Probability of Two Engines Failing

Date:         06 Aug 98 11:26:15 
From:         ranfaa@my-dejanews.com
Organization: Deja News - The Leader in Internet Discussion
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When the big twins first started transatlantic operation this was the formula
that the mathematicians produced to predict the first twin ditching through
multiple engine failure.(The original date I don't recall) Needless to say
that time passed a long time ago.

The probability of a double power unit shutdown from independent causes is
expressed as (2 P1 P2 T Y )where P1 is the probability of a single engine
failure in cruise per hour,  P2 is the probibility of second engine failure, T
is the flight time duration, and Y is the diversion time at single engine
cruise speed to the nearest suitable aerodrome.

P1 is conservatively assessed by the ICAO study group as the recorded
shut-down rate fo the mature aircraft -engine combination.

P2 the probability of second engine failure from an independent cause, will
be higher than P1 because the second engine will be operating at higher
power; sot the study group recommends that P2 is 2P1.

A double engine shutdown is regarded by most airworthiness authorities , and
by the ICAO study group, as 'catastrophic" in other words , fatal. Allowing
for he probability of a fatal crash resulting from total engine failure from
independent causes to be one in 100 million hours , or 10 to power of -8, the
study group recommends the folowing formula for assessing the required
inflight shutdown rate for a particular route:

10 to power of -8 (0.6 + 0.4 T ) all divided by T Y

The question we asked in QANTAS was:

WHAT IF THE SECOND ENGINE FAILED FIRST ?

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