there’s anything there serious enough to matter.


Do modern jet engines monitor and record exposure to particles of dust or sand? The BBC News article The Jet Engines with Digital Twins describes engineers monitoring measured versus modeled behavior of jet engines, and deviations between them signaling possible need of maintenance.

The following mention of sand:

  One of the most useful parts of the digital twin is that it measures a huge number of factors that the engine faces throughout its lifetime -- some flights have more people on them then others (that will put more strain on the engine), some cities (like Abu Dhabi) have a lot of sand in their air, and some pilots push their engines harder than others. “With the twin...I can learn that the pilot is a cowboy and pushes the engine. The fuel burn we see will be different with different pilot. The digital twin remembers every one of those events. (emphasis added)

made me wonder if modern jet engines monitor and record exposure to particles of dust or sand. If so, roughly how do the airborne particle monitors work - do they monitor the size distribution, or just count number over a certain threshold of some kind?

As of now, there are no commercially available engine particle ingestion sensors, though a few are under development. One of the companies involved in development lays out the reasons for the absence of any such sensors:

  As of today, no commercial off-the-shelf particulate sensor is in use because of the special design and difficult requirements for operation and performance in this harsh environment, according to Dr. Hai Lin of Hal Technology in Fontana, California.

There are multiple sensors under development like the Dual Optical Embedded Dust Sensor which is used to determine the particle ingestion by the AGT1500 engine in M1 Abrams, where dust and sand is a bigger problem, if anything.

All of these sensors work on a similar principle- they measure the scattering of light by the particles using a optical sensor.

  The sensor detects light scattering from moving particles as optical pulsed signals whose amplitudes are proportional to size and whose number is proportional to concentration. This sensor technology can determine particle size, distribution, concentration and further be extended for composition.

In future most of these systems are expected to available commercially, as

  While continuing to advance this technology for particulate composition determination, Hal Technology is pursuing a licensing agreement or partnership with sensor or engine manufacturers to have the sensor integrated into engine heath management systems of the future.


Why can't airline pilots listen to music while flying? In an interview I read, a 747 captain (Mark Vanhoenacker, an American British Airways pilot) says he doesn't understand why he cannot listen to music inflight, when for example surgeons – who literally hold peoples' lives in their hands – can:

  Can you ever play music in the cockpit?
  Sadly no. Sometimes when your flight is delayed, on the ground waiting
  for a couple hours, without passengers on board, you might put some
  music on in the cockpit. On the radio, you might hear a little music
  break through on an air traffic control frequency, those frequencies
  aren't much higher than the ones used by commercial radio stations.
  But as for listening to music while flying, no—which I don't
  understand! I think surgeons can listen to Beethoven if they want,
  right?

I looked that up and sure enough, some surgeons really listen to music and it even improves their performance:

  "From classical to rock, music can be heard in operating rooms across
  the world. When plastic surgeons listen to music they prefer, their
  surgical technique and efficiency when closing incisions is improved,
  a new study shows."

So why is it not allowed for airline pilots ?

I don't know where he gets that.  Regulation wise there's nothing stopping an airline pilot from listening to music as long as he/she can hear ambient sounds or communications and modern headsets make it easy to link an ipod to headphones that are also receiving the comms.

Pilots are allowed to take naps in flight as long as they are awake within 45 min of arrival.  A pilot not flying (PNF), where the autopilot is on and the other pilot is monitoring everything, can be doing paperwork or reading a paper or watching a movie on a tablet or going for a dump or wandering around the cabin if he/she wants.  Once on an arrival however, forget it and certainly not once below 10000 ft.

If there is a prohibition in that Capt's case, it is probably a policy with that airline.


What are the considerations for landing on ice runways? In Greenland there are a number of ice runways and I have heard that it is no difficulty landing on them. One would think they would be slippery and the aircraft might slide off the runway or ground loop. However apparently that does not happen.

Are there any special considerations for landing on an ice runway? Is there an increase in minimum landing distance?

In Greenland there are a number of ice runways and I have heard that it is no difficulty landing on them. One would think they would be slippery and the aircraft might slide off the runway or ground loop. However apparently that does not happen.

Yes it does.  Go to Youtube and search for "Alton Bay Ice Runway" for examples.

  Are there any special considerations for landing on an ice runway?

First, understand that you are making a short field landing, NOT a soft field landing.  A soft field landing (well, mine anyway!) will eat up much more runway length.  Ice is hard, and you can hammer it down if necessary.

Second, do not use your brakes until under about 5 knots. Use aerodynamic braking instead.  Yoke full back on the ground.

  Is there an increase in minimum landing distance?

Yes!  Aerodynamic braking is pretty ineffective below 20-30 knots.


Is it possible to tow a smaller aircraft (like a LSA with a non-functioning engine) with a more powerful towplane? The idea is to move an otherwise flyable aircraft with a bad engine from an airstrip with no facilities, to an FBO with a AP mechanic available for an engine swap. Let's say perhaps 100-200 miles, VFR conditions, takeoff, climb to cruise altitude, descent, and landing.

Yes.
I know of a pilot in the USA who has done exactly this.  Both aircraft were Cessna 182s.  The aircraft to be towed was outfitted with a releasable tow hook mounted on the prop shaft (I believe the prop was removed).  It took a lot of effort to satisfy the FAA that this could be done safely.  Part of this effort included videotaping towing a Cessna 182 (the one that ended up being the towplane) into the air via the same prop shaft-mounted towhook with a motorcycle on a long 7000' runway.  Since the motorcycle had much less engine power than a Cessna 182, this was evidence that the concept would work.
The end result was that the disabled plane was successfully ferried in this manner, with permission from the FAA.  I don't recall the exact starting point of the ferry flight but I believe the distance was in the neighborhood of 60 miles.
The ending point was an untowered field and as best as I recall the starting point was as well.
Naturally, the tow line was released before the aircraft entered the landing pattern.
This all happened sometime between 1990 and 2005; I don't recall the date more accurately than that.
If your LSA did not have a tractor (nose-mounted) engine, you might have more of a challenge.
A qualified glider tow pilot will be needed to fly the towplane.


What is the best time to run runway friction tests? When is the best time to run runway friction tests?
And what is the optimum temperature to run them?

The friction will change over time due to temperature and moisture and other factors.
So, the best time to measure is shortly before a plane is about to land. In order to allow planning of alternatives, allow a longer time.


How is smoke detected in the cabin when flying without passengers? The Boeing website states that smoke detection devices are not present in the passenger cabin as the passengers/cabin crew are able to detect the smoke:

  A dedicated smoke detection system is not required in the occupied volumes of the main cabin due to the ability of passengers and the cabin crew to recognize smoke.

How would smoke be detected in the cabin when flying without passengers or cabin crew? As an example, this could be the case on a ferry flight where no one in the cabin may be present to detect smoke.

The threat for a cabin compartment smoke or fire comes from paying passengers & baggage.
On a ferry flight, you have neither, so the threat is greatly reduced or eliminated.
The FAA authorizes ferry permits for only 1 or a few  segments to get an aircraft to a facility where maintenance can be performed, these ferry permits take into account the risks involved and thus why no revenue cargo / passengers can be carried.


What factors affect the minimum time to go from point A to point B? I've created this trajectory for a small RC aircraft to go from 15m to 61m as quickly as possible (e.g. quickest time to get from point A to point B). I'm trying to perform a sanity check for why the aircraft would go to the lowest allowed altitude to maximize velocity before beginning it's climb. Can anyone provide an explanation for why this would be most time-efficient for this problem?
The reason that the aircraft does not fly lower than 5m is because I set 5m as the lowest possible constraint. If that constraint was not in place, it would try to fly at 0m.
Edit:
The reference listed for this type of problem is given as 'J. Betts. SOCS Release 6.5.0, 2007.'. This is an inappropriate place to ask for this, but I have tried searching for whatever this paper/journal this may be referencing and cannot find it. If anyone has any tips/tricks on how to actually find this source, please let me know

It looks to me like your airplane, starting with a very low velocity, is trying to climb a height of 46m (61m - 15m).

Because it has a low initial velocity, your basic choices are:

Start climbing immediately, demanding engine power both for velocity and climb rate, and climbing very slowly.
Fly level for a period of time to build up velocity, then begin the climb.
Use gravity and engine power together to get more velocity quickly, then begin climbing at a much faster rate.

The velocity you need to achieve is called $V_y$, or best rate of climb.
Based on the Yellow color on the main segment of the climb, it looks like this plane's $V_y$ is about 26 $m\over s$.

It looks like your software package chose #3.  While it makes intuitive sense, without the math behind it, I cannot tell you the details.


How can I go from a CPL to an A320 Rating? For example, I completed my CPL multi and have 300 flight hours, can I do a A320 type rating and work for an airline if they allowed my to work with 300 hours?

A U.S. pilot with a Commercial license can get a type rating by going through an appropriate course. It isn't cheap, but it can be done.

The benefit of having the type rating with only 300 hours is probably pretty slight, at least in the U.S.  Anybody hiring into the right seat of an A320 either has their own "ab initio" curriculum, or else they're probably looking for far more experience than that.  There may be a unique job out there that is looking for exactly this sort of applicant, but it seems hard to imagine.

You might be better off saving the money until you have a line on exactly what position you're after, and you're confident that they'd hire you with 300 hours (or whatever you have by then). Who knows -- you may find someplace that will be glad to hire you to fly something else, if you'll get the training on (whatever they fly) by going to get the type rating. Having the money available to spend on the needed type rating could be a lot more useful than have the 320 type at that point.


Are there any precision approaches that use only GNSS/LAAS? Is there any airport which has a precision instrument approach using only GNSS (augmented with LAAS) for guidance?

The FAA has an FAQ on GBAS (ground-based augmentation of GPS/GNSS). It says they no longer use the term LAAS, instead they now use GBAS to be consistent with ICAO terminology. A GBAS approach is called GLS on the approach charts.

The FAQ has information about where GBAS is used:

  Where are operational GBAS systems located?

  Currently, two U.S. locations have obtained operational approval for
  public GBAS use and support revenue airline traffic. These stations
  are located at Newark Liberty International Airport (EWR) and Houston
  George Bush Intercontinental Airport (IAH). Internationally, several
  airports have GBAS and support revenue operations (Bremen and
  Frankfurt, Germany; Sydney, Australia; Malaga, Spain; Zurich,
  Switzerland; and 15 Russian locations).

Newark (KEWR) has 5 GLS approaches, Houston (KIAH) has 6. I looked at a couple of the approach plates and they didn't require any additional equipment apart from the GBAS equipment itself. Note that GBAS is not the same as the 'typical' GPS/WAAS combination used for RNAV GPS approaches, and it requires different equipment:

  Can the same avionics be used for GBAS and WAAS?

  The GBAS and WAAS standards are different and initial avionics and
  integrations only supported one of the two capabilities. Emerging
  aircraft integrations can support both services (e.g. A350).


How do aircraft altimeters calculate altitudes accurately while airborne? While an aircraft is airborne, the local barometric pressure can change, causing an altimeter to no longer display the correct altitude. How are altimeters re-calibrated to display the correct altitude, or there are other methods to accomplish that?

Altimeters are calibrated to a standard atmosphere model (International Standard Atmosphere, ISA).

What the altimeter shows you is the vertical distance between the altitude equivalent to your current pressure (pressure altitude) and a reference "pressure altitude". The reference pressure altitude is set in pressure units (hPa or In. Hg) on the altimeter subscale. This is known as the "altimeter setting", set in the "altimeter setting window".

Image credit: FAA Pilots Handbook of Aeronautical Knowledge

Flying at lower altitudes (below "transition altitude"), the altimeter is set to airport/regional QNH, which is a pressure calculated so that if you were standing on the measurement point, the altimeter would indicate your exact elevation. At other altitudes, it would approximate altitude above mean sea level, although it would show incorrectly if temperature differed from ISA.

Above transition altitude, the altimeter is set to QNE, or standard pressure (1013.25 hPa, or 29.92 In. Hg). The altimeter will now only indicate correctly if both temperature and pressure are in accordance with ISA. You are now flying on "flight level" (where the FL is your QNE indication in hundreds of feet, ie 20,000 ft = FL200).

For the purpose of avoiding obstacles, both QNH and QNE have to be corrected using various methods, which are described in various manuals. (QNH for temperature, QNE for both temperature and pressure, both for other possible factors such as wind etc). For instance, this diagram shows three different aircraft, all flying the same pressure altitude, but with three different true altitudes:

Image credit: FAA Pilots Handbook of Aeronautical Knowledge

However, altitude is also used for the purpose of traffic separation, and for this purpose, neither QNH or QNE is corrected. This might sound counter-intuitive, but as long as your altimeter is showing the same error as any conflicting traffic, you can be safely separated, therefore: The altitude shown on the altimeter is not corrected at all (except by calibration for possible aerodynamic interference, such as compressibility, venturi-effects etc).

In technically sophisticated aircraft, barometric altitude input is used for vertical navigation. Since vertical navigation is concerned with the true altitude of the aircraft, the aircrafts Air Data Computer (ADC) will calculated a true altitude based on information available to it (either through sensors, or through pilot input). The true altitude is however, as stated, not shown on the pilots primary flight instruments.


Where can I find a collection of maximum range at maximum payload values for all aircraft types? The scope of my Master Thesis is the development of an assignment algorithm of aircraft types to routes with a given distance. As part of violation checks I'm validating the possible range of the AC type against the route distances.

As defined per payload-range diagram the max range of an aircraft type is not a static value but depends on the amount of payload desired. For a more realistic approach I'm looking for values of the max range at maximum payload of every aircraft type defined in ICAO Doc 8643.

However this value is not very easy to find out. Does anyone have an idea where to find a list of all (or at least all major aircraft types) max ranges at max payload of all aircraft types given in ICAO Doc 8643 grouped by the ICAO Designators (e.g. A332, B773, etc.)

Perhaps the DVB Bank report "An Overview of Commercial Jet Aircraft 2013 - 2014," contains the information you are looking for.

It contains a type description, performance data, world fleet data and engines for many aircraft types, as well as payload-range diagrams for each aircraft category.


Did Japan actually use any production aircraft with inverted gull wings during WW2? The anime film The Wind Rises presents a fictionalized account of Jiro Horikoshi and the development of the Mitsubishi A5M. Throughout most of the anime, Jiro visualizes the plane with this shape:

I recognized this shape from a production aircraft, but being rusty on my WW2 aviation knowledge, assumed it was the A6M Zero (the designation is never stated in the film). In reality, the production A5M and A6M had fairly straight wings, but the prototype A5M (which is what is depicted in the film) had inverted gull wings:

I then realized that the inverted-gull wings aircraft that I was thinking of was an American fighter, the somewhat similarly-shaped Vought F4U Corsair:

This got me curious on whether any production aircraft used by the IJN (or any branch of the Japanese military) during WW2 used inverted gull wings. From the photos and diagrams I can find, it looks like Japan stuck exclusively with straight wings, but some aircraft are depicted from a side view where it's very difficult to discern the exact shape of the wings.
Did Japan actually fly any production aircraft with inverted gull wings during WW2?

At least one - the Aichi B7A - although it saw little action, coming very late to the war.

The Aichi B7A Ryusei (愛知 流星艦上攻撃機 Aichi ryuusei-kanjou-kougeki-ki)
("Shooting Star", Allied reporting name "Grace") was a large and
powerful carrier-borne torpedo-dive bomber produced by Aichi Kokuki KK
for the Imperial Japanese Navy Air Service during the Second World
War. Built in only small numbers and deprived of the aircraft carriers
it was intended to operate from, the type had little chance to
distinguish itself in combat before the war ended in August 1945. (source)

 (source)
 (source)
The director of The Wind Rises Hayao Miyazaki may also be familiar with another Japanese gull-wing design, the Kawanishi E11K "Laura" flying-boat, which too saw service in WW2. However, its wing is not inverted.
 (source)


How many radio transmissions per hour occur on a given frequency over Europe and North Atlantic? For one of our research projects, we want to simulate a north atlantic flight from Frankfurt, Germany to the U.S.. To make it realistic, we are also simulating air traffic control - both instructions and clearances for the flight to be simulated as well as for all other flights on the same frequency. Now we were wondering, how "dense" is voice radio chatter over Europe (mainly Maastrict UAC and Scottish UAC) and over the North Atlantic (with CPDLC - Controller Pilot Data Link Communication in use)? In other words, how many transmissions per hour do pilots listen to in the given regions (approximately and in average)?

Please note, this question is not only about radio transmissions regarding the own flight, but transmissions from all flights on a given frequency that pilots listen to.

While this likely depends heavily on day and time, let's consider a typical weekday, departing Frankfurt around 10am local, so a time frame 1000Z - 1400Z for the above named regions would be of interest.

Can anyone, potentially a pilot regularly flying such a route, give some estimates?

It helps to check prior research in that field, for example, VOCALISE: Assessing the impact of data link technology on the R/T channel (2005).

  Quantitative aspects of pilot-controller communication are addressed in two en-route air traffic control studies: the VOCALISE study in a real operational environment (Graglia and al., 2005), and the EEC study in a simulation environment (Hering, 2001).

  The VOCALISE study shows that on average 324 speech acts between controllers and pilots were recorded per hour in an en-route sector, or about 5 per minute.

(Source: Eurocontrol)

So for the en-route portion, a single sector/frequency deals with about 5 transmissions per minute. Note that some of the transmissions would fall under miscommunication, such as:

  Incorrect read-backs
  Call-sign confusions
  Initiation failure
  Understanding failure
  Memory failure
  Information failure
  Omissions
  Redundancies

An example breakdown:

  [Out] of the incorrect read-backs, 30% are simple "say again" requests, and another 30% requests for repetition or confirmation of route information.

So that's another aspect to include in the simulation you'll be conducting.


Does a VNAV PTH descent need the Forecast Descent winds? If VNAV PTH, contrary to VNAV SPD, maintains a given path angle, depending on the CI chosen, and not a given Speed, then in my mind winds shouldn't affect it, since they would only cause the Vertical Speed to be adjusted accordingly in order to stay on that "fixed" path (since winds will alter the Ground Speed)
After all, VNAV PTH has a band of approx. +/- 12 kt (i.e. 24 kt in total) within which it does not "care" what your speed is. All it wants is to maintain the selected Path.
Hence my question: Does one need to fill in the Forecast Descent Winds for a VNAV PTH descent?
Though I can clearly see and understand how they will affect a VNAV SPD descent.
Because if your primary target is maintaining a given Indicated Airspeed, (be it Mach or IAS), then the winds definitely define where you are going to end up on the ground.

Yes, a VNAV PTH certainly needs descent winds so as to calculate and construct the most efficient flyable PATH. The PATH as we know. is built backwards from the landing RWY threshold to Top Of Descent (TOD).
Before I continue, I must say that sometimes managing VNAV PTH can become an unnecessarily complex task, if that's where you're coming from. We always have the alternative of lower levels of automation.
Flyability of the PATH means that the airplane should be on the FMC calculated 3 dimensional PATH  as well as the FMC calculated SPD at all times during descent, approach and landing. This depends on accurate depiction in the FMC of altitude and speed limitations, hopefully no changes to the lateral path, ie routing, and accurate wind data etc.
Small components of Head Wind or Tail Wind may not make it impossible to fly the PATH, but as the HW or TW component increases, it can make it very difficult to maintain and the SPD variations, especially in the upward direction and at altitude can be nerve-racking at times on certain types.
Try flying eastbound into TOKYO (Narita) on VNAV with 600+ kts of Ground Speed due 120+kts TW component without feeding the final cruise and descent wind data - guaranteed 'fun'n'games for the pilot and a possible violation. There's an 18,000 ft crossing restriction which, may become impossible to comply with depending on when the pilot catches on to the problem.
There is always recourse to the use of Speedbrakes if the airplane goes above the calculated profile, and Thrust if it goes below that profile. But the use of either of these indicates a deviation from the most efficient descent, and costs fuel.
In the ultimate analysis, @Stamatis Vellis, while one may not bother to put in any winds for  a 40 minute flight at FL 250 with light winds aloft, why willingly transgress the VNAV Speed Band (referred by you as +/- 12 kts), waiting for the FMC to automatically 'flip' from VNAV PTH to VNAV SPD.
VNAV PATH also represents fuel savings - my take is that when a facility exists, why not use it? 2 minutes spent on putting in effective wind forecasts, can make a more optimized, fuel efficient flight, more comfortable speeds, lower workload, more headspace for the pilots to monitor and make better tactical decisions ALL of which has direct safety impact.


Why is the A380's fuselage designed with a flat bottom? I want to know if there is some explanation for why the A380 bottom is flat instead of the oval shape, just near the wings.

There are 2 main reasons:

The wing spars run through that area. If you wanted to keep the wing spar within the oval cross-section, you'd have to install the wing much higher on the fuselage which means the wing spar goes through the passenger cabin.

Behind the wing spars, the landing gear is stored. The flat bottom provides more internal space.

Another image showing more detail of the structure:


Is training required under §61.55 to move from PIC to SIC? I am current as PIC in type on a jet requiring two crew members. I will be out of currency as PIC soon and my company wants me to move to SIC position when that happens.

Am I required to have training specified under 14 CFR 61.55 for SIC if I am already type rated in the aircraft?

No training needed.  If you are typed in the aircraft, none of the SIC type stuff applies (that is just an ICAO formality and is superseded by having a normal type rating).  As long as you meet the requirements to act as SIC (landing currency, company training currency, etc) you are good to transition to the right seat with no additional training.


Are there conventions on which side to travel on Victor airways - USA? I'm a low-time VFR pilot (100hrs) in the United States. I have not yet started IFR training (other than XC time building).

I understand the purposes and reasons why the Victor airways exist. I also understand the Victor airway widths are 8 NM minimum but widen when the VORs are further than 51 NM apart.

I regularly try to follow the Victor airways and VFR altitudes on VFR Cross Country flights, and do file VFR flight plans and use flight following. This makes it easier for me to communicate my position and seems it would be safer than just flying direct.

Question:

Is there a convention for a side of the "road" you should travel on in the USA?

My guess would be if a convention exists, it would be you should always travel on the right; this puts the red lights of the left wings of crossing traffic together, enforcing / encouraging avoid to the right; both A/C would make turns to the right, further expanding the horizontal gap between them. Right of way to the right, avoid to the right.

Background:

On a recent XC from KIXD to KSGF, I was traveling east at 5500' MSL and was directly over the radial, according to my GPS and my ODI. A west-bound crossing plane on VFR was at 6500' MSL and about 1 NM to the south of the airway. We both were using flight following and were alerted and there were no issues. But it made me pause to think, should I really be centered right on the radial? What if he were as well? Then there would be 0' horizontal separation, only 1000' vertical. And worse, if he were IFR at 6000' and right on the radial, that's even closer.

If you are flying IFR the FAA expects you to be on the centerline of the airway, as per the FAA's IFR flying manual

  to operate an aircraft within controlled airspace under IFR, pilots
  must either fly along the centerline when on a Federal airway or...

I can't find any references in the Airplane Flying Handbook to airways at all and keep in mind under VFR "see and avoid" is paramount but centerline is generally accepted. If you are flying with any kind of an autopilot/GPS unit thats where its going to put you.

Moving to your IFR example

  And worse, if he were IFR at 6000' and right on the radial, that's
  even closer.

500 is more than enough for the FAA's liking especially when one of those planes is flying under IFR.

  Most airways are eight nautical miles (14 kilometers) wide, and the
  airway flight levels keep aircraft separated by at least 500 vertical
  feet from aircraft on the flight level above and below when operating
  under VFR.

The reality is there is often even more separation since under VFR you are required to stay 500 below the cloud bases which are not always at round numbers you may often end up at the next lowest VFR cruising altitude

It is however, advised that if you are flying IFR but climbing on an airway in VFR conditions you execute gentle banks to look for traffic.


What is the benefit or motivation for having Class G airspace? I'm looking at the differences between Class E and Class G (AIM 3-2-6) airspace in the United States and I get that there are different flight condition requirements depending on AGL/MSL altitudes, but if you're outside a Mode C veil and around an untowered airport (So you don't need a transponder, don't need a radio), why not make everything Class E?

I think the answer came to me while writing this out...is it this simple?

Does Class G exist because for whatever reason (Radar services not available, technical reasons, etc.) ATC is unable to provide IFR separation services in that area, so it has to be deemed "uncontrolled?"

Is there some other reason why Class G exists besides being a catch-all?

  Class G airspace (uncontrolled) is that portion of
  airspace that has not been designated as Class A,
  Class B, Class C, Class D, or Class E airspace.

Like is there some benefit that you get when you're in Class G instead of Class E? The only thing I could think of is that the flight visibility is less than 3 miles but more than 1, it's daytime and the cloud deck is lower than 500 feet AGL (since you just need to be clear of clouds and 1 SM visibility), you could take off VFR in Class G and you couldn't take off in Class E. (However, you'd still have to be sure not to be engaged in Careless or reckless operation (14 CFR § 91.13).)

You can also fly Ifr without a clearance in G.

Remember that the entire purpose of airspace is to keep us from hitting airliners. It is not about keeping GA planes apart. When you look at wx mins that is clear. The FAA gives us the freedom to fly around in low vis so long as we stay out of the areas you'd find airliners.

-Robert CFII


Need help to clarify the terms "arrival", "departure", "approach", "terminal" and "transition" fix for US STAR and SIDS I find it a bit difficult to clarify, while consulting the US published STAR and SID published charts, which fixes are designated as arrival, departure, approach, terminal and transition.

Could somebody point out the aforementioned distinctions or any source that would help clarify these terms? I have gone through the FAA's Aeronautical Chart User's Guide but I was unable to discern the subtleties of each definition.

I am not an FAA controller or instrument rated but since you don't have an answer yet I will give it a shot.  If someone has a better answer please post:

Arrival:  IFR routes that start at radius about 30-50 NM from the airport.  This is where airplanes usually start their descent.  This can be controlled by en route or TRACON ATC.

Approach:  An IFR route that outlines a particular approach to the runway.  There are RNAV (GPS), VOR, and ILS approaches that are provided for an airport's runways.  You would file an approach during your IFR flight plan but could be modified by ATC as needed.  This is handled via ATC by approach control.

Terminal:  The area handled by a TRACON (for busy airports).

Departure:  Your IFR route filed when you depart from the runway.  This is handled via ATC by Departure.

Transition:  I am not so sure on this but I think this relates to going from arrival to approach.


What is the two-person cockpit rule, as of February 2020? In the comments to the accepted answer on this question, there is some conflicting information about the current regulations around the 2 person cockpit rule.

I was under the impression that there must be 2 people at all times after Germanwings Flight 9525.

What is the rule currently (Feb 2020) in both EU and the U.S for minimum number of people in the cockpit?

As for the EU, EASA has published SIB 2016-09 which states that: (emphasis mine)

  CAT.OP.MPA.210 of Regulation (EU) No 965/2012 stipulates that flight crew members required to be on duty in the flight crew compartment shall remain at the assigned station, unless absence is necessary for the performance of duties in connection with the operations or for physiological needs, provided at least one suitably qualified pilot remains at the controls of the aircraft at all times.

  In such cases, the Agency recommends operators to assess the safety and security risks associated with a flight crew member remaining alone in the flight crew compartment.
  This assessment should take the following elements into account:

  1) the operator’s psychological and security screening policy of flight crews;

  2) employment stability and turnover rate of flight crews;

  3) access to a support programme, providing psychological support and relief to flight crew when needed; and

  4) ability of the operator’s management system to mitigate psychological and social risks.

In other words, it is up to the individual airlines to decide if they want to implement a rule requiring two people in the cockpit at all time. It is not a legal requirement.


How would one define or explain the term "unloading the controls?" I've heard people say "unload the controls" or "unload the wing/propeller."

What does this mean exactly? It is usually followed by releasing back pressure on the elevators or starting/ending a turn.

When maneuvering the aircraft by deflecting the control surfaces with the stick, the wing with the downward aileron and the tail will generate additional lift, which increases the load on that wing (using the ailerons) and on the tailplane (using the elevator).

Unload the controls is a request to neutralize the pressure on the controls. Usually this means bringing the stick back to the center position, reducing the controls surface deflection, the amount of lift generated, and therefore reducing the aerodynamic load on the wings and tailplane.


When and why was runway 07/25 at Kai Tak removed? Wikipedia states that Kai Tak Airport in Hong Kong originally had two runways, both built under Japanese occupation during World War II:

  ... In 1942, the Japanese army expanded Kai Tak, using many Allied prisoner-of-war (POW) labourers,[9] building two concrete runways, 13/31 and 07/25.

However, by the time Kai Tak was closed in 1998, only one runway (the famous 13/31) remained.  I can find no mention of when runway 07/25 was closed, or why; can someone help answer those questions?

The two original short runways (shown above) were actually abandoned c. 1955 in favor of a brand new longer runway built into the bay (completed 1958) to accommodate the new jetliner (the 13/31 you know).

  The year also saw the start of work on a $110,000,000 project to revolutionize Kai Tak Airport by the construction of a 7,200-ft runway on an artificial promontory reclaimed from the sea and projecting out into the waters of Kowloon Bay. In danger of being knocked off the international airline map by reason of its airport being too small and dangerous for the Comet and the larger conventional airliners, Hong Kong has now taken steps to keep itself firmly on the map. The airport project, when completed in 1958, will provide, for the first time since aviation started in the Colony, facilities for day and night operation all the year round.

A note on the design of runways: Two intersecting runways are usually treated as one, as both can't be used simultaneously unless they're sufficiently long and a procedure like LAHSO is used. Kai Tak started with 2 to cover the compass as much as possible, since early on the designers didn't have wind data. It was typical of that era to build 3 runways 60° apart, then later on expand the most useful, and abandon the rest.

Source: https://gwulo.com/kai-tak-airport-history


What in-flight weather info is available to commercial pilots? This question was asked yesterday about sources of wx info. The answers focused on sources for pre-flight planning. As weather changes constantly pilots need current wx info en route, especially on long flights.

The wx radar aircraft are equipped with can show what they are approaching for the next several miles, but often pilots need to know what is in their path much further ahead than what onboard radar can show.

This question asks about in-flight wx info via cellular connection. The answers all allude to the unreliability and possible illegality of cellular use. However, in the comments several people suggested sources available through satellite and FIS-B.

I was reading this blog post relating to the recent Delta flight which suffered severe hail damage after flying into a storm. The author decries the lack of weather info sources available to commercial pilots in-flight. He says, "a pilot flying a single engine Cessna 172 can have significantly more weather information available to them in the cockpit than the crew of this A320 had." The author of the blog post is advocating for airlines to provide this info.

With many airliners now equipped with wifi it seems a pilot could have access to any number of ground-based NEXRAD radar services through a tablet or their EFB. What is there preventing commercial pilots from using these services? Is there an FAA rule that prohibits this or do airlines have rules as to where they can get their weather info?

Air Traffic Control

Air Traffic Control (ATC) are often a major source of weather information for pilots. Modern ATC radars often overlay weather radar over the screen so ATC can assist pilots in avoiding weather. In terminal areas ATC may be equipped with additional systems such as terminal doppler weather radar (TDWR) or low-level windshear alert system (LLWAS). If able, ATC will impart any weather information they have to pilots to assist them in choosing the safest course. That's an ideal scenario of course and sometimes ATC isn't helpful.

En Route Flight Advisory Service (EFAS or Flight Watch)

  A service specifically designed to provide timely en route
  weather information upon pilot request is known as the en
  route flight advisory service (EFAS), or Flight Watch. EFAS
  provides a pilot with weather advisories tailored to the type
  of flight, route, and cruising altitude. EFAS can be one of
  the best sources for current weather information along the
  route of flight.

  A pilot can usually contact an EFAS specialist from 6 a.m. to 10
  p.m. anywhere in the conterminous United States and Puerto
  Rico. The common EFAS frequency, 122.0 MHz, is established
  for pilots of aircraft flying between 5,000 feet above ground
  level (AGL) and 17,500 feet mean sea level (MSL).

Hazardous Inflight Weather Advisory (HIWAS)

  Hazardous Inflight Weather Advisory (HIWAS) is a national
  program for broadcasting hazardous weather information
  continuously over selected navigation aids (NAVAIDs). The
  broadcasts include advisories such as AIRMETS, SIGMETS,
  convective SIGMETS, and urgent PIREPs. These broadcasts
  are only a summary of the information, and pilots should
  contact a FSS or EFAS for detailed information. NAVAIDs
  that have HIWAS capability are depicted on sectional charts
  with an “H” in the upper right corner of the identification
  box.

XM

Many modern avionics systems receive NEXRAD over XM as well as a myriad of other weather sources. Avionics suites such as the Garmin G1000 give pilots access to NEXRAD overlay over a map as well as a visual display of METARs, TAFs, FDs, PIREPs and many other weather information sources. There were a lot of acronyms there, but they can all be referenced in the two references provided at the bottom of this answer.

On-board Radar

Many aircraft are equipped with radar on-board. This provides a major step up from NEXRAD for making specific choices. Some pilots may disagree, but I view NEXRAD as a way to make "overview" choices about weather. NEXRAD is often too far delayed or affected by errors to make fine-grain choices. On-board radar can be directed at the airplane's altitude and provides an immediate picture of what's happening.

I also read the article from ForeFlight about the Airbus that got into hail. It's true that many general aviation aircraft have more in the cockpit that airliners. I'm not sure if airline pilots are allowed to use additional sources from things like ADS-B receivers they bring with them, but my guess is that while it's probably not forbidden, it's a risk to the pilot. If a situation arose where a pilot made a decision based on information from an unofficial source and it lead to a bad result it could be detrimental for the pilot and the airline. Most pilots probably stick to their official sources.

For pilots flying under the FAA, two good sources for the answer are the Pilot's Handbook of Aeronautical Knowledge (PHAK) Chapter 13 and AC 00-45G. Chapter 13 of the PHAK is dedicated to aviation weather services, many of chich are available in flight. AC 00-45G is dedicated to the same, it just tends to be updated a little more often and goes into greater detail.

Generally speaking though I have found that FAA materials haven't done the best job in keeping up with the fast pace of technology and its modernizing effects on avionics. Then again, the modern technologies are usually repackaging existing weather services and providing them in a better interface.


What are the differences between FANS A, B, and C? Is FANS C commissioned? For the Future Air Navigation System, what are the differences between FANS A, B, and C? Is FANS C commissioned?

A, B, and C are the names used by Airbus. As a short summary:

If you want text communication with ATC (CPDLC), you need FANS A in USA/oceanic, and FANS B or C in Europe.
If you want position/trajectory reporting at set intervals (ADS-C) in continental Europe, then you need FANS C (still being tested).

  (Own work)

See the Airbus slide below for more:

  Source: Airbus via icao.int (PDF)

Operational demonstration of FANS C started a year ago in Europe.

Related:

How does ADS-C and FMS relate to FANS?
What's the relationship between FANS and CPDLC?

Acronyms list:

  ► A623: ARINC protocol defining a set of data
  link applications (DCL, OCL, D-ATIS)
  ► ACARS: Aircraft Communication and
  Addressing Reporting System
  ► ACR: Avionics Communication Router
  ► ADS-C: Automatic Dependent Surveillance -
  Contract
  ► ADS-B: Automatic Dependent Surveillance -
  Broadcast
  ► AFN: ATS Facility Notification
  ► AOC: Airline Operations Control
  ► ATN: Aeronautical Telecommunication
  Network
  ► ATSU: Air Traffic Service Unit
  ► CM: Context Management
  ► CPDLC: Controller Pilot Data Link
  Communication
  ► CVR: Cockpit Voice Recorder
  ► D-ATIS: Digital ATIS
  ► DCL: Departure Clearance
  ► DR: Data link Recording
  ► FANS: Future Air Navigation System
  ► FMS: Flight Management System
  ► HFDL: HF Data Link
  ► HFDR: HF Data Radio
  ► IMA: Integrated Modular Avionics
  ► LRU: Line Replaceable Unit
  ► OCL: Oceanic Clearance
  ► RMP: Radio Management Panel
  ► SDU: Satellite Data Unit
  ► VDL: VHF Data Link
  ► VDR: VHF Data Radio


What is the range of frequencies of vibration in a helicopter due to the main rotor alone? Vibration in helicopter can be caused by many different reasons. I am interested to know what is the range of frequencies of vibration due to the main rotor alone?

I understand that it would depend on the helicopter type. So any reference to such analysis would be appreciated.

The vibration from the main rotor (and of the tail rotor) are harmonics of the Blade Passing Frequency: number of blades times rotational velocity. This site contains some data on the Blade Passing Frequencies of some helicopter types, for analysis purposes for military helicopters which must comply with MIL-STD-810F.
Image source

MIL-STD-810F, Method 514.5, paragraphs 2.2.6 and 2.3.3 are concerned with the vibration levels that helicopter components and cargo must withstand.
The helicopter vibration environment is a combination of many sinusoidal components due to the main rotor, tail rotor, gearbox, and engine.

Image source
Since the vibrations are also imparted on the surrounding air and then onto the fuselage, acoustic measurements are a good indication of the mechanical vibrations as well. Above graph shows acoustic measurements of seven Hueys flying by, and shows harmonics at intervals of 12 Hz. From the referenced article:

The first notable peak occurs at 24.0 Hz. A series of harmonics occur at 12 Hz intervals thereafter. These are the blade passing frequencies of the main rotor.
The main rotor blade passing frequency is: 5.40 Hz x 2 blades = 10.8 Hz
The Doppler shift increases the apparent blade passing frequency to 12 Hz. The theoretical speed of the helicopters was 76 mph based on this shift.

An interesting factoid is that the highest peak is not caused by the main rotor but by the tail rotor: the one at 123 Hz.
The highest main rotor vibration peak occurs at 60 Hz, five times the main rotor Blade Passing Frequency. There are still noticeable 12 Hz peaks at up to 300 Hz sound frequency = 270 Hz frame vibration frequency.

EDIT

This presentation shows vibration measurements taken off of an unnamed helicopter. The rotor frequency is detectable as a small peak, the blade frequencies are much more dominant.


What type of fuel is used in helicopters? What type of fuel is used in helicopters?

Do they use Aviation Turbine Fuel (jet fuel), which is used widely in commercial airlines?

Also, where would be the fuel tank located in a helicopter?

It depends on the engine. A piston engine will use avgas (aviation gasoline) or diesel (or Jet-A for availability reasons) depending on whether the engine is a diesel engine (which can burn jet fuel), while a turbine engine will use jet fuel. Essentially whatever the engine is rated to burn.

The fuel tank is somewhere in the fuselage near the center of the rotor. This to avoid the center of gravity shifting with the fuel level.