Air France 447 is a powerful example of what a serious situation unreliable air data indications can be if not handled properly by a crew. Still, whether crews are properly trained or use that training, unreliable air data presents a dangerous situation. Pitot tubes are fallible devices susceptible to errors caused by environmental factors such as ice crystals. With this in mind, what technical alternatives to pitot static systems exist or might be developed that are more accurate and less prone to interruption?
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3$\begingroup$ Although used for stealth, and susceptible to water even in its liquid form, here's another system $\endgroup$– NathanGJan 9, 2017 at 2:28
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3$\begingroup$ Of course, any novel alternative type of sensor may also be susceptible to problems due to ice or some other conditions we don't yet understand. You'd potentially be replacing a known risk with some unknown risks. The BEA report on AF447 did not mention or recommend looking for alternative sensor technologies - it discussed the use of other types of pitot-tube. $\endgroup$– RedGrittyBrickJan 9, 2017 at 10:11
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$\begingroup$ @RedGrittyBrick That doesn't mean they couldn't be used in conjunction with each other. The article Aeroalias linked points out that the failure modes of the optical system were different from those of pitot tubes. Therefore they would be a good complement to each other $\endgroup$– TomMcWJan 9, 2017 at 19:53
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2 Answers
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A number of systems are under development- most are optical systems- determining airspeed using LiDAR. NLR, for example has developed an Optical Air Data System for this purpose:
The developed system applies the LiDAR technique to measure air speed in four different directions. The aircraft’s TAS (True Air Speed), AOA (Angle Of Attack) and SSA (Side Slip Angle) are calculated from these speed measurements.
Other systems are in prototype stage- including a photonic system that is based on back scattering of light, but none of them are yet operational.
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While there are different possibilities to measure pressure (e.g. pressure sensitive paint), all can be influenced by environmental factors.
So the question might be: What is the best trade-off between cost of the sensor(s) and reliability of the whole measurement system?
One solution might therefore be to compare different sensor readings (Air speed, control surface position, weight, altitude etc. ) and compare those with a (machine learned) model of how the aircraft should behave. This would enable a algorithm to decide if a sensor does not provide realistic data and should therefore not be trusted any more.
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$\begingroup$ How does pressure sensitive paint react to a change in pressure? $\endgroup$– user7241Dec 13, 2017 at 3:44
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$\begingroup$ It actually reacts to a change in the partial pressure of one air component (oxygen) with a change in color. So one could have a small patch of glass which is looked (sensor) at from the inner side. $\endgroup$– rul30Dec 13, 2017 at 5:26