ATR Problem
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ATR Problem
When flying the ATR 42 the other day with a HT1000 GNSS in the cruise just coming up to an en-route hold encountered a strange problem...
The map display started to jump around from right to left (it appeared it was a very rapidly cycling map shift)
I changed back to conventional navigation, when looking at the GNSS all the data was clearly in error state our GS was showing some ridiculous figure.
Then the navigation display turned red and the EGPWS started to give just about every warning in the book - we were at the time flying in the mountains but well clear - and in VMC.
The CB was pulled for the EGPWS the GNSS continued to behave like this until after landing.. but then corrected itself and no fault could be found.
We did not get any warnings with regards to the status of the GPS - or RAIM warnings etc.
Approx 10 mins before the encounter we flew through some mod rain... so i was thinking maybe water in the antenna?
Any other thoughts on this?
PT6A
The map display started to jump around from right to left (it appeared it was a very rapidly cycling map shift)
I changed back to conventional navigation, when looking at the GNSS all the data was clearly in error state our GS was showing some ridiculous figure.
Then the navigation display turned red and the EGPWS started to give just about every warning in the book - we were at the time flying in the mountains but well clear - and in VMC.
The CB was pulled for the EGPWS the GNSS continued to behave like this until after landing.. but then corrected itself and no fault could be found.
We did not get any warnings with regards to the status of the GPS - or RAIM warnings etc.
Approx 10 mins before the encounter we flew through some mod rain... so i was thinking maybe water in the antenna?
Any other thoughts on this?
PT6A
Join Date: Aug 1999
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Hmm.
I'm not an avionics expert as far as antennae characteristics / water in the unitc goes. I was an intructor on the HT-1000 as embodied in the ATR, however I haven't flown it for many years.
Haven't heard of anything like that before. Yes, I've heard of the odd map shift. If it was having difficulty in receiving the satellites then yes its ANP could degrade, but you'd have thought you'd have received an UNABLE RNP message.
Did you happen to note what was happenning to the ANP?
pb
I'm not an avionics expert as far as antennae characteristics / water in the unitc goes. I was an intructor on the HT-1000 as embodied in the ATR, however I haven't flown it for many years.
Haven't heard of anything like that before. Yes, I've heard of the odd map shift. If it was having difficulty in receiving the satellites then yes its ANP could degrade, but you'd have thought you'd have received an UNABLE RNP message.
Did you happen to note what was happenning to the ANP?
pb
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Hi Pitbull,
No I did not notice the actual RNP value as I head to enter the hold manual and had been planning on the FMS doing it.
But yeah there was no unable RNP message on the scratch pad or the message on the PFD directing me to the scratch pad.
I have seen the unable RNP message on this aircraft on a previous flight so I know it is functioning.
But yes it was very odd! The display was jumping back and forth at a very high rate of knots!
Had this been a dark and stormy night when all the EGPWS warnings went off would if resulted in a go-around and the potential for confusion without a doubt.
I'm flying the same aircraft tomorrow so I will see how it is acting.
PT6A
No I did not notice the actual RNP value as I head to enter the hold manual and had been planning on the FMS doing it.
But yeah there was no unable RNP message on the scratch pad or the message on the PFD directing me to the scratch pad.
I have seen the unable RNP message on this aircraft on a previous flight so I know it is functioning.
But yes it was very odd! The display was jumping back and forth at a very high rate of knots!
Had this been a dark and stormy night when all the EGPWS warnings went off would if resulted in a go-around and the potential for confusion without a doubt.
I'm flying the same aircraft tomorrow so I will see how it is acting.
PT6A
