Do the airplanes depend on pitot tubes only for speed measurement?
May 1st, 2010 | by admin |Do they have speed sensors based on GPS? Loosing pitot tubes may cause an accident?
Rob T has a good answer.
The air speed indicator is supplied from the pitot tube, and also the static pressure vents. The ASI is continually comparing the pressure in the pitot tube to the outside air pressure. This is how come it actually shows indicated air speed, which is a speed greater than the actual speed over the ground, even though it may read the same as a ground speed indicator might read if you had one to compare.
There are backups should the ASI malfunction, there is at least 1 other ASI in all commercial aircraft. GPS can also give valuable information.
I think you are asking this question because some person suggested in the media, the pitot was at fault on the Air France disaster recently.
It is ridiculous to suggest a pitot was at fault. Any pilot would have realised that this was not the case, and gone to backup systems. Whoever released that "information" was only looking for publicity…. there is no way, unless the flight recorder is located and useable, that anybody will be able to say what caused that crash….
3 Responses to “Do the airplanes depend on pitot tubes only for speed measurement?”
By Mark G on May 1, 2010 | Reply
Pitot tubes measure air speed, while other devices you mentioned such as GPS measure ground speed.
So if you have a ground speed of 100knts and a tail wind of 30 knts your air speed is 70 knts… Air speed over the wings is what matters regarding lift.
References :
By Rob T on May 1, 2010 | Reply
Pitot tubes don’t actually measure speed, they measure pressure difference. In fact pressure difference is exactly the information you need for safe flight, because the aerodynamic forces also depend on pressure difference.
Pitot tube "Air speed indicators" actually show a quantity called indicated air speed (IAS), not true air speed. The two speeds are only the same at zero altitude and standard air pressure. But IAS is the important quantity you need to know, because at different air pressures and temperatures the important parameters like the aircraft stalling speed are at the same IAS but different true air speeds. Using IAS means you don’t have to think how to interpret the true air speed at different altitudes and in different weather conditions.
Pitot tubes are very simple and reliable devices, provided they don’t ice up.
Of course a modern passenger plane will have multiple air speed sensors, and also GPS and other radio based navigation systems that give true ground speed.
References :
By Technobuff on May 1, 2010 | Reply
Rob T has a good answer.
The air speed indicator is supplied from the pitot tube, and also the static pressure vents. The ASI is continually comparing the pressure in the pitot tube to the outside air pressure. This is how come it actually shows indicated air speed, which is a speed greater than the actual speed over the ground, even though it may read the same as a ground speed indicator might read if you had one to compare.
There are backups should the ASI malfunction, there is at least 1 other ASI in all commercial aircraft. GPS can also give valuable information.
I think you are asking this question because some person suggested in the media, the pitot was at fault on the Air France disaster recently.
It is ridiculous to suggest a pitot was at fault. Any pilot would have realised that this was not the case, and gone to backup systems. Whoever released that "information" was only looking for publicity…. there is no way, unless the flight recorder is located and useable, that anybody will be able to say what caused that crash….
References :