Dear Fellow Pilots,

I’m a newbie to and require your advice regarding major fuel pressure problems. The serial number of my Pipistrel Virus SW 100 is “355 VSW 100” and the Rotax 912 ULS engine serial number is “6776233”.

Flying in Thailand, I had various low fuel pressure warnings during 2 flights and 1 flight with engine-out due to no fuel pressure:

1. Low fuel pressure warnings: Both flights had a similar profile. Descending from 11,500 feet at a rate of 1,000 feet/min. Low fuel pressure warnings came on and went off after about 1 minute at 7,500 and around 4,000 feet. Then no more warnings until I reached 2,000 feet with warnings coming on again. The fuel pressure warnings were between 0.14 bar and 0.03 bar. During the time of the fuel pressure warnings, the engine seemed to run with a slightly limited capacity but not rough. Due to high non-standard temperatures in Thailand, density altitude is around 2000 to 2,500 feet higher than pressure altitude.

2. Engine-out due to no fuel pressure: During a recent x-country flight, I was flying straight-and-level at 7,500 feet for about 20 minutes. Then the low fuel pressure alarm came on. After about 10 seconds – with the last fuel pressure reading at 0.03 bar – the engine stuttered and then quit. I immediately put the plane on best glide speed. Tried to restart without success. Whilst gliding, I entered the clouds and was in complete IMC. No ground reference whatsoever. Flew the plane based on instruments and tried to restart again. No success. Finally, after the 5th attempt to restart, the engine started. I was still in IMC, stabilized the plane at 6,500 feet, and turned on the Auto Pilot. For the lack of better alternatives, I decided to continue flying in IMC (I’m IFR-rated but not current). I made heading and altitude changes only via the AP. Landed safely.

During the incident, I was flying mainly VFR-on-top in mountainous area of 3,000 to 5,000 feet about 50 NM from the next airport. Just glad the engine restarted at an acceptable height.

Afterwards, I test-flew the Virus for 2 hours at an altitude of 2,000 to 3,000 feet. No problems whatsoever but I was rather apprehensive and it was no fun. The fuel pressure problems seem to materialize at medium to high altitudes.

My Virus still has the original fuel pump from 2010 (P/N: 892542. The previous owner, based on a service bulletin, bought the recommended new fuel pump but it showed false readings. He then reinstalled the original fuel pump and never had a problem (so did other pilots I know who had experienced the same problem).

Engine-out in IMC and mountainous area can be quite a sobering experience and I do not wish to repeat this. Until I can solve the fuel pressure problem, I decided not to fly the Virus again. Right now I feel unsafe flying my plane.

I’ve ordered the recommended fuel pump based on the Rotax Service Bulletin (P/N: 893115) and it will be installed during the next two weeks. As a back-up, there is now also an electric pump (Facet).

I’m still very interested about the potential causes for low fuel pressure warnings and, especially, regarding the engine-out due to no fuel pressure. Any advice – especially how to avoid these issues – would be very much appreciated.

Amongst my flying friends who are quite knowledgeable when it comes to technical issues, one possible explanation was “vapor lock”. I’m a non-technical person and rely on advice.

Many Happy Landings,

Gottfried Thoma (thomago)
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