Gipsy Major engine problems prompt CAA action

Owners of aircraft powered by Gipsy Major engines are being contacted by the CAA after episodes of rough running engines and engine failures.

Analysis by the CAA shows an emerging trend of problems with the Gipsy Major engines. The use of 100LL Avgas fuel in these engines could be causing reliability problems particularly with cylinder heads, valves and valve seats.

Tiger Moths, Chipmunks and Austers are amongst the aircraft fitted with Gipsy Major engines. Photo (top) of a dh82 Tiger Moth by Tony Hisgett.

Owners of affected aircraft are advised by the CAA to ensure routine checks on these engines are carried out by a maintenance organisation or person experienced on the engine type.

Checks should also be carried out if incidents of low compression are noticed in the engine when turning the propeller by hand, or if the engine is found to be running rough.

Owners are also advised to ensure they are using the most appropriate fuel at all times – UL91 is the most appropriate, says the CAA.

As well as contacting all owners of affected aircraft types listed on the national aircraft register, the CAA is also issuing guidance material to continuing airworthiness maintenance organisations.

CAA Poster


  1. I have reason to believe that the author of this alert from the CAA is not an Airworthiness representative, and is not even an engineer. To tell owners and operators of Gipsy powered aeroplanes to check their engines when they are losing compression or rough running is not exactly startling advice. It is rather akin to warning farmers to feed their cattle when they get hungry. I wonder if the man even was aware, when he wrote this alert, that some Gipsy engines have bronze cylinder heads, but most have aluminium heads. It is well known that the life of a bronze head is reduced by the use of 100LL, and most owners of such aircraft will know when the engine loses compression it is time to service the cylinder heads. If this is not happening, engineering oversight is the problem – nothing more – and there is no difference between a Gipsy or a Lycoming engine which loses compression.
    Aluminium heads do not suffer in the same way, and 100LL fuel is absolutely acceptable for these engines and available Europe-wide, if not Worldwide, unlike UL91 which is often very difficult to come by. It would be interesting to know if this man consulted Deltair or VINTECH before bursting into print.
    Imagine the implications of a court case against a pilot who had an accident when it was discovered that the aircraft had 100LL fuel in the tanks against the CAA’s ‘expert’ advice, even if there had been no loss of power.
    Is this the sort of responsible monitoring we need from the Authority?

  2. Agree wholeheartedly, Robin. Most Tiger owners these days are more aware than of old, concerning the problems with Gypsy 1s caused by modern fuels.
    Recently had cause to re-read AAIB Bulletin, 1/2006, Pages 85 -88.
    This provides quite a good historical, technical analysis of fuel grades and oil contamination from a chap who, in those days, had mugged up and knew what he was talking about. ………and who he was talking to !!

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