Hi Bob,

The example on page 4.3 has me a bit confused.

We calculate the ETP based on single engine figures but use an ETI based on two engine cruise.

If ETP figures are different for single engine and two engine, wouldn't using two engine to calculate the ETI be incorrect where the ETP has been calcualted using single engine?

Do explain.

Thank you.

The two calculations are quite separate.

Firstly you are calculating the point enroute where it will take the same time to go on or come home after an engine failure. That's the ETP based on single engine operation.

Now that you know where that point is, you are interested in calculating when you should reach that point on the planned trip. You will not be flying out to the single engine ETP on one engine. You will be flying out at normal operation.

Bob

Thanks Bob.
So will the ETP for a multi engine aircraft always be calculated on a single engine assuming one engine failed?
When would I calculate the ETI based on two engine as opposed to single engine?

Not always. It depends on the situation. For a multi engine aircraft you could calculate an ETP for single engine operation to cover the possibility of an engine failing, that's one possibility.

However you could also calculate an ETP for normal operation to cover an emergency other than an engine failure such as an electrical fire contaminating the cockpit atmosphere or a passenger having a serious medical problem etc.

Of course there would be many occasions where you would not need to do any ETP calculation, for example when there are lots of alternate aerodromes available along the route - say coastal from Brisbane to Cairns.

By the way, there will be no single engine ETPs in the CASA CPL exam because multi engine performance is not in the syllabus so the examiner cannot ask questions like that. I included it in the CPL Performance book because it seemed a pity not to at least mention it to up-and-coming CPL pilots.

Bob

Thank you Bob. That helped me out.