Started plane and taxied for a run up after cleaning plugs, there is no indicated airspeed under 20 Kts and occasionally a warning would pop up saying. GPS ASSIST. I have two AHRS and two screens. Afraid to go flying n case it happens in the air at higher speeds. Any thoughts?
No IAS taxiing under 20 Kts
- Thread starter rtairey
- Start date
Sounds like a daft question but what was the windspeed and were you going downwind or into wind?
We've seen this occasionally when back tracking a runway then realised we were going downwind and there was no actual airspeed to indicate!
GPS Assist is, if I remember correctly, giving you a ground speed - I presume as the kit is sensing movement but without an airspeed showing.
We've seen this occasionally when back tracking a runway then realised we were going downwind and there was no actual airspeed to indicate!
GPS Assist is, if I remember correctly, giving you a ground speed - I presume as the kit is sensing movement but without an airspeed showing.
Thanks, I really expected some answers for me to check obvious thing such as this and whether I had the pitot cover on ( it wasn't). I am expecting this to be something obvious that wasn't to me today. I did consider wind, but I taxied on multiple runways and into the wind. This is the first time I have seen this. I also had not done any work on the plane lately. Looks like the heated pitot is open and not plugged, but hard to see way in. I have been flying a lot lately, plane has not been idle.
mmarien
Murray M.
IAS doesn't register until about 20 kts. 20 kts is pretty slow because analog IAS gauges don't usually register until about 40 kts.
GPS ASSIST is normal behavior. If the pitot fails then Skyview will display the ground speed and GPS ASSIST. You can make it happen anytime with a ten knot wind. If you taxi at ten knots into a ten knot wind your IAS will indicate 20 kts. Turn around and taxi at 10 knots and the IAS will be zero. At 20-30 kts it will still be zero but GPS ASSIST will kick in and display the ground speed as IAS.
I get GPS ASSIST all the time backtracking with a strong tailwind if I let the speed build too much.
GPS ASSIST is normal behavior. If the pitot fails then Skyview will display the ground speed and GPS ASSIST. You can make it happen anytime with a ten knot wind. If you taxi at ten knots into a ten knot wind your IAS will indicate 20 kts. Turn around and taxi at 10 knots and the IAS will be zero. At 20-30 kts it will still be zero but GPS ASSIST will kick in and display the ground speed as IAS.
I get GPS ASSIST all the time backtracking with a strong tailwind if I let the speed build too much.
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GPS assist appears when:
1) You have had airspeed at some point on that power cycle. Doesn't need to be now, a single jump >20 knots even once for 1/16th of a second will do it. A single gust of wind.
2) You have GPS ground speed greater than some low number that I forget
So, all this means is that your airspeed went above 20 knots once and you are moving. It's nothing to be concerned about. In fact, it would go away the instant airspeed started reading on your takeoff roll.
Also, unless your next flight is straight into IFR, this isn't something to be worried about. GPS assist works 95% as well as standard mode, it's just that your redundancy is gone, so on a VFR flight it's no big deal.
1) You have had airspeed at some point on that power cycle. Doesn't need to be now, a single jump >20 knots even once for 1/16th of a second will do it. A single gust of wind.
2) You have GPS ground speed greater than some low number that I forget
So, all this means is that your airspeed went above 20 knots once and you are moving. It's nothing to be concerned about. In fact, it would go away the instant airspeed started reading on your takeoff roll.
Also, unless your next flight is straight into IFR, this isn't something to be worried about. GPS assist works 95% as well as standard mode, it's just that your redundancy is gone, so on a VFR flight it's no big deal.
Carl_Froehlich
Active Member
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A simple and exceptionally accurate method of verifying airspeed read out is it use a manometer. These are simple to build - requiring not much more that some tubing and a vertical board. Here is one link:http://www.iflyez.com/manometer.shtml
Here is the PDF file for the airspeed scale:http://www.iflyez.com/Manometer.pdf
This can also be used to chase down pitot/static leaks. For static leaks remember to run the vacuum on both the pitot and static ports so you do not over scale the airspeed instrument. Do this before your pay for the pitot/static test and save yourself a lot of cash by fixing the leaks before the test. This is a well used test rig in the local airpark.
Here is the PDF file for the airspeed scale:http://www.iflyez.com/Manometer.pdf
This can also be used to chase down pitot/static leaks. For static leaks remember to run the vacuum on both the pitot and static ports so you do not over scale the airspeed instrument. Do this before your pay for the pitot/static test and save yourself a lot of cash by fixing the leaks before the test. This is a well used test rig in the local airpark.