Questions tagged [sensors]

Questions about various sensors used in aviation, both on aircraft and ground equipment.

Filter by
Sorted by
Tagged with
37 votes
2 answers
65k views

How does an alpha (AoA) vane work?

The alpha vane (also called AoA vane) is an external probe used to measure the angle of attack. I have been trying to understand how exactly it works, but I can't find any clear explanation or ...
asheeshr's user avatar
  • 1,614
18 votes
1 answer
4k views

What is this device protruding from the rear of this 787?

While looking at the photos from this question I noticed a small protrusion from the side of the plane. You can see it in the photo: and in the diagram from l@aeroalias answer: In the diagram it ...
TomMcW's user avatar
  • 28.4k
22 votes
2 answers
8k views

What is this 'ball' in front of the cockpit of some fighters, e.g., an Su-57?

What is the lump/ball thing visible below and to the left of the canopy in this image of a PAK FA (which became the Sukhoi Su-57), and what is it for? It's also seen on other fighters. Image source
anonymous's user avatar
  • 3,564
16 votes
2 answers
4k views

How is fuel mass measured in airliners?

Large airliners display the amount of fuel in each tank as a mass (usually in kg or lbs) and not as a volume. This makes sense since mass is important for weight&balance considerations and the ...
Bianfable's user avatar
  • 55.4k
10 votes
3 answers
628 views

Is it common for automated control systems to use non-redundant sensors?

While reading an article about the Lion Air Crash with a Boing 737 Max 8, I was very surprised by the following paragraph: In designing the 737 Max, Boeing decided to feed M.C.A.S. with data from ...
user avatar
7 votes
1 answer
728 views

Why are the positions of an aircraft's angle-of-attack vanes dependent on airspeed?

According to this answer to an earlier question of mine, the positions of the angle-of-attack sensor vanes on the A330/A340 are dependent not only on AoA, but also on airspeed (and, according to @ymb1'...
Vikki's user avatar
  • 28.3k
5 votes
1 answer
2k views

Will an Airbus A320 plane go into an unrecoverable nosedive and crash if a single angle of attack sensor fails, like on Lion Air JT610?

For example, has an Airbus gone from cruise flight into an automated unrecoverable nose dive until it hit the ground because an AOA sensor failed in flight? Moreso, are there any cases of an AOA ...
Willy A's user avatar
17 votes
4 answers
3k views

How does the Guardian counter-MANPADS system work?

I came across this picture of a FedEx McDonnell Douglas DC-10 equipped with an anti-missile defense system. (wikimedia.org) According to the picture description: FedEx became the first U.S. ...
shortstheory's user avatar
  • 3,976
9 votes
2 answers
4k views

How do tyre pressure sensors in aircraft work?

I am specifically interested in the sensors used on the B777 and B787.
Pritam's user avatar
  • 548
9 votes
1 answer
10k views

How many AOA sensors does the 737 MAX have?

How many AOA sensors does the 737 MAX have? Given that it's reported in the media, that one faulty AOA probe activated the MCAS on the Lion Air flight, I was wondering if anybody also knows how an ...
user33651's user avatar
  • 1,021
7 votes
3 answers
3k views

What types of fuel quantity sensors are used in an aircraft? How do they work?

Can you explain the different types of fuel quantity sensors used in most recent aircraft? Are ultrasonic tank sensors used these days? How does an ultrasonic sensor work?
Pritam's user avatar
  • 548
6 votes
2 answers
3k views

How does a fuel density sensor work? (densitometer, cadensicon)

While some fuel volume sensors use ultrasonic measurements this answer to How is fuel mass measured in airliners? says: The FCOM lists the sensors involved in this measurement: The FQI system ...
uhoh's user avatar
  • 5,808
5 votes
2 answers
5k views

What is the difference between IMU (Inertial Measurement Unit) and AHRS (Attitude and Heading Reference System)?

According to online sources like wikipedia the difference belies on the addition of an on-board processing system (I assume it means a microcontroller) which outputs already processed data and not ...
A. Fenzry's user avatar
  • 403
4 votes
2 answers
7k views

How does a pilot know if he has headwind, tailwind or crosswind?

While in cruise, without GPS how does a pilot know the wind direction? The airspeed sensors only register forward speed. Is it a matter of reaching waypoints sooner or later? And if flying on a ...
TomMcW's user avatar
  • 28.4k
3 votes
1 answer
394 views

Can a laser Doppler anemometer be used to measure airspeed?

Could this be used in place of or in addition to a pitot-static system?
TomMcW's user avatar
  • 28.4k
18 votes
4 answers
4k views

Why is not every airplane equipped with 3 angle-of-attack sensors?

For critical systems, redundancy is built into the system. It is common knowledge among designers/architects to have three different inputs so in case one is faulty, input from the remaining two can ...
Regmi's user avatar
  • 935
16 votes
3 answers
3k views

Do modern airliners have oxygen sensors in the cabin?

I know that airliners have pressure sensors to check the cabin pressure, and thus check if we can breathe (and get enough O2) inside it so we don't get hypoxia. But that got me thinking: Is there any ...
Gabriel Brito's user avatar
15 votes
1 answer
2k views

What were the advantages of the L-1011 AoA sensor design?

The Lockheed L-1011 had an unusual type of AoA sensor. Instead of the usual vanes it used a tube with two rows of holes in it about 90° apart. A diaphragm sensed the pressure differential between the ...
TomMcW's user avatar
  • 28.4k
14 votes
1 answer
3k views

What are these sensors on the Night Stalkers' Chinook MH-47G?

What are these sensors (or lights) on this heavy assault Chinook MH-47G of the US 160th Special Operations Aviation Regiment, "Night Stalkers"? Source, picture by Russell Hill This regiment was the ...
mins's user avatar
  • 71.8k
13 votes
2 answers
4k views

Why are the angle-of-attack sensors on most airplanes mounted on the forward fuselage rather than at the wing roots?

A source of reliable angle-of-attack information is important for airplanes, as flight at an excessively-high angle of attack can cause the airplane to stall, which is generally considered to be an ...
Vikki's user avatar
  • 28.3k
8 votes
3 answers
2k views

Why do aircraft stall warning systems use angle-of-attack vanes rather than detecting airflow separation directly?

Stall warning and protection systems on essentially all aircraft work by using several hinged vanes on the side of the fuselage (usually at least three, and preferably more), which align themselves ...
Vikki's user avatar
  • 28.3k
5 votes
4 answers
8k views

How are pitch angle and pitch rate measured in an airplane?

What equipment or method is used to obtain measurements of the pitch angle (θ) and pitch rate (q) during flight? Edit: I am asking about how the aircraft systems sense these quantities
Mateus de Freitas's user avatar
4 votes
2 answers
6k views

How would the Airbus A320 PFD respond to failure of all pitot and AOA sensors?

In theory, if all 3 pitot tubes and all 3 AOA-sensors would fail simultaneously for a period of time, could the PFD still deliver correct roll angle and horizontal displays? How would the plane ...
Horizontal Vertikal's user avatar
3 votes
3 answers
381 views

Is there a practical use of streaming data received from meteorological sensors installed on aircraft?

I am not the practitioner in the field of aviation, and my knowledge is mainly theoretical. Therefore I would be happy to get a feedback from practitioners on the following topic: I was reading about ...
Glicker's user avatar
  • 31
2 votes
1 answer
385 views

How are AOA sensors tested after working on them?

If a maintenance or replacement has been done for an AOA sensor, would the mechanic be able to test if the sensor now works correctly? Can such a sensor be tested on the ground? If there is no ...
h22's user avatar
  • 12.1k
1 vote
1 answer
376 views

How many Angle of Attack sensor vanes should a commercial passenger airliner have? [closed]

The ill fated MAX of recent news had 2 angle of attack vanes, with the MCAS computer picking the worst one. It seems a "software patch" may not be the only improvement option available. Sensible ...
Robert DiGiovanni's user avatar
1 vote
1 answer
836 views

Why does an ADIRU 1 failure disable all functions of the A330/340’s GPWS - even those not requiring ADIRU data?

Among the many (many many) aircraft systems degraded or rendered unavailable to the flightcrew of QF72 as a result of a partial intermittent ADIRU 1 (Air Data / Inertial Reference Unit 1) failure, the ...
Vikki's user avatar
  • 28.3k