Who authorizes low visibility takeoff operations for airlines, and what is required? A previous question pondered the legality and safety of low visibility Part 91 takeoffs. I am wondering about the requirements for low visibility takeoff for commercial airline operators (e.g. Part-121 scheduled operations). I know of authorizations for operators down to 600 RVR (though I believe I recall 300 RVR for one carrier out of DEN), and various requirements for other increments below standard takeoff minima.

My question is:

Which RVR are authorized and what ground equipment requirements need to be met to use them?
What authorizes (regulation? op spec?) these reduced visibility operations?

The Part 121 regulation that governs low visibility takeoffs are specified in 14 CFR 121.651.  It references company OpSpecs and 91.175 and Part 97:

"Standard" takeoff minimums are specified in 14 CFR 91.175 and would be the highest of:

Non-standard takeoff minimums specified on the airport charts (FAR 97)
For aircraft, other than helicopters, having two engines or less — 1 statute mile visibility.
For aircraft having more than two engines — 1⁄2 statute mile visibility.
For helicopters — 1⁄2 statute mile visibility.

OpSpec C056 is issued to all 121 carriers, and basically just spells out the "standard" takeoff minimums that I listed above, and specifies that RVR must be used if it is available on the runway.

OpSpec C078 is normally issued and allows taking off with lower than standard visibility as long as the airport doesn't already have published higher than standard takeoff minimums.  This is a fairly involved OpSpec with several optional paragraphs, and operators may be approved for takeoff operations down to and including 300 RVR.  For those not familiar with the term, RVR (Runway Visual Range) is the distance that a pilot can see down the runway, measured by automatic equipment,  and is measured in feet in the US.

It offers approvals for the following visibilities:

1/4 SM / RVR 1600:

Touchdown zone RVR (or mid RVR if touchdown zone is inop) is controlling:
Requires "runway markings or runway lighting provide pilots with adequate visual reference to continuously identify the takeoff surface and maintain directional control throughout the takeoff run." (Basically as long as the pilot feels comfortable, but specifically mentions HIRL, CL, and RCLM as okay.)

RVR 1000 (optional)

Touchdown zone RVR and rollout RVR (A mid-RVR report may be substituted for either if they are inop, but still must have two systems) are both controlling
Requires Runway Centerline Lights (CL)

RVR 500 (optional)

Touchdown zone RVR, mid RVR, and rollout RVR are all controlling (one may be inop)
Requires Operative runway centerline lights (CL)
Requires Runway centerline markings (RCLM)

RVR 300 (optional)

Requires a takeoff guidance system
Requires operative high intensity runway lights (HIRL)
Requires operative runway centerline lights (CL)
Requires serviceable runway centerline markings (RCLM)
Front course guidance from the localizer (if applicable to the system used)
Crosswind less than 10 knots
Touchdown zone RVR, mid RVR, and rollout RVR are all controlling (one may be inop)
Requires special training requirements for both the PIC and SIC
Taxiways with operative taxiway centerline lighting must be available

Regulations/Sample OpSpecs

  §121.651 Takeoff and landing weather minimums: IFR: All certificate
  holders.

  (a) Notwithstanding any clearance from ATC, no pilot may begin a
  takeoff in an airplane under IFR when the weather conditions reported
  by the U.S. National Weather Service, a source approved by that
  Service, or a source approved by the Administrator, are less than
  those specified in—

  (1) The certificate holder's operations specifications; or

  (2) Parts 91 and 97 of this chapter, if the certificate holder's
  operations specifications do not specify takeoff minimums for the
  airport.

  §91.175 Takeoff and landing under IFR.

  ...

  (f) Civil airport takeoff minimums. This paragraph applies to persons
  operating an aircraft under part 121, 125, 129, or 135 of this
  chapter.

  (1) Unless otherwise authorized by the FAA, no pilot may takeoff from
  a civil airport under IFR unless the weather conditions at time of
  takeoff are at or above the weather minimums for IFR takeoff
  prescribed for that airport under part 97 of this chapter.

  (2) If takeoff weather minimums are not prescribed under part 97 of
  this chapter for a particular airport, the following weather minimums
  apply to takeoffs under IFR:

  (i) For aircraft, other than helicopters, having two engines or less—1
  statute mile visibility.

  (ii) For aircraft having more than two engines—1⁄2 statute mile
  visibility.

  (iii) For helicopters—1⁄2 statute mile visibility.

  C056, IFR Takeoff Minimums, Part 121 Airplane Operations - All
  Airports.

  a. Standard takeoff minimums are defined as 1 statute mile visibility
  or RVR 5000 for airplanes having 2 engines or less and ½ statute mile
  visibility or RVR 2400 for airplanes having more than 2 engines.

  b. RVR reports, when available for a particular runway, shall be used
  for all takeoff operations on that runway. All takeoff operations,
  based on RVR, must use RVR reports from the locations along the runway
  specified in this paragraph.

  c. When a takeoff minimum is not published, the certificate holder may
  use the applicable standard takeoff minimum and any lower than
  standard takeoff minimums authorized by these operations
  specifications. When standard takeoff minimums or greater are used,
  the Touchdown Zone RVR report, if available, is controlling.

  d. When a published takeoff minimum is greater than the applicable
  standard takeoff minimum and an alternate procedure (such as a minimum
  climb gradient compatible with aircraft capabilities) is not
  prescribed, the certificate holder shall not use a takeoff minimum
  lower than the published minimum. The Touchdown Zone RVR report, if
  available, is controlling.

  C078, IFR Lower Than Standard Takeoff Minimums, 14 CFR Part 121 Airplane Operations - All Airports.

  Standard takeoff minimums are authorized in operations specification
  paragraph C056. The certificate holder is authorized to use lower than
  standard takeoff minimums in accordance with the limitations and
  provisions of this operations specification as follows.

  a. Runway visual range (RVR) reports, when available for a particular
  runway, shall be used for all takeoff operations on that runway. All
  takeoff operations, based on RVR, must use RVR reports from the
  locations along the runway specified in this paragraph.

  b. When takeoff minimums are equal to or less than the applicable
  standard takeoff minimum, the certificate holder is authorized to use
  the lower than standard takeoff minimums described below:

  (1) Visibility or runway visual value (RVV) ¼ statute mile or
  touchdown zone RVR 1600, provided at least one of the following visual
  aids is available. The touchdown zone RVR report, if available, is
  controlling. The mid RVR report may be substituted for the touchdown
  zone RVR report if the touchdown zone RVR report is not available.

  (a) Operative high intensity runway lights (HIRL).

  (b) Operative runway centerline lights (CL).

  (c) Serviceable runway centerline marking (RCLM).

  (d) In circumstances when none of the above visual aids are available,
  visibility or RVV ¼ statute mile may still be used, provided other
  runway markings or runway lighting provide pilots with adequate visual
  reference to continuously identify the takeoff surface and maintain
  directional control throughout the takeoff run.

  [NOTE: If an operator is not authorized RVR 1000 the POI will not
  select RVR 1000 in the OPSS. If the OPSS is not available the POI
  should delete subparagraph b(2), b(3), & b(4) from the word
  boilerplate.]

  (2) Touchdown zone RVR 1000 (beginning of takeoff run) and rollout RVR
  1000, provided all of the following visual aids and RVR equipment are
  available.

  (a) Operative runway centerline lights (CL).

  (b) Two operative RVR reporting systems serving the runway to be used,
  both of which are required and controlling. A mid-RVR report may be
  substituted for either a touchdown zone RVR report if a touchdown zone
  report is not available or a rollout RVR report if a rollout RVR
  report is not available.

  [NOTE: If an operator is not authorized RVR 500 the POI will not
  select RVR 500 in the OPSS. If the OPSS is not available the POI
  should delete subparagraph b(3), & b(4) from the word boilerplate.]

  (3) Touchdown zone RVR 500 (beginning of takeoff run), mid RVR 500,
  and rollout RVR 500, provided all of the following visual aids and RVR
  equipment are available.

  (a) Operative runway centerline lights (CL).

  (b) Runway centerline markings (RCLM).

  (c) Operative touchdown zone and rollout RVR reporting systems serving
  the runway to be used, both of which are controlling, or three RVR
  reporting systems serving the runway to be used, all of which are
  controlling. However, if one of the three RVR reporting systems has
  failed, a takeoff is authorized, provided the remaining two RVR values
  are at or above the appropriate takeoff minimum as listed in this
  subparagraph.

  (4) At foreign airports which have runway lighting systems equivalent
  to U.S. standards, takeoff is authorized with a reported touchdown
  zone RVR of 150 meters, mid RVR of 150 meters, and rollout RVR of 150
  meters. At those airports where it has been determined that the runway
  lighting system is not equivalent to U.S. standards, the minimums in
  subparagraphs a(1) or (2), as appropriate, apply.

  c. Takeoff Guidance System, If Applicable. If the certificate holder
  is authorized to use takeoff minimums based upon the use of takeoff
  guidance systems, the minimums will be specified for the aircraft
  listed in the Table 1 below. The certificate holder shall conduct no
  other takeoffs using these takeoff minimums. If subparagraph c is not
  authorized, N/A will be annotated in each of the columns in the table.

  (1) Special provisions and limitations.

  (a) Operative high intensity runway lights (HIRL).

  (b) Operative runway centerline lights (CL).

  (c) Serviceable runway centerline markings (RCLM).

  (d) Front course guidance from the localizer must be available and
  used (if applicable to guidance systems used).

  (e) The reported crosswind component shall not exceed 10 knots.

  (f) Operative touchdown zone, and rollout RVR reporting systems
  serving the runway to be used, both of which are controlling, or three
  RVR reporting systems serving the runway to be used, all of which are
  controlling. However, if one of the three RVR reporting systems has
  failed, a takeoff is authorized, provided the remaining two RVR values
  are at or above the appropriate takeoff minimum as listed in this
  subparagraph.

  (g) The pilot-in-command and the second-in-command have completed the
  certificate holders approved training program for these operations.

  (h) All operations using these minimums shall be conducted to runways
  which provide direct access to taxi routings which are equipped with
  operative taxiway centerline lighting which meets U.S. or ICAO
  criteria for CAT III operations; or other taxiway guidance systems
  approved for these operations.

  (2) The certificate holder is authorized to use the following takeoff
  minimums for the airplanes listed below.

  Table 1 (N/A = Not Authorized) Airplane M/M/S Lowest Authorized RVR
  Required Takeoff Guidance System

  [NOTE: If an operator is not authorized pilot assessment the POI will
  not select this statement in the OPSS. If the OPSS is not available
  the POI should delete subparagraph d in its entirety from the word
  boilerplate.]

  d. Pilot Assessment of RVR for Takeoff (if applicable). In
  circumstances when the touchdown zone RVR reporting system has failed,
  is inaccurate, or is not available, the certificate holder is
  authorized to substitute pilot assessment of equivalent RVR for any
  touchdown zone RVR report required by this operations specification
  paragraph provided that:

  (1) The pilot has completed the FAA-approved training program for
  visibility assessment in lieu of RVR, and

  (2) Runway markings or runway lighting is available to provide
  adequate visual reference for the assessment.


What is the relationship between "automatic flight control system AFCS", "autopilot", "flight director" and "flight management system FMS"? I'm studying aircraft maintenance. I looked in my books and searched the web but couldn't make a big picture of the concept of autopilot.

Specifically what is its relation to modern systems like FMS.
Is the AFCS an independent system or does it take orders from the FMS?
What are AFCS subsystems?
Is the flight director the old version of FMS?

Since you are studying maintenance, I would suggest you obtain a copy of ATA iSpec 2200, Information Standards for Aviation Maintenance ATA Standard Numbering System.  Most large aircraft manufacturers and airlines use the ATA Standard Numbering System in organizing their maintenance documentation.

To your specific question, the ATA spec lists the following:

The FMS is the primary tool for managing the navigation.  It is part of the larger Navigation system which includes the aircraft attitude, air data, and positioning sensors. The FMS supports flight planning (path definition) and integrated position determination.

  Chapter 34 NAVIGATION, section 60 Flight Management Computing.

  That portion of the system which combines navigational data to compute
  or manage the aircraft's geographical position or theoretical flight
  path. Includes items such as course computers, flight management
  computers, performance data computers, and associated control display
  units, warning annunciators, etc.

The FM function outputs a desired path and guidance data to the displays and AFCS. The FMS is one source of path and target (altitude and or speed) data for the AFCS. The other input source is by crew input via the Mode Control Panel (MCP).

The AFCS is functionally independent from the FMS and primary flight control system (FCS), though it is sometimes physically integrated with one or the other or both.

The AFCS has two major components, autopilot and auto throttle. Autopilot includes the Flight Director.

  Chapter 22 AUTO FLIGHT, section 10 Autopilot

  That portion of the system that uses radio/radar signals, directional
  and vertical references, air data pitotstatic, computed flight path
  data, or manually induced inputs to the system to automatically
  control the flight path of the aircraft through adjustment to the
  pitch/roll/yaw axis or wing lift characteristics and provide visual
  cues for flight path guidance, i.e.: Integrated Flight Director. This
  includes power source devices, interlocking devices and amplifying,
  computing, integrating, controlling, actuating, indicating and warning
  devices such as computers, servos, control panels, indicators, warning
  lights, etc.

and

  Chapter 22 AUTO FLIGHT, section 30 Auto Throttle

  That portion of the system that automatically controls the position of
  the throttles to properly manage engine power during all phases of
  flight/attitude. This includes engaging, sensing, computing,
  amplifying, controlling, actuating and warning devices such as
  amplifiers, computers, servos, limit switches, clutches, gear boxes,
  warning lights, etc.

The AFSC computes the necessary control inputs to fly the aircraft along the defined path and meet targets.  It provides control inputs into the flight controls (ATA Chapter 27) or in the case of the Flight Director, it generates a display that directs the pilot to make the needed control inputs.

This steering will steer the aircraft to the path defined by the FMC, or it can steer to a simple path entered by the pilot directly into the AFCS via the MCP.  In older aircraft, the autopilot steers by using a series of special actuators to manipulate the controls. In modern fly-by-wire aircraft, it provides input directly to the FCS as the FCS already has the necessary actuators.

Auto Throttle provides throttle adjustments to meet speed targets from the FMC or MCP.

By the ATA standard, the FMS, AFCS, and FCS are three distinct systems. As noted above, modern fly-by-wire systems are beginning to blur the boundaries.  Without the need for separate actuators for the AFCS, it just becomes software much of which is getting merged with the primary FCS.


How does ATC control / separate Airbus Industrie test flights? Airbus is testing a A321 (D-AVXA, flight AIB97XA) around Toulouse this morning. The test is at low altitude, with many speed and altitude changes, including touch and go (maybe rolling slowly on the runway):

Source: FlightRadar24.

This path crosses other commercial routes / VFR aircraft, and it seems unlikely altitude, speed or even position can be anticipated all the time, but could be determined only while in flight.

All these constraints surely mean a specific treatment from ATC. How does ATC control and coordinate this flight with other aircraft? Toulouse Blagnac (LFBO) is open to commercial flights, and this test flight was within or close to Toulouse TMA.

They will be in contact with ATC at all times and ATC can issue a clearance to operate within a defined area or within a specific flight level range, keeping other aircraft out of that area, e.g.

  APP: AIB97XA, cleared for turns and flight level changes in 20NM radius around ABCDE intersection, between FL70 and FL145 at your discretion.

or a bit more standard phraseology:

  APP: AIB97XA, cleared for turns and flight level changes in 20NM radius around ABCDE intersection and maintain block FL70 until FL145.

From what is visible in the French AIP, the TMA airspace of Toulouse has airspace classes D and C from different altitudes up to FL145, also in the area where your mentioned flight happened.

(Source: German NfL 1-251-14 Verfahren Sprechfunk / P. 47)


What is the difference between centre of pressure, aerodynamic centre and neutral point? I have just started learning some aerospace concepts, and I am not able to understand the difference between the three terms centre of pressure, aerodynamic centre and neutral point. What are their functional differences?

What would be an example that distinguishes these three?

Any body moving in a fluid experiences pressure forces over its surface. The concepts of center of pressure, aerodynamics center and neutral point are useful in understanding the effects of these forces. Let's take an airfoil moving in air with subsonic flow attached to the body.

Center of Pressure The center of pressure is the point where the total sum of a pressure field acts on a body. In aerospace, this is the point on the airfoil (or wing) where the resultant vector (of lift and drag) acts.

Source: avstop.com

As the airfoil angle of attack changes, the pressure field changes. Due to this, the center of pressure changes with variation in the angle of attack. In the airplane's normal range of flight attitudes, if the angle of attack is increased, the center of pressure moves forward; and if decreased, it moves rearward.

Source: www.flightlearnings.com

As the center of gravity (the point where the weight of the body acts) is fixed, this movement of center of pressure affects the  stability of the aircraft.

Aerodynamic Center The resultant (or the pressure forces) also cause a moment on the airfoil. As the angle of attack increases, the pitching moment at a point (for example, the center of gravity) also changes. However, the pitching moment remains constant at a particular point, which is called the aerodynamic center.

Source: www.theairlinepilots.com

For symmetric airfoils in subsonic flight the aerodynamic center is located approximately 25% of the chord from the leading edge of the airfoil. This point is described as the quarter-chord point.

Thus the aerodynamic center does not change with variation in angle of attack. Due to this, the aerodynamic center, rather than the center of pressure is used in the analysis of longitudinal stability.

Neutral Point Consider the whole aircraft. The lift of the wing acting through the center of pressure is in front of the center of gravity of the aircraft. This causes a destabilizing motion (increase in lift to increase in angle of attack causes a nose up moment, further increasing angle of attack). This is counteracted by the moment produced by the lift of the horizontal stabilizer (which is a small wing), acting behind the center of gravity.

"AirStability" by User_A1 - SVG derivative of Public Domain work by G J Vigurs. Licensed under GFDL via Commons.

As the center of gravity is moved forward, the stability of the aircraft increases (as the main wing lift arm is reduced) and the aircraft is statically stable.

Source: quest.arc.nasa.gov

As the center of gravity is moved aft, the main wing lift moment arm increases and the aircraft stability decreases. The aircraft is said to be statically unstable.

Source: quest.arc.nasa.gov

As the aircraft is stable when center of gravity is in the nose and unstable when center of gravity is in the tail, there is a position in the middle where the aircraft is neither stable nor unstable i.e the stability is neutral. This point is called the neutral point. The neutral point is fixed for a particular aerodynamic configuration of the aircraft.

Source: quest.arc.nasa.gov

Thus,

Center of pressure of an aircraft is the point where the Lift acts.
Aerodynamic center is the point in the wing where the pitching moments are constant.
The neutral point is where the center of gravity of the aircraft is neutrally stable


Was this flight a fuel emergency? Yesterday I flew from San Diego to Boston in a commercial 737 operated by Alaska Airlines. Before landing we spent almost an hour circling. When we finally landed, many passengers were surprised to learn that we were not in Boston; we were still 90 miles / 150 km away.

The flight attendants told us the pilots had been too busy to announce the diversion. When the captain finally made an announcement on the ground, he said we had been redirected because the wait for Boston was 60 minutes and "we only had about 10 minutes of fuel left."

The cause was snow in Boston. Many flights were cancelled. However, visibility was excellent where we were and the flight was smooth. So I was surprised that we were diverted.

According to flightaware, we started circling at approximately 4pm; we were diverted at 4:48pm and landed at BDL at 5:03pm. Our scheduled arrival time was 5:06pm. (We departed on time.)

Below is the flight path (source).

I was hoping that some people more knowledgeable than myself could help me better understand what was going on.

Does "10 minutes of fuel left" mean 10 minutes until empty or 10 minutes until it becomes urgent? I find it hard to believe that there was so little reserve fuel, especially given that we were in the air for the scheduled amount of time.
Would this situation count as a fuel emergency? Was it comparable to this incident?
How low do commercial jets normally go fuel wise? In particular, how common is it to have 10 minutes of fuel left when landing?
Can I find out more information about my flight online? I only know of flightaware. Is it possible to find ATC radio recordings?

There appears to be no emergency. The flight was diverted at 16:58 EST and landed at Bradley International Airport at 17:03 EST. The same flight on 6th Feb landed at Boston at 16:46 EST. So basically, the flight was in the air only for an extra 15 minutes, compared to the scheduled time.
According to § 121.639 Fuel supply: All domestic operations.:

No person may dispatch or take off an airplane unless it has enough fuel—
(a) To fly to the airport to which it is dispatched;
(b) Thereafter, to fly to and land at the most distant alternate airport (where required) for the airport to which dispatched; and
(c) Thereafter, to fly for 45 minutes at normal cruising fuel consumption

So basically, the pilot diverted because the holding time was another 60 minutes and that would've eaten into fuel reserves.

I think the captain meant that the aircraft had only 10 minutes of fuel till he had to dip into reserves (or fly the alternate- it depends) and diverted because of the 60 minute waiting time. He could've been more clear though.

The pilot would've declared a fuel emergency if there was one. So, I think there was none.

Its quite uncommon for aircraft to land on 10 minutes of reserve fuel, though it has happened. In fact, some aircraft have run out of fuel.

You can find details about the ATC in liveatc's audio archives.


Does anyone know an equation relating wingspan to gliding distance for a glider? I found this equation online but it is not from a reputable source and has no derivation. Could anyone help me by deriving this equation or even verifying its accuracy? I would love to cite and use this equation in my assignment so urgent help would be most appreciated.

Your mystery equation is
$$\text{Distance} = \text{Height}\cdot0.5\cdot\sqrt{\pi\cdot e\cdot\frac{b^2}{f}}$$
Since the flight distance is the product of the glide ratio (or lift-to-drag ratio) L/D and height, the equation can be written like this:
$$\frac{L}{D} = \frac{c_L}{c_D} = 0.5\cdot\sqrt{\pi\cdot e\cdot\frac{b^2}{f}}$$
if we use dimensionless coefficients instead of the dimensionful forces. Now that does look familiar, right? Only something seems to be missing. And that drag area $f$ should be the wing area.

Now you asked for the derivation, and I've done that only with wind in this answer, so let's do it for the simpler case of a glider and without wind right here. You start with the question: What polar point gives the best distance for a given height? Or, in other words, when does the lift-to-drag ratio reach its optimum? To get anywhere, you need a simple equation for the lift-to-drag ratio, so I recommend to start with the equation for the drag polar
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\left(c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)$$
The terms inside the big bracket are the sum of the parasitic and the induced drag coefficient and the term in front of the bracket is the product of dynamic pressure and wing area. It is needed to turn the coefficients into a force. The symbols are:
$\kern{5mm} \rho\:\:\:\:\:$ air density
$\kern{5mm} v\:\:\:\:\:$ velocity
$\kern{5mm} S\:\:\:\:\:$ wing surface area
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} c_L \:\:\:$  lift coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's Oswald factor, normally between 0.8 and 1.0

Since lift should be constant over speed for a glider, the optimum lift-to-drag ratio is when drag reaches a minimum. We express the lift coefficient by what it stands for and differentiate drag with respect to speed:
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\ c_{D0}+\frac{(m\cdot g)^2}{\frac{\rho\cdot v^2}{2}\cdot S\cdot\pi\cdot AR\cdot\epsilon}$$
$$\Rightarrow\:\:\frac{dD}{dv} = \frac{2\cdot \rho\cdot v}{2}\cdot S\cdot c_{D0} - \frac{2}{v^3}\cdot\frac{2\cdot(m\cdot g)^2}{\rho\cdot S\cdot\pi\cdot AR\cdot\epsilon}$$

Drag should reach its minimum when the derivative equals zero. We try to isolate the zero lift drag by dividing the equation by all what is collected around it:
$$0 = c_{D0} - \frac{2}{v^4}\cdot\frac{2\cdot(m\cdot g)^2}{\rho^2\cdot S^2\cdot\pi\cdot AR\cdot\epsilon}$$
Now bring $c_{D0}$ to the other side and re-insert the lift coefficient. The result is:
$$c_{D0} = \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
This means that the optimum lift-to-drag ratio is reached when the zero-lift drag equals induced drag. Total drag is the sum of both and in this case equal to twice the induced drag. Written in coefficients, this is:
$$c_D = \frac{2\cdot c_L^2}{\pi\cdot AR\cdot\epsilon}$$
Written as the lift-to-drag ratio, this becomes:
$$\left(\frac{L}{D}\right)_{opt} = \frac{\pi\cdot AR\cdot\epsilon}{2\cdot c_L}$$
Since the optimum lift coefficient can be expressed as
$$c_{L_{opt}} = \sqrt{c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$$
this can be inserted and the lift-to-drag ratio can be written as
$$\left(\frac{L}{D}\right)_{opt} = 0.5\cdot\sqrt{\frac{\pi\cdot AR\cdot\epsilon}{c_{D0}}}$$
The wing's aspect ratio is $AR = \frac{b^2}{S}$, and the mysterious drag surface must be $f = c_{D0}\cdot S$, and voilá, the strange equation is proven right. When the correct values are used, it is valid from mini paper airplanes up to Jumbo Jets and above. Airfoil drag is included in the zero-lift drag coefficient.


What do the regulatory bodies say about landing in CAT IIIB? I typically read that CAT IIIB approaches must be flown by an autopilot to touchdown. Looking for a reference (regulatory bodies* in particular) to track the statement only leads to company SOPs.

In other words, with the runway in sight at or above the DH, is it written somewhere (excl. SOPs) that the pilot flying can/can't take manual control when the approach was started in CAT IIIB minima?

Full disclosure: I completely understand it's unwise and unsafe to even suggest hand flying an approach when that's the view:

RVR 200 m. (wikimedia.org)

* FAA, EASA, and ICAO, are acceptable (I couldn't find anything in ICAO Annex 6).

The ability to perform autoland approaches requires specific approvals.  In the US, it is outlined in AC 120-28D Criteria for Approval of Category III Weather Minima for Takeoff, Landing, and Rollout. BTW, CAT I and CAT II approaches are covered by AC 120-29 Criteria for Approval of Category I and Category II Weather Minima for Approach.

The AC describes the necessary installed equipment, specific crew training requirements, and the need for operational procedures.  Once approval is granted, the crew training and operational procedures become part of the airline Op Spec.

If any hand flying is allowed, it will be spelled out in the Op Spec. Since Op Specs do vary from airline to airline, it's not possible to state definitively what is or is not allowed.

That said, it is physically possible to manually take over and land the aircraft. If the crew has the runway in sight at 200 feet, it's really no different that a CAT I approach. At 50 feet on an autoland approach, the autopilot will be starting the flare and de-crab maneuver, so manual intervention at this point may or may not be allowable depending on the specific aircraft performance and the airline's operational philosophy.


Could a larger consumer drone "take down" a passenger plane? As a frequent flier, I'm just concerned about my own safety.

Could a larger consumer drone, such as DJI Inspire, (intentionally) "take down" a passenger plane?

When I say take down I mean causing the plane to crash or emergency land.

I guess just a contact would not do too much harm but could it do some when flying in the engine?

Considering that larger drones can easily carry bigger cameras, it could also carry a 1kg or similar of explosives.

Are drones the biggest threat to commercial airlines as anyone can buy them and the chance of finding the pilot is very small?

If your definition of drone is any remote control aircraft freely available to consumers, then the answer is yes, but highly unlikely.

Its very unlikely, but it is possible. First, I'd like to point out that Radio Controlled Aircraft (RC Aircraft) have been available to consumers since at least the late 1950s. Hobbists build RC aircraft all the time, and when I was a kid I built my own RC aircraft that was much bigger than most commercially available "drones". To focus on drones alone misses a big slice of the pie. RC aircraft are sometimes built as 1/4 scale models of the original aircraft and can weigh 100lbs or more, so imagine a remote control aircraft that is 25% the size of the real aircraft.

So, the potential has always been there for at least the last half a century for a remote control aircraft to have enough mass to potentially cause a serious collision with a real aircraft. Imagine if a couple of 18lbs geese took down  Flight 1549, what would a 100+lbs quarter scale RC Aircraft do.

Personally, I've never been too concerned with this because I've flown both RC aircraft and real aircraft. It would be extremely hard for a drone or RC aircraft pilot to target an aircraft and hit it in its most vulnerable locations such as cockpit or engines.

So, yes, its possible, but I would not lose any sleep over it.


Do ETOPS rated airplanes ALWAYS fly with ETOPS requirements? So, as this is kind of a confusing subject I want to make sure I get a real answer, that's why I ended up doing it here. As ETOPS rated airplanes need to fly with certain rules so they comply with all the requirments, I am having kind of a hard time understanding if ETOPS rated airplanes need to comply with , for example, fuel requirements in a short flight that doesn't actually need ETOPS procedures. Example:
An A330 ETOPS rated aircraft is making a short flight from KPDX to KSFO, does it have to carry the extra fuel for ETOPS requierments, departing and landing with the extra weight and reducing performance?

The short answer is No (as per the regulations)

The ETOPS regulations state that an aircraft conducting ETOPS operations must be compliant to ETOPS regulations regarding its configuration (based on engine count). But aircraft capable of operating ETOPS flights only need to comply with the Advisory Circular when actually flying ETOPS. In other words the ETOPS AC only applies when the planed route falls under the guidance of the AC.

  All two-engine airplanes and three- and four-engine passenger-carrying
  airplanes operated under part 121 are required to comply with §
  121.161. This regulation imposes special requirements for ETOPS for these airplanes. These operations are defined as:

  (1) Two-Engine Airplanes. These are flights whose planned routing
  contains a point farther than 60 minutes flying time from an adequate
  airport at an approved one-engine inoperative cruise speed under
  standard conditions in still air.

  (2) Passenger-Carrying Airplanes with More Than Two Engines. These are
  flights whose planned routing contains a point farther than 180
  minutes flying time from an adequate airport at an approved one-engine
  inoperative cruise speed under standard conditions in still air.

However, how an airline choses to route and use its fleet is up to them. Since ETOPS airframes may require different maintenance or other related things it may not be effective for a given airline to use ETOPS maintained aircraft on Non-ETOPS routes.


Does the FAA require a rating for night VFR? Does a PPL require a specific rating or endorsement for night VFR in the US? Night flying seems like a special challenge and I'd think the FAA would want you to show that you've had proper training for it. This question talks about currency requirements, but I can't find anything on a night VFR endorsement.

There's no separate night rating or endorsement in the US, it's included in the private pilot flight proficiency requirements (14 CFR 61.107) and the specific required experience is in 14 CFR 61.109:

  (2) Except as provided in §61.110 of this part, 3 hours of night
  flight training in a single-engine airplane that includes—

  (i) One cross-country flight of over 100 nautical miles total
  distance; and

  (ii) 10 takeoffs and 10 landings to a full stop (with each landing
  involving a flight in the traffic pattern) at an airport.

Some very minimal instrument training is also required, which can be helpful at night:

  (3) 3 hours of flight training in a single-engine airplane on the
  control and maneuvering of an airplane solely by reference to
  instruments, including straight and level flight, constant airspeed
  climbs and descents, turns to a heading, recovery from unusual flight
  attitudes, radio communications, and the use of navigation
  systems/facilities and radar services appropriate to instrument
  flight;

That all applies to private pilots; sport pilots may not fly at night. And as David pointed out, there is an exception to the night requirements under 61.110 for pilots in Alaska: they can skip the night training but if they do, they can't fly at night.


What happens if an aircraft is only stable at higher angles of attack? Does anybody know what will happen to an aircraft, if it is stable (in longitude) for let's say: -8° > angle of attack > 8° ?
So for angle of attack 4° the aircraft is not stable (centre of pressure is in front of centre of gravity), so the angle of attack will further increase until 8° where it becomes stable (centre of pressure behind centre of gravity).
So except that my aircraft will oscillate a bit, it should always return to a stable position, right?

I find it hard to come up with an actual example that behaves like postulated. Normally, airplanes are most stable at low angles of attack and lose this stability at higher angles.
But there is indeed one case where angle of attack stabilizes the airplane: A swept flying wing without a vertical tail. Like the Horten designs. Those would enjoy increasing directional stability with increasing angle of attack. Your limits are a bit extreme, but a Horten IV was directionally indifferent at high speed when the typical angle of attack of the root airfoil would be between 2° and 0°. At lower speeds the induced drag would help to pull the airplane out of a sideslip as explained here.
Due to the high inertial moment around the vertical axis this behavior can be controlled by the pilot because sideslip angles will build up slowly. But it is not pleasant since it needs constant control inputs and puts an unnecessary workload on the pilot which might interfere with other tasks like navigation and collision avoidance.
Of course, this example is not quite what you wanted, since a higher sideslip will not stabilize the airplane. Only pulling up will.
If we hypothesize that an airplane behaves as you postulated, it will tend to leave the unstable region, but this might happen both in positive or negative AoA direction. An excursion into negative angles of attack is rather unpleasant (have you ever flown an outside loop?) and will probably make the pilot pull up hard. What happens next? The airplane flies through the unstable AoA region and picks up more pitch speed, only to arrive in the stable region with such a force that it overshoots the AoA limit and either stalls or, given enough flight speed, breaks up.
The Saab JAS-39 Grippen had such an unexpected overshoot at the most unfortunate of times, namely during a flight display on the occasion of the yearly Wattenfestival in Stockholm in 1993.
Any instability in the regular operating region is a bad idea and an invitation for mishaps that could be easily avoided.


Are there any plans, designs, or prototypes for an electric ground effect vehicle? I have been searching around for any plans, designs, or prototypes for a small GEV. All I have found is a ground effect gas powered like this link:

or an all electric prototype for short distance travel (not ground effect) at this link (eviation alice):

Are there any ongoing plans to build an electric-powered ground effect vehicle?
Would it be any better or faster than the current water taxi or ferry services?

The primary limiter is this: with batteries of current design, an electric GEV that can lift itself and travel a useful distance consists mostly of battery mass, with little useful payload. This is because a pound of jet fuel packs a lot more punch than a pound of battery.


Is the elevator really an 'angle of attack control' as described in Stick and Rudder? I've been reading Wolfgang Langewiesche's book Stick and Rudder and am a little confused about the definition of the elevator as the "Angle of Attack Control" or rather, the idea that each position of the elevator corresponds to a unique angle of attack.
I was under the impression that Angle of Attack is the angle the wing meets the relative wind. Consider a certain elevator position for straight and level flight at cruise rpm. If I then add power and climb (while holding the same attitude) isn't it true the Angle of Attack will increase because the relative wind is now coming from in front and above the plane? If this is true, then how can I reconcile this with the idea the elevator is an "angle of attack" control. Isn't the plane's Angle of Attack based on not just the position of the elevator, but the motion of the plane through the air?
If anyone could give me some advice to clear this up it would be greatly appreciated!

Wolfgang Langewiesche is right to appropriate order of approximation. For every elevator position a statically stable airplane settles to a specific equilibrium angle of attack. That's how static stability works.
Airplane is statically stable if and only if increasing angle of attack causes higher increase in coefficient of lift on the aft airfoil (tail for normal layout). Then increasing angle of attack (by random fluctuation like turbulence) increases the lift aft more, the overall centre of pressure moves aft and the aircraft pitches nose down to return the angle of attack to the trimmed position.
By moving the elevator you adjust the coefficient of lift on the control surface, and the plane needs to assume a different angle of attack to shift the centre of pressure back to coincide with centre of gravity. Most aircraft are designed so this is quick enough that if you don't jerk the controls too much the angle of attack simply follows the elevator position.

isn't it true the Angle of Attack will increase because the relative wind is now coming from in front and above the plane?

The angle of attack is high when the relative wind is from below and low when it is from above.

If I then add power and climb (while holding the same attitude)

If you add power and leave the yoke as trimmed, the plane will start to accelerate, which increases the lift. That causes the plane to accelerate upward, which decreases the angle of attack. This decreases the lift more on the tail, so the tail sinks and the aircraft pitches up until it assumes the original angle of attack. At this point, the pitch angle is increased by the same amount as the flight path angle.
The aircraft is still moving faster than the original speed due to inertia, so the lift is still more than weight and the aircraft continues accelerating up and pitching up to maintain the angle of attack. When the speed returns to the trimmed, the aircraft is already pitched too much, so now it will slow down and pitch down again and repeat the cycle. This is called the Phugoid oscillation. In most planes it is damped, but still annoying if you don't counter it with a bit of elevator deflection. But if you don't touch the trim, just arrest the phugoid, the aircraft will settle in climb at the same speed.
It has some consequences:

Tendency of the plane to pitch down means it is losing airspeed.
If you are not pulling on the yoke, or trim aggressively nose up, you won't stall. Unfortunately pulling on the yoke to keep the nose up becomes too much of a muscle memory so it's easy to miss this clue.
It is how pitch for speed and power for descent rate works on descent.

See also How It Flies, specifically section 2.3 talks about trim and angle of attack, with more details further in chapter 6.


Why not use the engine of a model aircraft for other purpose? I was reading the DLE-120 engine User Manual and saw this sentence:

This engine was designed for use in a model aircraft. Do not attempt to use it for any other purpose.

Why? Why not use the engine of a model aircraft for other purpose? What does mean "model aircraft"? Does this mean only RC aircraft or RC and UAVs?
Is there any technical or safety reasons why this engine could not be used in a different application, not involving a model aircraft?

A lawyer wrote that. It means if you use it for any other purpose, they are not liable and you are.


Does "resume own navigation" also mean "altitude your discretion"? In VFR flights from class C, I sometimes get resume own navigation, altitude your discretion after departure and sometimes just resume own navigation.

Does resume own navigation alone mean altitude your direction as well?

Update:

Let's assume scenario below for KSNA and to be more specific:

Pilot to Clearance Delivery: 529J with request

Clearance Delivery: 529J go ahead

Pilot to Clearance Delivery: 529J is Cessna 172/u west side parking, requesting
El Toro departure to Chino with information Bravo

Clearance Delivery to Pilot: After Departure turn left heading 080, Maintain VFR at or below 2400, SoCal on 124.1, SQUAWK 0210

Pilot: reads back …

Pilot starts taxi then take off with proper radio communication with ground and tower. After departure Tower hands pilot over to SoCal.

Pilot to SoCal (initial call): SoCal 529J departed John Wayne, 1100 climbing, requesting 3000 to Chino

SoCal to pilot:  529J resume own navigation

Here is the confusion, sometime SoCal comes back with only resume own navigation. Does this mean pilot can climb to 3000 or altitude restriction for 2400 still valid?

At this time, the definition of "resume own navigation" is very varied from group to group. ATC Controllers say that if there is an altitude restriction, they have to clear it. So safest thing to do is to ask for clarification if you had an altitude restriction/not told "altitude your discretion" that would continue into the "resume own navigation" exactly what you are doing now.

Source


Where should I sit to experience the least turbulence? Following on from Why are first/business class seats at the front?, in which part of a large commercial jet cabin would I experience the least turbulence? On the one hand I would have said that sitting near the wings (near the centre of gravity) is best, but subjectively it feels like the ride near the front is "smoother". Can anyone give me some more solid information? I imagine it also depends on the aircraft type?

The elasticity of the fuselage does indeed dampen the load factors from gusts somewhat. Therefore, gust-induced accelerations are a little higher over the wing than in the forward or rear fuselage. If the gust causes a pitching motion, this creates its own accelerations which adds to the bumps from the vertical accelerations. Elevator deflections cause similar pitching motions, and their accelerations are more pronounced in the rear fuselage since the aircraft will pivot around a point ahead of the center of gravity.

The main factor, however, is the location of the axis of rotation of the Dutch roll eigenmotion of airliners. This is a weakly damped oscillation which creates lateral accelerations which are bigger the more aft you sit in the fuselage. The Convair 880 was hurriedly test-flown with nobody sitting in the back, and the pilots were happy with its comfort level. The first passengers, however, got seasick from the Dutch roll motion, which was only detected when the passengers sitting in the rear of the cabin complained.

Modern airliners offer better comfort thanks to artificially enhanced stability, but even there you are better off sitting in front. I once flew on an Egypt Air Boeing 777 from Cairo to Frankfurt, and the captain flew through the tops of Cumulus clouds sitting over the Alps. Soon the obvious sounds and smell told me that people in the back were filling their air sickness bags. Maybe half of the rear third of the seats was affected, while the forward two thirds had only a few cases of airsick passengers.


Can gliders and single-engine planes have vortices? I read,

A third physical explanation of the source of induced drag is that the
wing tip vortices contain a certain amount of rotational kinetic energy. This
energy has to come from somewhere; indeed, it is supplied by the aircraft
propulsion system, where extra power has to be added to overcome the
extra increment in drag due to induced drag.

[Source: Introduction to Flight by John D Anderson, Sec: 5.3 "Finite Wings"]
And interpreted thus,

Vortices have rotational energy which comes from propulsion. This additional requirement of "Thrust" can be balanced with Induced drag.

And this makes me question, how gliders form vortices when it does not have engines? Or even single mounted engines in prop planes that do not have engines on wings?
Could you see the vortices created by the glide of owl in the video here and here?
Also, if the phenomena of vortex is not due to engines than why there are four vortices in this famous image:

The vortices that you are referring to (I think) are wing-tip vortices, a product of the wing generating lift.  Since glider wings do generate lift (due to the airflow over the wing) and are propelled (without engine created propulsion) wing-tip vortices are created. Single engine airplanes also create wing-tip vortices since lift is being generated (aided by propulsion)
The jet in your photo is showing "vapor trails" or "contrails" from condensation (from the engines' exhaust) and are not wing-tip vortices.
I'm pretty certain there are a number of engineers on ASE that could provide a more technical answer, but the bottom line is the engines of an airplane do not create vortices (in the context of wing-tip vortices that I believe you are thinking of).


What are the aerodrome services SRE and CEV? eAIP in France list two services on AD-2 (aerodromes) for which I have no clue what they stand for. They are not known to AIXM neither.

SRE found on eAIP of aerodrome LFOA
CEV found on eAIP of aerodrome LFBD

Any idea what these services are? Thanks a bunch!

When in doubt, check GEN 2.2 for a list of abbreviations.

  CEV
  Centre d’essai en vol
  Flight test centre
  SRE
  Elément radar de surveillance du système radar d’approche de précision
  Surveillance radar element of precision approach radar system


What information an aircraft responder must give to mode S ground receiver What is the minimum set of information (for ex.: aircraft registration, position, altitude ... and what else) that a transponder in an aircraft must provide after being interrogated by a ground station ? Is this defined somewhere ? Is there information about the airport of departure/arrival ?

From Mode-S.org

An ADS-B message is 112 bits long:

+--------+--------+-----------+--------------------------+---------+
|  DF 5  |  ** 3  |  ICAO 24  |          DATA 56         |  PI 24  |
+--------+--------+-----------+--------------------------+---------+

DF is the downlink format, ICAO is the 24-bit ICAO identifier of the aircraft, DATA is the message being transmitted, and PI is the parity/interrogator ID.

There are a number of different message types available:

The messages transmit things like position, altitude, turns, track, airspeed, roll angle, turn rate, etc. But they do not contain any information about the originating airport or the destination.


Can pilots hear their passengers clapping on touchdown? Something that just popped into my head: I've been on a few easyJet and Ryanair flights where a lot of passengers clap and cheer on touchdown. Would the pilots be able to hear this?

Here's an example I found by searching YouTube:

It seems pretty commonplace... but can the pilots hear them? I guess it would be distracting.

Just something I was wondering!

In my 10 years of flying 747s on international flights, there was no way we would know of passenger reactions upon landing unless one of the cabin staff told us, and that was rare.


Does the large 6-pointed star on a sectional warn of dangerous radar facility? I cannot find an explanation for this symbol on the chart legend.

Example: near BAB, Beale AFB, on the San Francisco Sectional Chart, does it warn of the dangerous radar facility?

Source: skyvector.com

There are two stars:

The large multi-pointed Star (6 pointed in this case) is described in the Aeronautical Chart User’s Guide as an indicator of High Energy Radiation Areas. The Precision Acquisition Vehicle Entry Phased Array Warning System (radar) may be intense enough to damage avionics. Or, at least cause them to give false readings.
The blue star with the clear circle in its center indicates that the airfield has a rotating light beacon and the beacon’s location relative to the field. The beacon’s location can be used to differentiate one airfield from another while in flight at night.

Reference: Aeronautical Chart User’s Guide


Are ADS-B Airborne Squitters inherently inaccurate? Right now I am reading related passages/sections from ICAO Annex 10 Volume 4 and Technical provisions for Mode S Extended squitter.
Airborne position squitters are randomly distributed in between 0.4 and 0.6 seconds. Even if we update Airborne Position Register 05 with utc-synced estimated position, transponder's choice of transmit time might cause in shifting into next epoch(basicly 0.2 second lag).
Increasing rate of update(5hz suggested for now) might only reduce the problem.

Are ADS-B Airborne position squitters inherently inaccurate?

Yes, there is a inherently inaccuracy caused by the delay between a position is determined by the GPS receiver and the time it is transmitted.

However, for installation certified for the EU and USA ADS-B regulations, the inaccuracy is very limited. The accuracy of ADS-B is therefor better than radar even when ignoring the latency in radar systems.

The first part of the latency is caused in the GPS unit itself; there is some processing time between the position signals arrive at the GPS antenna and the  of the time of output of the computed position. Further delay can occur if the GPS-receiver is not directly wired to the transponder. If the position signal has to travel through another box (for example the ADIRU) additional latency can occur.

Finally the position arrives in the transponder and is delayed until the next position message is scheduled for transmission.

In installations certified for the ADS-B mandates of the EU and the USA, the position latency is limited to 0.6 seconds. This is usually achieved by direct wiring the GPS to the transponder. Additionally the latency is compensated for by extrapolating the position using the ground speed vector. The position within the transponder is thus update periodically (e.g. at 10 Hz) using the groundspeed vector. This extrapolation reduces the effect of latency by introducing a small error based on the accuracy of the groundspeed vector and any manoeuvring going on.

The total accuracy of the ADS-B signal is the combination of

GPS accuracy
accuracy of speed vector used in the latency compensation
manoeuvring going on between the time of position validity and time of transmission not compensated for by the linear extrapolation using the speed vector
residual uncompensated latency

In some installations the residual uncompensated latency is negative (i.e. the position is over-extrapolated). The limit is 0.2 seconds ahead of the current position. The recommendation in the ADS-B Minimum Operational Performance Standard (MOPS) is that the uncompensated latency should not be more than 0.4 seconds.

Note that most of the inaccuracy due to latency is only observable in the along-track direction.

The magnitude of the position error caused by the latency is very limited.
For an aircraft flying 270 meter per second (972 km/h, 525 KTAS), the upper bound of 0.6 seconds latency limits the error to 162 meter. That is much better than the position accuracy that en-route radars typically achieve (and in addition, radar also has latency).

In the TMA, the speeds are usually slower and so are the latency induced errors. So ADS-B here outperforms the TMA radars.

For reference, the 0.6 seconds is a limitation in the USA is from FAA AC20-165A (PDF) and in the EU from EU 1207/2011 (applicability dates amended by EU 1028/2014). The full Certification Specifications for ADS-B in the European Union can be found in the CS-ACNS.


What is this turbine engine panel that opens on landing? Tonight I flew from Munich to Dortmund on an A319 and I happened to sit just above the wings and turbine on the right side. Upon landing, the turbine opened a window or panel which exposed some grid like structure inside it and just a few seconds later, after touchdown, closed it again. Could someone explain to me what that is, how it is called and what its purpose is?

What you saw is the thrust reverser of the engine, which redirects some of the airflow forwards and therefore helps slowing the aircraft down. The grid like structure are the cascade vanes. This is what it looks like inside the engine:

(Airbus A380 FCOM - Engines - Thrust Reverser System)
The blue arrows indicate the flow of the so called bypass air, which is air that goes through the fan (and is therefore accelerated), but does not go into the core engine. With the thrust reverser deployed, this air is redirected forwards. The core air going through the actual turbine engine will still exit at the back.
Since there is more bypass air than core air1, there is a net thrust generated in the forwards direction.
If you are wondering what the pilots are doing to engage reverse thrust, this is a picture of the A320 family thrust levers:

(image source)
The main thrust levers are pulled all the way back during the flare to the position shown in the image (labelled 0). To open the reverser doors, you pull up on the smaller handles at the front of the thrust levers. Once the reverser doors have opened, the thrust levers can be pulled backwards to add more reverse thrust (range labelled REV in image). To close the reverser doors, the thrust levers are moved back forwards and the smaller handles are pushed back down.
Note that on a dry runway reverse thrust does not slow the aircraft down faster (assuming auto brakes are used). The brakes on the main landing gear are capable of achieving the same deceleration without reverse thrust. Engaging reverse thrust therefore reduces brake temperatures and wear.
The thrust reverser doors can look different depending on the engine type. Based on your image, the aircraft you were on was equipped with IAE V2500 engines2. The reverser doors on the CFM56 engine, as used on some A320 family aircraft, look a bit different3:

(image source: Wikimedia)

1 The IAE V2522-A5 engines used on the Airbus A319 have a bypass ratio of 4.9 : 1 (source).
2 FlightAware shows a EWG4063 flight tonight from Munich to Dortmund and according to planespotters.net Eurowings uses IAE engines on their A319s.
3 The CFM56 engine is also used on the 737, but uses the cascade thrust reversers there (thanks to DeepSpace for pointing this out). See also Why is the CFM56 produced with two different thrust reverse options?


Using ANR aviation headset with a PC I just started my studies towards PPL, and am looking into buying a good ANR aviation headset for flying on Cessna 172.

I have an office job, and I'm dealing with a lot of noise, hence ideally I'd like to use this headset with my computer as well (as buying 2 ANR headsets for different purposes is quite an expense).

From what I understand aviation headsets normally have 2 jacks with a different diameter. There are probably adapters to convert them to a standard 3.5 mm jack, but I wonder if it affects its noise reduction capabilities.

Conversely, can I buy a PC-compatible headset, and use it for flying with an appropriate adapter?

Also, most ANR headsets seem to operate on AA batteries. Are there any with lithium-ion battery instead, so that it can be recharged?

The answer to all of our questions is broadly yes, but to break it down:

This company makes mic's for the Bose ANR audio headsets (quiet comfort line) that may fit your use case.

You should be able to use a step up adapter to plug any standard aviation headset into 3.5 mm. It might be worth noting that many of the headsets out there now have bluetooth that you can bus audio through including the mic audio for talking on the phone. However its worth mentioning that most aviation ANR headsets are bulkier than your typical ANR headphone as they also offer passive isolation should the batteries die.

AA batteries are the chosen option as they can be easily sourced just about anywhere and quickly replaced. Some people may chose to use rechargeable ones. I would think the lack of battery options has more to do with the fact that for a situation beyond regular old batteries many people may opt for the panel power variants.

FWIW the audio quality (for music) is decent but not headphone quality on my zulu 3 as most aviation headsets are designed to work well in the voice range and not necessarily the full frequency spectrum range that a set of headphones will work well in.


Why is the tail group of virtually every airplane swept instead of straight? Even low performance airplanes like ultralights have their tail group (vertical and horizontal stabilizer with rudder and elevator) swept backwards knowing fully well that a straight tail group will produce more force than a swept tail group of the same area. Is the sweeping of an airplane's tail group simply aesthetics or is there some aerodynamic advantage involved?

The reason why I'm asking is because I'm trying to design and build an ultralight and was wondering if I can just build a straight rectangular tail group as seen below (for the sake of simplicity).

There is more to it than just looks.

One immediate benefit is a more backward location of the center of pressure on the backwards swept surface. But that effect is small and has to be bought with a lower lift curve slope, i.e. lower effectivity at low angles of attack rsp. sideslip.

But once sweep is big enough, it will extend the useable range of sideslip angles at which the tail is effective. Sweep reduces the lift curve slope but extends its linear range to higher angles, so the maximum lift per area of a swept surface is about as high as that of an unswept surface. This is especially true for low aspect ratio wings where the outward movement of the boundary layer is not a big factor. Therefore, the aerodynamics of a vertical tail suffer much less from the usual sweep effects we know from swept wings.

Adding a fillet ahead of the root of the vertical tail increases this effect further and has been instrumental in making designs like the Boeing 307 spin proof. Before that change the Boeing 307 prototype suffered separated flow on the vertical in a spin and crashed when the aircraft oversped in an attempt by the pilot to end the spin by applying differential thrust.

While the wing operates in a narrow range of angle of attacks and straightens the airflow for the tail, so the horizontal tail is able to work within an even narrower range, the fuselage creates an unstable yawing moment over a much larger range of angles of sideslip. In order to have enough directional stability even at high angles of sideslip, a swept vertical tail is very helpful. Yes, this swept tail needs to be larger than an equivalent vertical tail which is designed for single-digit angles of sideslip, but this straight tail will render the aircraft unstable once it ventures into higher sideslip angles.

Reference: NLR Report A-1582. Sorry, I found no online source. It is discussed in Ed Obert's "Aerodynamic design of Transport Aircraft" on page 418.

Horizontal tails do not need the extended working range - here, it is enough to add stabilizer trim in order to adjust tail lift for different wing flap settings. Besides, building a horizontal tail with a swept hinge line is much more complicated than building a straight hinge line, so most horizontal surfaces have just a little sweep such that taper and sweep together result in a straight hinge line.

But there is one exception: In the early 70s many glider designs used a full-flying, swept horizontal tail, like this Standard Cirrus below (picture source):

This is obviously not for compressibility. By sweeping the tail its center of gravity can be moved close to its center of pressure, so this tail needs no mass balance and has low actuation forces. The downside is the rigid, symmetrical airfoil: At low speed and higher angle of attack it has very little effectivity because the flow stays separated while a conventional tail with a fixed stabilizer will already show attached flow. This led to a number of fatal crashes in winch launches when the aircraft would pitch up into a stall and could not be controlled.


Why wasn't there a belly gunner on the B-25 Mitchell? The B-25 Mitchell doesn't have a belly gunner, which would seem quite dangerous. Why didn't it have one?

The production B-25B, B-25C, B-25D, and some B-25G models did have retractable remote control belly turrets. They were often removed in the field because they were ineffective and disliked by the crews.

The lower turret was officially deleted in the middle of the B-25G production run and continued with the B-25H and B-25J production.

More info on the B-25 here: B-25 History.org


What is the working principle of gravel kits? In this answer gravel kits are mentioned. I then looked at the wikipedia page and I noticed that they are quite different from what I was expecting:

I was expecting some kind of "shield", plate or extended inlet on the bottom side of the engine.
Wikipedia says that these instead are

  vortex dissipators, using compressor bleed air

How do they work? How does a beam and a sidewise jet of air prevent FOD ingestion?

Notice the path of condensation leading up from below this engine into it:

That image was taken from this video, and it clearly demonstrates that there exists a path of air which flows from ground level up into the engine. Any debris on the ground is liable to be sucked up in that vortex. The nozzle is designed to break up the flowing air on that specific, well-known path.

Note that even when there is no condensation to make the vortex visible and obvious, it still might exist.

Here is a nice intake vortex video, and here you can see the vortex swirling on the ground. This video really shows off a C-17's huge vortex during landing.


Is flying without sunglasses in daylight doable in a Cessna 172? Do the windows in a 172 provide any protection from the sun or is too bright? Particularly, if one wants to do a flying lesson and was told to bring sunglasses more than once.  So, is it critical?  My friend doesn't have sunglasses and would have to get prescribed ones which he can't get now. He got a gift of a flying lesson so he wants to try it but is being in the plane without sunglasses doable?  Or will he be squinting the entire time? Or is it really bad for your eyes?

Definitely doable. No real protection from the sun just through the windshield but I flew a C172 for many years only using sunglasses occasionally. Just don't make the same mistake I did when I first started flying- paid a lot for a pair of polarised sunglasses then jumped in the cockpit and all the LCD screens went blank! :)


What does the extending the flaps do (or any high lift device) to the Rate-Of-Descent of an airplane? I know that deploying flaps will increase both drag and lift, thus increasing L/D ratio. But how exactly does that correlate with the increase/decrease of the rate-of-descent?

According to the FAA, lowering or extending flaps allows one to increase drag without an increase in speed.  This increases descent rate for a given speed.

One must be careful to consider what factors are held constant to evaluate the effect.  For example, one can lower flaps during level flight. This will result in a lower pitch attitude--since they produce more lift, less angle of attack is required.  If power/thrust is not increased, speed will decrease due to increased drag.

However, an aircraft flying at a constant speed will descend faster (higher rate of descent) if the flaps are extended compared to when they are not.


How "full-motion" is a full-motion simulator? How "full-motion" are simulators?  Do they just simulate the major motions of the airplane in response to the flight controls, or do they also simulate the minor forces of the flight, such as the vibration from the engines?

(Bonus question: if they simulate engine vibration, do they simulate the severe vibration from an engine that's just thrown a fan blade?)

Full Motion is full in the sense that it can generate cues in all 6 Degrees Of Freedom: fwd/aft, left/right, up/down, pitch, roll, yaw. The term came in use to distinguish between 6-DOF systems and the earlier 3-DOF systems which only produced pitch, roll, heave cues.

  Do they just simulate the major motions of the airplane in response to the flight controls...

They simulate the aircraft response by stimulating the sensations felt by the inner ear, making use of its limitations as also mentioned in this answer.

The two side-questions about reproduced vibrations boil down to the frequency response of the motion system: the ability of the system to reproduce commanded vibration signals, as measured at the upper platform with the payload installed. Older hydraulic systems, such as depicted above, had a very limited frequency response - the servo valve opens and oil flows through, creating dynamic flow effects and springiness from the compressibility of the column of oil supporting the payload. Yes, oil is compressible. Maximum perceptible cues up to 5 Hz.

Electric systems have an electric motor at the bottom of the actuator. Electric field creation happens almost instantaneously when commanded and the connection to the upper platform is through the metal screwjacks inside the tubes: frequency response is almost an order of magnitude better than that of hydraulic systems. Maximum perceptible cues up to 30 Hz. Enough for engine vibration reproduction, severity depends on the magnitude of the amplitude.

The issues with reproducing severe vibrations at the motion upper platform are:

The cabin construction must be able to rigidly stay in one place and support the visual projectors without starting to wobble the image that the pilots are looking at - the rigidity of the upper construction must exceed the frequency response of the motion system. We've seen simulator cabins bobbing about like a gelatine pudding when subjected to serious amplitude/frequency combinations.
All instruments, electronics, cabling etc. are subjected to the alarming vibrations as well.

Both issues above are not an issue if the constructional design of the cabin etc. has incorporated the vibration inputs. The alarming vibrations are extremely effective training cues, and can be faithfully reproduced by an electric motion system plus suitable cabin construction.

Another way of producing severe high frequency vibrations are by means of a seat shaker or cabin shaker, used in the olden days of hydraulic motion, particularly with helicopter simulators for reproducing the main rotor vibrations. The seats would be mounted on up/down platforms with a stroke of several centimetres, actuated by a separate hydraulic small actuator.


What are the consequences of fouled spark plugs in flight, and how can I clean them? I've experienced spark plug fouling before but it was during the pre-flight checks and my instructor fixed it for me (by using max RPM and leaning the mixture a couple of times). But now that I have to fly all by myself, I'd rather know what to do and what not to do, especially during flight. What happens if the plugs become fouled in the air, and how do I clean them in flight?

You should read up here but generally speaking plugs are less likely to foul in flight (and is why its not talked about much). Plugs often foul due to the mix of low engine temps and high led content during warm up at full rich settings. This is why a leaned out warm up is advised for some planes, you should talk with your instructor about the plane you are flying and what the proper warm up procedures are.

Please consult your POH for any airframe specific emergency checklists that may apply to your aircraft. Generally speaking if you depart with a fouled plug and it is causing a rough running issue you should cycle the magnetos untill you are running on the good set of plugs and get the plane down safely. This is most likely the result of a poor or non-existant run up check. Unless you are sitting in line for a long time after your runup, you should generally be doing runup close to departure time.


What are the mass flow rate and exhaust velocity for a CF6 or GE90 turbofan? For a typical turbofan jet engine (two examples given in the title), what is the exhaust velocity and mass flow rate of air at sea level and cruising altitude (~ FL350)?

Also, does the specific impulse vary at different altitudes, since the density of air decreases with increases in altitude?

According to The GE90 - An Introduction, the GE90 has a mass flow rate of 1,350 kg/s at take-off and 576 kg/s at cruise (at 10.668 km = FL350). The CF6 has a mass flow rate of 591 kg/s at take-off.

Exhaust velocity isn't generally quoted, perhaps because it only bears a loose relation to the performance characteristics of the engine. I suppose if you wanted you could find the area of the exhaust and use the density of air to find the velocity.

Looking specifically at the GE90, we see that it has take-off SFC (specific fuel consumption) of 7.9 mg/N-s. Using the formula $I_{sp} = 1/(g_o·\text{SFC})$ given in paragraph 4 of the Wikipedia article Specific Impulse we get a specific impulse of 12,285 s. If we use the cruise SFC of 15.6 mg/N-s, we get a specific impulse of 6,536 s. Is this an effect of the lower density of air, or simply of the lower fuel required in the cruise? I don't know.


How to fly a drone in Class D in Italy? I am traveling for a wedding which will take place in Monza Park, Italy. According to Italian Airspace Pro, the location I would like to fly, the southern half of the park, is technically in Class D airspace, which is restricted unless cleared by ATC.

Click image for full view.

I know that in the United States, the FAA regulations state that to fly in restricted airspace, you must:

  Notify the airport and air traffic control tower prior to flying within 5 miles of an airport*

Is flying within restricted airspace possible if I contact a local tower there? Who would I need to contact?

The class D airspace you are referring to is a control zone (CTR). According to article 24 of Regulation for Remotely Piloted Aerial Vehicles, the following applies to VLOS operations (emphasis mine):

Except as required by point 6 below, RPAS operations shall not be conducted:

a) within ATZ and beneath take-off and landing paths or at a distance less than 5 km from the airport (ARP or published geographical coordinates) where ATZ is not established;
b) within CTR, without prejudice to point 5 below;
c) within active restricted areas and prohibited areas.

Operations within CTR are permitted only to RPA with operating take-off mass less than 25 kg, up to maximum height of 70 m AGL and within maximum horizontal distance of 200 m. Beneath take  off  and  landing paths, beyond ATZ boundaries and up to 15 km from  the airport, maximum height shall be 30 m AGL.

When  operations  do  not  meet  the  requirements set  forth  in  points  4a), 4b) and  5 above, operations shall be  carried  out  according  to  procedures  published  by  ENAC. When it  is required to operate within airspace as referred in point  4c) above,  operations  shall  be subject to specific authorization according to procedures published by ENAC.

Although you are pretty much directly below the approach path to Linate's runway 18, since the park is just over 15 km from the airport, you should be OK to fly up to 70 metres above ground as long as the drone stays within 200 metres of you.
Of course, there are also other applicable rules to consider: for example, you must wear a high vis vest with "Pilota di RPA" printed on it, you are not allowed to overfly crowds (including wedding guests) and the drone must be registered and identifiable.


Is there any way to tell the difference between MD-80 models? When I was at the airport a month ago I spotted a McDonnell MD-80 and took a picture of it and was very interested in this historic aircraft. I looked up the specs and this is what turned up. The MD-81,82,83, and 88 models all have the same fuselage length(147ft 8in) except for the 87 model(130ft 4in). They all have the same wingspan at 107ft 8in and the 81,82,83,88 carry 172 on a one class cabin except for the 87 which carries 139 on a one class cabin. So is there any way to tell the difference between the 81,82,83, and 88 models? The picture I took of the MD-80?

For Delta, it's either an MD-88, or an MD-82 reconfigured as an MD-88. The differences between the 81/82/83/88 are engine, fuel, and flight deck options. MD-87 is visually shorter than the others.


What should I do to become a commercial pilot? I am 25 years old, I have completed my bachelor  degree  from electrical  engineering. So what should I do to become a pilot?

If you plan to train and fly in the US...

You should spend that money on an MSE or MBA, get your private/instrument, and then buy your own plane and fly whenever you want.

However, if you feel you must become a commercial pilot you should find a local flight school and lay out a plan with someone who has authourity to negotiate pricing.

-lay out your objective.  You are paying for a private license, instrument, all of the time building for commercial, and then commercial.  That's a minimum of 250 flight hours plus a lot of billable hours for a very lucky CFI.  You can negotiate an awesome rate if you guarantee the school that business in s short amount of time.

-DO NOT pre-pay more than $1000 at a time.  Keeping funds on account is fine, just don't give them more than you're comfortable losing if suddenly they close.  It happens.

-stick to a schedule.  Fly a lot.  It's cheaper to knock it all out at once.  You have to relearn stuff if you only fly once or twice a week.

-don't get caught up comparing part 61 and part 141 schools.  Just go with the most affordable option.

-research airline minimums.  A commercial cert won't necessarily get you a job.  If fact, a commercial cert means very little wothout hours to go with it.  Think about adding a CFI cert to your shopping list.


Why do budget airlines not use the jetbridge that's right there? Related to Who decides whether an airline docks at a jetbridge or parks at a remote stand?, but I'm not asking about remote stands.

I recently took an easyJet flight (A319/320) from London Gatwick (LGW) to Malaga (AGP), and once through the gate, we walked down some stairs adjacent to the jetbridge and out to the plane. We didn't use a bus.

But the airbridge was right there. Why not use it?

The answer to the question you link explain many of the reasons. But aside from them, all valid, the main point is that the use of jet bridges is charged an extra fee from the airport. Some airport charges for use, some charges for time, so a low cost company which is trying to save money is going to save on the jetbridge too.


How to calculate altitude in a flight simulation? I guess altitude from sea level in the real aircraft is read from barometer, while for the altitude from ground a radar is used. For the purposes of very simple simulation, and assuming aircraft is on ground at certain airport at certain altitude.

The starting variables are then nothing but a throttle position, which over time increases, which translates into speed. And once the aircraft is airborne also the pitch. For this purpose I would not assume any roll, wind or other factors. The aircraft engine has certain torque % and pilot pulls the nose up to achieve certain pitch.

Is it possible to get the altitude simply as the function of pitch and torque % Or to put it differently what are the minimum variables to take into account to come up with an altitude?

UPDATE

Obviously there's something wrong with the question because it resulted in the explosion of complexity, even touching the topic of atmospheric re-entry.

What I want to know is, as a pilot of a simple simulator, standing still on the runway, I can only change two things.

Throttle, and some time later
Pitch

I don't have to do anything else whatsoever in simple sims, I click on + to set the throttle to X, and when the speed is Y, I pull the nose up, and now the altitude keeps on picking up. How do those two changes to those two variables (throttle, pitch) eventually give me the altitude and speed, through a series of equations (that needn't be neither simple nor linear)?

You can't directly calculate the altitude of an aircraft from any set of control settings. The altitude is dependent on the history of the aircraft. For example:

Fly level at full power for one minute, and pitch up suddenly. You will be near the ground, having quite some speed.
Climb at full power for a minute. You will be at high altitude, going quite slow.

In both situations, your aircraft is pitched up and at full power, but at very different altitudes. So, what are then the minimum variables needed?

This answer is quite difficult to give. If you're making a professional simulator, thousands. If you're making a platform game, just pitch and power, as well as some way of knowing the history of the aircraft. Usually, this is just a stepped simulation: at each moment in time, determine what your current pitch and power do to the attitude and altitude of the aircraft, and save it for the next time step. Of course, you need some model for relating these variables to actual accelerations of your airplane, and again, this model can be as complicated as you want or need it to be. See Koyovis' answer for more details on such a model.


How much fuel do the new A320-Winglets burn vs. the B737-800? Now that the new A320-Winglets have established themselves, I'm wondering if they have better fuel consumption than the B737-800?

I was told that Boeing used to be marginally better. Is that still the case?

Airbus says this about their new blended winglets (aka "Sharklets"), being fitted to new A320s, and retrofitted:

  Airbus’ next step is the large Sharklets™ wingtip devices, representing another element in the ongoing continuous improvement programme for its best-selling A320 Family. These devices improve aerodynamics, reducing fuel burn by up to 4 per cent – which amounts to annual savings of more than 900 tonnes of CO2 per aircraft.

Given that an A320's fuel burn rate is approximately 5.13 gallons per seat per hour, reducing this by 4% gives you 4.92 gallons/seat/hr.

Comparatively, a 737-800 burns about 4.88 gallons/seat/hr.

Source:

  A 737-800 burns 4.88 gallons of fuel per seat per hour, compared with the comparable A320's burn of 5.13 gallons per seat per hour, according to The Airline Monitor, an industry publication.

So they're near enough the same.


What is that wing device that looks like a mini-spoiler on the CJ3? The Cessna Citation CJ3 (model 525B) has that device circled below, what is it?

Source: airplane-pictures.net

I initially saw it as a mid-chord fixed spoiler-like device. As @programagor commented, it's parallel not perpendicular to the airflow.

I found a hint in a worldofaviation.com article; it's an "aileron fence":

... a small 'aileron fence' rises from the upper surface, just inboard of the ailerons.

Now knowing what to look for and the angles to consider, it's now much easier to spot (and to not spot—knowing that shallower head-on angles would not show it).

Source: wikimedia.org

Wikipedia's Aileron article says:

Aileron fences Some aileron designs, particularly when fitted on swept wings, include fences like wing fences flush with their inboard plane, in order to suppress some of the spanwise component of the airflow running on the top of the wing, which tends to disrupt the laminar flow above the aileron, when deflected downwards.

But, it's citation needed
As seen below, when downward deflected, the aileron actually takes the fence down with it, so Wikipedia gets it wrong.

Source: wikimedia.org; this high-res photo shows it attached to the aileron

There's little literature on the device; I was able to find only one source where it's properly explained and makes sense:

In the presence of a sideslip from the wingtip direction of a given aileron, the fence creates a local high-pressure area on the upper surface of the aileron causing it to deflect downward and lifting the opposite aileron. This causes a stabilizing rolling moment away from the sideslip. Fences can also be installed on the lower surface at the outboard edge of the aileron and function in much the same way to create a low-pressure area to “suck” the aileron down. Although aesthetically preferable, these are usually less successful. Some examples of aileron fences used for static lateral stability can be found on a wide range of aircraft: Cessna 206 (single engine piston), Cessna 208 (single engine turboprop), and Cessna Citation CJ3 (twin engine turbojet, Figure A-7).
— Williams, Russell Loy. Reduced static lateral stability in airplanes. 2005. (PDF)

Another thing Wikipedia gets wrong as shown by that thesis, is that it's present on three Cessna models with straight wings.


How can I find examples of airports with specific approach types? Can you guys help me find airports with these approaches:

An airport with only an LNAV mins (so no LNAV/VNAV or anything other than just LNAV)
One with an LPV lower than 200 feet
One with an ASR approach. And what is an ASR approach?

An ASR approach is an Approach Surveillance Radar style approach. The guys on MZeroA.com flew one in this video at KLAN. They are not "at" any airport nor are there plates for them it is effectively a function of ATC. I have heard them flown at a few "smaller" class D facilities near me for practice. Generally to practice them you need to be somewhere that ATC does not mind clogging the radio up as they take a fair bit of radio work to fly.

The RNAV (GPS) RW1 into KWWD has only LNAV minimums. (Note: It also has circling minimums which most LNAV airports will have unless terrain or some other issue forbids a circling maneuver).

As far as I know there are no LPV approaches that take you lower than 200 feet as is regulated by the FAA:

  Localizer Performance with Vertical Guidance (LPV). An RNAV function
  requiring WAAS, using a final approach segment (FAS) data block, which
  computes, displays and provides both horizontal and approved vertical
  approach navigation to minimums as low as 200 foot ceiling and ½ mile
  visibility.


How much is alpha induced angle? I know that alpha induced rise with increasing AoA but how much is alpha induced in reality ,are we talking about 1-2 degrees or more?

The induced angle primarily depends upon the following:

Coefficient of lift
Aspect Ratio (AR)
The correction factor $\tau$ (needs to be accounted for if the wing platform is not an ellipse. If the wing platform is an ellipse, then $\tau=0$)

All three are related the with the following equation:
$$\alpha_i[\text{rad}]=\frac{C_z}{\pi AR}(1+\tau)$$

The table below provides the values of $\tau$ for a rectangular wing.

You can use these values and NACA Report 824 to calculate the actual induced angle of attack for a rectangular wing for any possible airfoil.

For instance, using $\text{NACA} ~65_1-412$ airfoil at $\alpha_{\text{geometric}}=8^{\circ}$ and $AR=9$ it follows that $\alpha_i=0.05~\text{rad}\approx 2.86^{\circ}$.

It varies greatly in relation to the angle of attack, as low as $1^{\circ}$ in high-speed flight with low angle of attack and as high as $3^{\circ}-4^{\circ}$ at low-speed flight for a rectangular wing aircraft.


How can I find the maximum climb angle of a propeller driven aircraft from a graph of vertical velocity against airspeed? I've been asked to find the maximum climb angle of a propeller driven aircraft from the graph of vertical velocity against airspeed:

How can I do that?

All you need to do is to plot vertical versus horizontal speed using the same scale on both axes. Then the solution is the point with the steepest angle from the origin of the graph.
Of course, it helps to do this in metric units. And to add a description to the axes of a plot. The solution can then be directly read from the graph.


Are there any GA trainer aircraft without toe brakes? I'm a student pilot, and I've built about 20 hours on a Cessna 172. I also have an old ankle injury that makes it hard to bend my left ankle, and I'll probably be getting an ankle fusion later this year. I know I won't be able to work the left brake with a fused ankle. Are there any good options for trainer aircraft with other kinds of brakes?

There are still many Ercoupes in the fleet that don't even have rudder pedals, never mind toe-brakes on the rudder pedals.
You may also want to consider arranging for a more commonly-available trainer (e.g. Cessna 152, Piper Tomahawk, Diamond DA20, etc.) to be equipped with hand-controls for braking. This is done for individuals who have any number of reasons that they can't operate the rudder pedals with their feet, such as paraplegia, deformity, etc.
See e.g. https://www.freedomintheair.org/hand-controls/, https://www.newmobility.com/2019/01/pilots-planes-hand-controls/, https://www.wired.com/2009/08/hand-control-airplanes/, https://abilitymagazine.com/hand-controls-for-flying/, etc.


Did Concorde's sonic booms affect other air traffic? Given that Concorde's sonic boom reached the ground, it also must have reached other nearby air traffic.

How was this dealt with? I imagine passengers would not welcome hearing a loud boom during their flight.

According to this airliners.net post (written when the Concorde was still flying, BTW), the Concorde's sonic booms could often be heard from other aircraft, but never posed problems for said other aircraft:

Sometimes, to the South of Ireland, during the early part of the acceleration on a Westbound flight, Concorde flies over subsonic traffic that is arriving from the USA and cruising around FL370-FL410. If close to this traffic, by which I mean 10-15 miles, then ATC will often warn them that they may be "boomed" as the shock waves pass over them.
From the reports I've heard from some of these crew, this can vary from nothing to a clearly audible double boom, but nothing to cause any concern or alarm.


What is vortex lift? In a recent question I asked, I was given an answer by Peter Kämpf and he described something about lift being created by a vortex used on delta wings and the Bird of Prey wing.

How exactly does vortex lift form to generate lift and on what other types of wing is it used on?

The vortex lift is the method by which highly swept wings (like delta wings) produce lift at high angles of attack.

In the case of wings having sharp, highly swept leading edges like delta wings, the leading-edge separation vortex phenomenon occurs at subsonic speeds. However, the separation does not destroy the lift as in the case of low sweep wings; instead, it forms two vortices which are (nearly) parallel to the wing edges.

Vortices over a delta wing with a sweep angle of 70°, Separation in three-dimensional steady flow, ONERA

In case of Concorde, the vortices look like this:

Vortices over the Concorde wing, Separation in three-dimensional steady flow, ONERA

A cross-section of the vortices looks like this:

Flow above the Concorde Wing, Separation in three-dimensional steady flow, ONERA

Unlike the (bound) vortex of the conventional wing, these are real in the sense that they represent an actual mass of air rotating at high speed compared to the air in front of the wing.

The vortices form 'vortex sheets' along the wing. Air is sucked into the vortex sheets and accelerated downward. As the airspeed in the vortex is high, the pressure is low. This low presssure on the upper surface produces lift.

From Low Aspect Ratio Wings at High Angles of Attack at adg.stanford.edu:

  ...the leading edge vortices, increase the wing lift in a nonlinear manner. The vortex can be viewed as reducing the upper surface pressures by inducing higher velocities on the upper surface.

Source: adg.stanford.edu

Basically, the vortices increase the lift from the baseline (potential flow) values, with the extra force being equal to the loss of leading edge suction associated with the separated flow in high angle of attack highly swept wings. This analogy gives the same result as before.

A Concept of the Vortex Lift of Sharp-Edge Delta Wings based on a Leading-Edge suction Analogy, Edward C. Polhamus, NASA Technical note D-3767

A major advantage of vortex lift generation is that it is effective at high angles of attack, over which the wings would normally stall. Actually, that Concorde used this method of lift generation is the reason for the high AoA during landing and its droop down nose.

Source: http://soliton.ae.gatech.edu

One thing to be noted is that vortex lift generation happens at high angles of attack or in case the wings are designed to generate separated flow (with sharp edges as in Concorde) in normal conditions. Otherwise the lift generation is by conventional means.

The same mechanism is responsible for lift generation in:

Strakes

By U.S. Navy photo by Mass Communication Specialist 2nd Class James R. Evans [Public domain], via Wikimedia Commons

Chines

Image from Effects of Vertical Tail and Inlet/Strake Geometry on Stability of a Diamond-Wing Fighter Configuration by Mitchell E. Fossum et al., accessed through http://enu.kz/

Canards

Source: forum.keypublishing.com


Would FAR 91.227, or any other regulation, forbid use of ADS-B-out in an unregistered ultralight? In the US, would FAR 91.227, or any other regulation or law, forbid use of ADS-B-out in an unregistered ultralight?  Could the N-number field simply be left blank, without violating any regulation or law?
What about a transponder with no ADS-B-out?
One possibly relevant detail: FAR 91.1(e) exempts ultralight vehicles from all of Part 91.

It looks like using ADS-B without any identifier would be contrary to 47 CFR 87.107(a), which requires all aircraft transmitters (with some exceptions, which don't include ADS-B) to include an identification, usually the registration.

§87.107   Station identification.
(a) Aircraft station. Identify by one of the following means:
(1) Aircraft radio station call sign.
(2) The type of aircraft followed by the characters of the
registration marking (“N” number) of the aircraft, omitting the prefix
letter “N.”
[...]
(3) The FAA assigned radiotelephony designator of the aircraft
operating organization followed by the flight identification number.
(4) An aircraft identification approved by the FAA for use by aircraft
stations participating in an organized flying activity of short
duration.

14 CFR 91.227 does allow for a "TSO-C154c self-assigned temporary 24-bit address" rather than the actual N-number but that part doesn't apply to ultralights anyway. It appears to be a reference to 87.107(a)(4) above.
Transponders are exempt from the requirement to broadcast identification, per 47 CFR 87.107(d).
Based on all that, and unless there's an FAA regulation about it (I couldn't find one), I'd say that a transponder is allowed on an ultralight (if you can operate it within the weight limit) but ADS-B is not.


Why would there be a NOTAM for an airport rotating beacon being on continuously? This NOTAM currently exists at Riverside airport:

!RVS 01/014 RVS AD AP ABN ON CONS 2001141700-2001291700

The rotating beacon is on continuously per this NOTAM.  It has nothing to do with the weather.

Why would an airport do this other than in IFR conditions during the daytime?

The general convention is that the rotating beacon is only on at night or during IMC. The airport or ATC can choose differently. It would not be the norm and probably should be pointed out to pilots approaching the airport. It would also help identify the airport if there is confusion with multiple nearby airports of similar size and structure.


Is there any common research model for supersonic transport? Is there any common research platform, like the Common Research Model of NASA for supersonic transport flight?

I assume that in aerospace industry, every company has his own research platforms depending on previous projects but was there any common model that companies shared for this purpose?

According to NASA here:

  This test case is an aircraft concept previously used as an optional
  case (LM1021) in the 1st Sonic Boom Prediction Workshop. This
  configuration is described in the following reference: John
  Morgenstern, Nicole Norstrud, Jack Sokhey, Steve Martins, and Juan J.
  Alonso, “Advanced Concept Studies for Supersonic Commercial Transports
  Entering Service in the 2018 to 2020 Period,” NASA
  CR-2013-217820,DOI:2060/20130010174. See NTRS Record. There is also a
  description in the following reference: John M. Morgenstern, Michael
  Buonanno, and Frank Marconi, “Full Configuration Low Boom Model and
  Grids for 2014 Sonic Boom Prediction Workshop,” AIAA-2013-647.


What daily commercial flight is the oldest / has been running the longest? Out of curiosity, what flight, currently still operating, has the earliest inception?

There are several ways to define this, and I expect available information will determine what definition is most useful. As an example, if a flight's inception date is the earliest date such that there has been a commercial flight on every day (or every week) between that date and today, what flight has the earliest inception date?

Also interested in a flight using the same aerodromes, or with the same airline, or even aircraft type.

According to the Georgia Encyclopedia one of the oldest flights operated by Delta was Love Field, Dallas to Birmingham, Alabama from 1929 up to 2000. Birmingham ist still served by Delta, but not from Love Field.

According to this the first flight from London to Schiphol was in May 1920. This route ist still in operation by KLM. But London at the time meant Croydon Airport.

On 27 May 1936 Aer Lingus made its first flight from Dublin to Bristol, while the route is also still in operation, the airfields changed. (wikipedia)

Take your pick.


What is the purpose of the black and white stickers on test aircraft? I want to ask what is the purpose of black and white stickers used on test aircraft.

The following is a picture:

I have seen variations of such stickers. Does anyone know what is reason for their use ?

They look very much like position markers to identify known points on the aircraft, for analysing video footage.  You see similar markers on crash-test dummies used in vehicle impact trials, for instance, and also in motion-capture in the synthetic movie industry (and in orthopaedics).