Loss of Power

Aeroplane engines are generally reliable beasts.

Bear with me on the basic physics at play before the story starts.

Piston engines twins are split into two types, those with ancient thirsty old engines made by the likes of Lycoming & Continental, then those more modern ones which run on diesel and made by manufacturers such as Thierlert. There are of course exceptions like the fine Tecnam twin with its Rotax engines, but they are currently just finding their way into the training fleet in the UK and don’t have the payload of the bigger twins.

The bigger heavier piston twins are almost entirely made up of those fitted with the avgas loving, low revving units as found in the Chieftain I fly at work. Large capacity solid blocks that last and last, as long as they are not maltreated.

Pilots are trained to deal with engine failures almost from the very start of their training. Initially on single engined types where the only option is to adopt a gentle glide towards the earth and pick a suitable field to land in; carried out correctly this gives a very good chance of survival should the worst happen.

When pilots move onto twin engined aeroplanes they are taught what to do when one engine fails. Should both fail at the same time, adopt that technique learned for single engined aeroplanes but expect to arrive faster and sooner!

There are all sorts of aerodynamic and physical forces at play when a twin loses one engine. This can be googled and researched elsewhere, but basically the end effect is that the aeroplane will struggle to climb away from the ground effectively unless dealt with promptly and in the correct manner.
This can be even more difficult in hot weather as the air is less dense (thinner) meaning the engine develops less power. This affects both acceleration and rate of climb (vertical speed away from the ground). Lose one of the engines and that rate of climb will diminish still further! A pilots favourite weather for take off therefore is cold crisp air.

When operating from hot countries there is an allowance made for that heat by using longer runways. This gives a longer run along the ground to accelerate to the speed that will allow the aircraft to fly. Once airborne one expects the climb performance to be sluggish so it is a good idea not to climb directly towards rapidly rising ground!

Load the aircraft up to its MTOM (Maximum Take Off Mass) and logically one will deduce that the heavier it is the slower the acceleration and climb performance will be. Deduction correct. All this is calculated before the flight takes place to ensure that a take off can be made safely and also legally.

One last thing. A twin engine piston aircraft has two vital speeds. Minimum control speed, below which the pilot will be unable to maintain control of the aircraft, identified on the airspeed indicator as ‘red line’ ; and Vyse, the best rate of climb speed on one engine, also known as ‘blue line’ speed. This speed should be the one to aim for in the event of losing an engine on take off once airborne. Slower than this will result in loss of performance.

Before take off we carry out ‘power checks’ to ensure that, as far as we are able to, the engines will develop full power after we line up on the runway and advance the throttles to fully open.

And so I did. All indications normal, with the oil pressure a little lower than at home in the cooler climate of the UK , but acceptable.
Temperature had been given as 47C so a tad warm outside and like sitting in a baked bean tin inside the cockpit with the sun burning down.

“Clear take off runway 35, wind direction 010degrees, 7 knots”

I lined the nose of the aeroplane up on the centreline and stopped, applied toe brakes and then set power for take off, a jolly juggle of 6 levers. Releasing the brakes the aircraft started to lumber down the runway. Poor old girl was at MTOM today and I expected performance to be lethargic.

Right hand seat safety pilot calling the speeds, the transition from airspeed alive to 85 knots took a while. All indications around normal. I gently eased the control wheel back to coax her off the ground. Poor aircraft really doesn’t like these baking outside air temperatures. Eyes outside now, dabbing the brakes just before selecting gear up, maintaining the centreline, waiting for the call from the other seat telling me I had reached blue line speed…..yet I knew I hadn’t. The aeroplane was talking to me through the controls. Something wasn’t quite right.

Glancing inside, the airspeed still read about 90 knots, well shy of blue line speed. Look back out, back in again, eyes this time on the vital gauges displaying oil temps & pressures. Left hand was a little lower than usual. Look back out the window, remember above all else to fly the aeroplane.
I was holding a little more right rudder than I should be in order to track straight. How much of that 4000m runway do I have left? I must be no higher than 100′. Not enough to get it down safely without running off the end.

Glance inside. Bugger! Manifold pressure on left engine dropping, apply full power on both, correcting for the yaw as the right engine gave me far more power than the left. Glancing out to maintain situational awareness and back in to each instrument in turn. Oil pressure needle now pointing at the red. The red at the low end of the scale. Damn.

Right, fly the aeroplane. Still getting some power from the left hand engine. With a rate of climb just registering and a maximum of 100′ a minute I am not denying myself the little extra power that the left is giving me at the moment. Alternate air? Tried. Mixtures? Fiddled with. Fuel? On and not the problem, have the correct fuel pressure and flow, leave them on these tanks.

That ground is very close. The engineer in the back has noticed it’s rather lower than usual. I retract take off flap, trying to minimise every bit of drag on the airframe. Lowering the nose a little more to maintain airspeed has us in level flight. Retracting cowl flaps to remove the last bit of drag I finally reach the blue line speed. The aircraft gently rises upward giving me a couple of hundred feet a minute climb rate.

Working under commercial pressure as we do, my mind briefly flirts with the idea of giving the task a go. A stupid idea that is discarded immediately. Press-on-itis has killed too many pilots and crew.

In the training environment a practice engine failure always assumes catastrophic failure requiring shut down of the engine in question. In the real world one often has some power available and if that power is enough it would be daft to shut the engine down. I have about 55% available to me so I’m keeping it.

Radio call made to Tower informing them of our intentions to land back as soon as possible, I concentrate now on securing the cabin and ensuring the other three persons on board are aware of the situation and that they are in no danger. We shall not however be carrying out a missed approach, so I need to land from this approach. With 4 km of tarmac in front of me that shouldn’t be difficult.

As I write this the cause is as yet unknown despite many hours diagnosis on the apron. Sadly had to eventually leave the aeroplane on the apron and leave on an airliner, whilst a solution is found. Whatever that solution, it is bound to be time consuming and expensive in a country where bureaucracy is rife and the pace of anything is excruciatingly slow. There are better countries to have technical problems it has to be said.


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