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A question was asked on VAF this morning:
"What does your EFIS NOT display if you lose pitot /static input (for example, blocked due to ice). If the input source is from VHF rather than GPS (you're on an ILS), do you lose attitude? How does the screen display lack of pitot?"
I'm not sure I can fully answer this question, since I'm not flying behind an AFS EFIS yet. But it did peek my curiousity. So what happens when a pitot source becomes unavailable?
thanks,
bob
The AHRS will still work fine and you will still have attitude information, without Pitot and static you will not be getting reliable airspeed and altitude data.
How about altitude - any reversion to GPS altitude if the static line or pressure sensor becomes inop?
I suspect that there is no way to know that it has iced up. If it leaks it will read cabin altitude and if it is blocked it will read the last altitude.
The SV, terrain warnings, altitude above ground , and runway drawing is all done using GPS altitude.
Hi Bob,
The scenario you are describing is the classic "unreliable airspeed" situation. It makes no difference whether you are flying behind an EFIS or steam driven instruments. The readings of some or all of your instruments using the pitot/static system will be erroneous. Which instruments are affected depends on whether the pitot or static system is blocked or leaking.
For example, if your pitot tube is blocked in the climb by an an insect or debris from a bird strike, the pressure trapped in the system at the time of impact will be frozen. If you level off at the height of impact, the IAS at the time of impact will be indicated regardless of the speed you fly. If you climb the indicated speed will increase as the static pressure decreases and obviously the opposite will happen if you descend. Your altimeter and VSI will not be affected in this case.
Recognition of unreliable airspeed is vital, especially in IMC. It is important to memorise certain pitch and power settings to mantain level flight at certain speeds and also the pitch and power settings for climbs and approaches at given speeds. Here the accurate attitude indication from an EFIS with SV can be a great help.