Calculating Drift down after Engine failure

[Old Smokey]

Contained in AFM data?.............Not always, but the information required to make the computation of the Drift-Down profile is contained in the AFM.

ARINC, As you posed that it was an acedemic question in discovering how drift downs are calculated after engine failures, here's the procedure that I use for calculating the Time / Distance / Fuel / Altitude profile for "less civilised" aircraft that do not provide the resultant profile in the AFM -

The AFM should provide -

(1) The One Engine Inoperative (OEI) speed schedule to be flown following engine failure, and
(2) the OEI Gross/Net climb gradients for the complete range of Weights, Pressure Heights, and Temperatures, and
(3) the Referred Fuel Flow for the remaining engine/s at MCT.

For a given Start weight, En-Route Pressure Height, and Temperature deviation from ISA, extract the OEI gradient, TAS, and Fuel Flow.

.1. For a very small increment of fuel (I do it 1 Kg at a time), calculate the time taken to consume the fuel increment at the MCT Fuel Flow,
.2. Apply the gradient to the TAS to compute the horizontal distance flown, and height lost (or gained) for the incremental time to consume the fuel,
.3. For the new height, and new gross weight after consuming the incremental fuel, return to step .1. keeping a running total of Time, Distance, and Fuel, until the gradient has reached zero. Drift-Down has ended when the gradient is zero, but the process may be continued to ascertain continued En-Route Climb as fuel continues to burn off.

Such a procedure as described above will obviously involve literally thousands of 'cycles' between step 1 and step 3, and is only really suitable for a computer programme unless you have a lot of time on your hands. From several computer runs at a series of Starting Weights, Temperatures and Flight Levels, a series of Drift-Down tables may be produced for the AOM.

With respect to the journalistic 'Himalayan death plunge' alluded to in earlier posts, it is quite typical, at normal cruise levels, weights, and temperatures to see a Drift-Down which may take up to one and a half hours to complete. Even, immediately following engine failure at cruise speed and setting MCT, it can take up to 5 or 6 minutes of level flight before the speed has reduced to Drift-Down speed, and Drift-Down commences. Sorry journos, you'd better go looking for a 'death plunge' somewhere else.

PS - The D.D. table is coming Rich, it's coming, work is the curse of the Pruning classes.

Regards,

Old Smokey