Mixture cuts to simulate engine failure on take off.
In Australia it seems that many flying instructors on multi-engine aircraft cut the mixture control to simulate engine failure shortly after take off.
The reasoning is that it gives the student a harder job of identification because both throttles are wide open for take off - whereas a throttle closure to simulate failure makes it more obvious which engine has failed.
I understand that in UK, simulating engine failure after takeoff by mixture cut is frowned upon by the UK CAA because of the risk of mis-handling?
The engine manufacturer Lycoming state that a mixture cut is kinder to the engine due to a cushioning by air pressure of the pistons - providing the throttle is open.
But the offending throttle is normally pulled back fairly early in the identification process which rather negates the aim of the Lycoming advice which applies to full throttle. Lycoming add that despite the good engine handling that applies to a mixture cut, they advise it is "safer" to not use the mixture cut as a means of simulating engine stoppage, but to use the throttle as it has the advantage of being able to reintroduce instant power if a stuff up occurs. The US NTSB concur.
Nevertheless, experience has shown that flying schools around Australia still prefer to use the mixture cut to simulate engine failure after takeoff in a twin. Australian CASA apparently takes no position on the subject judging by their lack of interest.
Now comes the interesting bit. I wonder how many instructors use the mixture cut on a single engine aircraft to simulate engine failure after takeoff - rather than close the throttle? Well, why not? After all, it is "good" for the engine - according to Textron Lycoming.
Having said, that it is a good bet that no instructors in their right mind would cut the mixture to simulate an engine failure on a single engine aircraft at 500 ft agl after take off. And if asked why they would not use the mixture, they may give several good reasons including:
The engine may not start again.
The mixture cable might break.
Not enough time to save the situation if something drastic happens.
- and the aircraft would be up the creek without a paddle, wouldn't it?
If you agree so far that a mixture cut in a single would be potentially dangerous - then why would should a mixture cut be any less dangerous on take off in a twin?
After all, if the engine wouldn't start when the instructor tried to set up zero thrust, then in very quick time there will be a rapid speed bleed off with a windmilling no power propeller. And we all know that light twins have a lousy rate of climb with one feathered let alone with one windmilling.
And if the possibility of a mixture cable breaking in a single is a good reason for only doing a throttle cut when simulating engine failure after take off - then surely the same principle applies to a mixture cut in a twin on take off. After all, it will be the same result - which is a dead engine and a windmilling prop and down goes the aircraft. Unless feathering action is taken by the instructor real quickly after he realises that the engine won't start with a busted mixture cable. And you can just imagine the hands flying in all directions if that happens with the student wondering what the hell is happening. A recipe for utter confusion!
Would you agree therefore, that mixture cuts after take off in a twin in order to simulate engine failure - is poor risk management, compared to that of using the throttle to simulate failure. What's good for the single engine aircraft in this case surely holds good for a twin.
Think it over carefully and imagine the lawyers having your guts for garters if you killed someone while cutting the mixture after take off during training.