The topic has come into the news here of the possibility of takeoffs at
Sky Harbor being suspended this weekend due to the forecast high temperatures.
This happened back in 1990, and the news people stated that it was because the
takeoff data charts did not go high enough in temperature. Actually, that's
just part of the real story.
In multi-engine aircraft, there are terms like "refusal speed", "critical
engine failure speed", and "critical field length". It's this last one that
comes into play here.
Refusal speed (Vr) is the maximum allowable speed that can be attained
with normal acceleration, from which a stop may be completed within the
available runway length
(http://www.flashcardmachine.com/told-definitions1.html).
Critical engine failure speed is defined as the speed at which one engine
can fail and the same distance is required to either continue to accelerate to
lift-off speed, or abort and decelerate to a full stop.
Critical field length is the total length of the runway required to
accelerate on all engines to critical engine failure speed, experience an
engine failure, then continue to lift-off or stop.
Now comes the fun part. Category 1 is the situation where the available
runway is greater than the critical field length, which is typical. Category 2
is where the available runway and the critical field length are the same.
Category 3 is where the available runway is less than the critical field
length. You are not allowed to takeoff in category 3 situations. Period.
Back in 1990 most airlines operating out of Sky Harbor were using the
fairly new 737-400. Now we have the 737=800 as well as other comparable
aircraft. It remains to be seen how our extreme tempratures this weekend will
affect operations.
Chris
When the going gets weird, the weird turn pro
- Hunter S. Thompson
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