39 - Engine Power Losses on Takeoff

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Dear Jim,

Thank you very much for your kind and encouraging words, but I must point out that my recent e-mail about the inadvisability of taking a suspect engine into the air was most definitely not triggered by any recent accident.

The most recent of the accidents I referred to was around six months ago.

My interest in this topic was triggered by one of about 200 GA accident reports I read last week. British investigators thoroughly examine all aircraft accidents and produce a monthly bulletin, which is sent to interested parties (myself included). Ten of these were waiting among a three-foot pile of mail on my doorstep here in England. I try to read them all, and am particularly fascinated by those that should never have happened.

As well as the three accidents I mentioned, I said there were two SABC aeroplanes that flew with seriously under-performing engines, despite their pilots knowing before flying that there was a problem. Since I wrote my e-mail, I have remembered a third similar occurrence.

One of these highly unwise pilots was myself, so let me tell you more:

I was doing some test flights on a good aeroplane that recently had fitted a second-hand Jabiru engine. The previous owner said it was a 'great little motor, low hours, perfect condition, never gave me any trouble, it was owned by a little old lady who only used it to run to the shops etc, etc....'

This engine seemed to run fine on the ground, and gave quite enough power for a few tentative hops, so I took it into the air. Very bad move.

The aeroplane would barely climb, and I made a very scary low-level fright of two minutes and forty three seconds, every second of which I clearly remember (at least, I remember those in which my eyes were actually open which, I have to admit, was not all of the time).

We then got a local expert to look at the carburettor. He found a perished O-ring and a couple of other small problems. I was in a hurry to get away to France, where I was due to give a talk on aerobatics, and had already delayed my departure to get this job done, so off I went on another flight.

THAT WAS WHERE I WAS VERY STUPID.

This flight lasted a little longer, because I had to fly around so many trees. I don't remember a great deal of it, but I do clearly recall promising earnestly to go to church next Sunday if I got down alive.

WHAT WE OBVIOUSLY SHOULD HAVE DONE, on establishing that the carburettor had a perished O-ring and one mal-adjustment, was to have the carby fully and thoroughly overhauled, and re-adjusted, with new internal components wherever there was any doubt about their condition. This would have taken time and cost some money, but the time and cost were nothing in comparison to the time and cost spent re-building the aeroplane.

Sure enough, when the carby was fully stripped, two more perished O-rings were found, plus some other minor mal-adjustments that had probably been made to compensate for these dodgy O-rings. When the carburettor was re-fitted, it was also seen to have been slightly tilted to one side.

At that time, I had not known this was a common problem with Bing carburettors on Jabiru engines. I discovered this from another British accident report. And this, of course is why the British so thoroughly investigate these accidents: to find out what caused them and ensure everybody else is informed, so that nobody else makes the same mistake.

Please be warned: if you have a Jabiru engine, it is very important to ensure the carburettor is on dead straight and square. Engine failures and severe power losses can occur when it is not. I do not know if the same applies to the Bing carburettors on Rotax or other engines, but it seems a good idea to check them anyway. Any carby should be on straight and true, since the fuel level in the float bowl might be affected.

Much more importantly, please do not fly when you have the slightest suspicion about the condition or power output of your engine.

It might take a very long time and cost a lot of money to establish the causes, but as I said before, it could take much longer to fix your aeroplane if you try to fly it like that.

Old aviation saying: It is far, far better to be on the ground wishing you were in the air than......

Bob "Bob the Grim" Grimstead
SABC Safety