Re: Power for Take-Off

Date:         11 Sep 97 03:35:31 
Organization: University of Nevada System Computing Services
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Chris Dahler ( wrote:
: All multiengine aircraft, from light piston twins to the B-747, have to
: be able to accelerate to takeoff speed, lose an engine, and still be
: able to meet certain climb criteria before the FAA will certify the
: aircraft as airworthy.  <snip>

Not quite.  It's true that FAR 25 aircraft must meet minimum one-engine
out climb criteria in order to be certified.  However, "light piston
twins" are certified under FAR 23 which has no such requirement.  In hot
and high conditions (such as here in Las Vegas, NV) it is quite common to
takeoff in a light twin that WILL NOT FLY if one engine decides to take
the rest of the day off.  So the mental drill that the pilot of a light
twin goes through at the beginning of the takeoff run is a bit different
then that of a FAR 25 aircraft driver.  The usual takeoff sequence for a
light twin is something like this:

1. Have a look at the single-engine climb performance chart.  If it indicates
   negative rate of climb for your conditions, you may wish to reconsider
   the need for this takeoff.  If you do decide to go, you accept that
   you are BETTING THE AIRCRAFT (and its contents) that both engines will
   run at least to a point where you can comfortably deal with an engine
   failure (usually 500'AGL).  Do you feel lucky?
2. Establish and CHECK power very early in the takeoff roll (or even set
   power with brakes set, then release.)  If power fails before rotation,
3. After rotation, accelerate to Vyse (best single engine climb speed).
   Leave gear down.  If power fails here (below Vyse), ABORT back onto the
   runway.  Most light twins will not fly (let alone climb) in this
   configuration at typical takeoff gross weight unless at or near sea level.
   The old saw here is it's better to go through the fence at 50 than into
   the trees at 100.
4. Above Vyse and when there is no usable runway left, raise the gear.  If
   you lose one here--and quickly/correctly do the ol' identifyverifyfeather
   routine--you are in the configuration that produces the best climb on
   one engine (or in many cases minimizes the sink rate).  The aircraft may
   indeed continue to sink in this configuration--FAR 23 does not guarantee
   single-engine climb capability!  The pilot's only choice here might well
   be to find a nice soft spot off the end of the runway to stuff the
   airplane into.
5. Climb through 500'AGL.  Losing one here means you might just make
   it through either a 180 degree turn to set up for a downwind landing OR
   make it around the traffic pattern for a single-engine approach and
   landing--assuming your technique is up to the task.

The single-engine service ceiling in the typical light twin is generally
lower than typical cruising altitudes.  So...if you lose one in cruise
you will drift down to whatever the single-engine service ceiling is that
day.  If the ground is higher than that (not at all unusual out here), then
it looks like you're going to land--at an airport if you did your flight
planning, otherwise...

Another old saw about light twins is:  The other engine just helps you
get to the crash site.  Fly safe out there!


Paul Mayer  UNLV, Las Vegas, NV
ATP, AGI, IGI; former YR F/O (DHC-6-300) and now
Just a Japanese 221 student at UNLV.
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