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1. 01:39 PM - Re: Re: ADS-B Receivers (Bill Watson)
2. 04:48 PM - Re: ADS-B Receivers (Bob Turner)
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| Subject: | Re: ADS-B Receivers |
Here's some more jacket for the flak...
I recently experienced a partial pitot blockage while in IMC. It was
one of those all too rare moments when I was hand flying the plane. My
GRT HX EFISs presented a perfect attitude display. So perfect that I
did not notice the airspeed decay that was quite visible on the airspeed
tape. With the engine running normally it was easy flying the attitude
indication.
However when I switched on the Trutrak AP I noticed the "AS" flag as
the AP commanded a dive to prevent a stall. I quickly switched it off,
recovered, then tried it again with the same result. I finally asked for
vectors to the nearest airport which incidentally led me to declare an
emergency. The plane was easily flown using pitch and power in IMC and
VMC conditions to an uneventful landing (with trucks rolling).
It took some effort but I finally cleared out the insect debris clogging
my Gretz pitot.
The fact that the GRT HX EFIS maintained it's attitude display
independent of airspeed made this a non-event. If my attitude
indication had caused me to gradually hand fly the plane into a dive or
other unusual attitude things would have been a bit tougher to sort out
and recover from.
This was a particularly perverse partial pitot blockage. Further
'testing' showed that In fact, the blockage occurred only when flying
in wet conditions (wet cloud, mist or rain). Apparently the insect
debris was absorbent and would swell up instantly with the slightest bit
of moisture. Then it would unblock itself after 10 or 20 minutes of dry
conditions. This means everything would be fine until wet IMC was
encountered.
In my particular setup the outcome was never in doubt and I'm glad the
NTSB didn't have to try to sort this one out.
Bill "happily flying his kitchen sink of a panel" Watson
BTW, I'm flying GRT HX, Trutrak AP and Navworx ADSB - It all works great!
On 8/31/2015 3:46 PM, Bob Turner wrote:
> Okay, now flak jacket on. IMHO the Skyview is only marginally acceptable for
actual IMC, because its attitude solution (horizon) requires accurate airspeed
data. Dynon recognized the issue, and a software upgrade attempts to flag bad
airspeed and revert to gps data. However, there is at least one report of a partial
pitot blockage, where the blockage was bad enough to generate incorrect
horizon data, but not bad enough to trigger the switch to gps data.
> I believe but am not certain that the turn coordinator bars continued to work
properly, so a really good pilot could squint and watch those bars while ignoring
the horizon. And/or, throw the switch to put the autopilot into stand alone
mode and use that. There are options, which is why I said "marginally". But
you must be aware of the possibility.
>
> --------
> Bob Turner
> RV-10 QB
>
>
Message 2
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| Subject: | Re: ADS-B Receivers |
Thanks for reminding me that if the indicated airspeed gets too low, the autopilot
is NOT an option. I have the Trio but it has the same feature as the TT, it
will dive the airplane to prevent flight below indicated stall speed.
--------
Bob Turner
RV-10 QB
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http://forums.matronics.com/viewtopic.php?p=446706#446706
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