ASI Failure in flight

 

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Today I was flying with my flying partner Josh to Granada and back, Josh was to fly to Granada and do a procedural ILS landing and I was to fly back and do an ILS at Jerez followed by a single-engine NDB approach and circle to land.

The day was quite cloudy and climbing out from Runway 20 the cloud was as low as 900feet which meant we were straight away into instrument conditions even without the screens up.

IMC Conditions

The temperature was very low and climbing through the cloud up to FL100 the temperature dropped to –9C, this meant we had a lot of moisture at a very low temperature and we were flying over high-ground.  The high ground meant that we could not descend but we did deviate from our planned track quite a few times because of towering cumulus clouds.

When we were about 15miles from the Granada beacon, Josh noticed that the aircraft was struggling to maintain its airspeed and that the manifold pressures were increasing.  He rightly reduced the manifold pressures so that they did not exceed their limit for the set engine speed, but then the airspeed started to reduce even more.  We slowly watched the ASI reduce from 145kts down to 110kts which is where I started to feel a bit uncomfortable, although looking at the KNS80 it still said that our groundspeed was 185kts.  This meant that we either had an ASI fault, or that there was a huge tailwind and that we were getting dangerously close to the aircraft stalling out of the sky in an area where our minimum safe altitude was still over 7000ft.

Eventually Josh turned off the autopilot and decided to pitch nose-up 40deg and stall the aircraft backwards into the ground…  only joking.  No, he pitched up a couple of degrees, set fast cruise power and told Malaga approach that he was going to head north where there was clear air and he would be able to better assess the “technical problem” he had (Spanish controllers do not understand anything more than technical problem).  As we headed out towards the clear sky the ASI was starting to slow down towards 70kts, this is slower than the speed we would normally land the aircraft at and if it was true we should have had a very high nose-up attitude but according to the attitude indicator this was not the case.  One thing that was also concerning was that if the ASI had failed, had the Altimeter failed as well and therefore we had no idea of speed or height.  This was the main reason we headed for clear sky because we could not descend due to MSA and we could not climb either because the Operations Manual prohibits us from flying about FL100.

After another 10minutes the ASI was suddenly reading zero and at this point we knew we had an ASI failure.  We broke out of cloud and could clearly see that we were still very high up and therefore an altimeter failure was unlikely.  We decided to make a turn for home and get the problem sorted out, our suspicion was either moisture in the pitot lines or a pitot-heat failure.

As we started to descend towards Jerez we needed to use the icing boots quite frequently to shed the ice from the wings of the aircraft.  I managed to capture a video of this, but you have to watch quickly as we are flying at around 200mph which means the ice flies off quite fast!

With about 20minutes to land we had used the alternate static source and opened the pitot drains to try and clear any blockage that may have occurred, it was then that the ASI suddenly sprung back to life which meant a much easier and less eventful landing some 2 hours after we had first departed.

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~ by globalste on January 27, 2012.

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