Vef etc

[AQVILA]

Hi everyone, im doin my ATPL'S and am yet again forced to look elsewhere othe than my course for better explanations.

Can someone give a clear thorough explanation of Vef, its relation to V1, and a clear definition of Vmcg.

I know its the speed at which the critical engine assumed to fail (?), but what in reality does that mean and why/how does it change if it does?

Any help much appreciated.

[Dick Whittingham]

When the calculations are done for finding V1 it is assumed that it takes 2 seconds to recognise an engine failure. Your stop/go decision can't be taken until you are sure what has happened so your continued acceleration is calculated as from the time at Vef plus 2sec for the "go" case.

In the "stop" case you have more to do - close throttles, select reverse get on the brakes - so there is a further 2sec put in before applying your stop data.


VMcg is defined as the minimum CAS in the take-off run at which, on failure of the critical engine with the remaining engine(s) at maximum available take-off power the pilot can retain control of the aircraft using primary aerodynamic controls alone. Use of the nosewheel steering is not allowed in the certification process and the trim must be set to the recommended take-off setting. The maximum lateral deviation from the centreline (assuming that is where the aircraft starts off) must not exceed 30ft (9.144m), from the point of engine failure until the aircraft is fully under control. No account is taken of crosswind which may, in reality, exacerbate the problem.

Now the apology - this is not my specialist subject and you will probably get much more relevant info from the experts

Dick