Originally Posted by
PantLoad
As usual, Old Smokey provides and excellent explanation of the issue at hand. Thank you.
This thread is related to another that is currently running about the use of Flaps 2 on the 737. It is important to note that airplane manufacturers have takeoff performance figures for several different flap settings. For example, Flaps 2 on the 737 is approved for some models. It is the option of specific operators regarding what data are to be provided to the line pilots.
I remember years ago, my company provided Flaps 2 performance data for Flaps 2 (on our 737-200) for certain airports, in addition to Flaps 1 and Flaps 5 data. Generally (and the key word is 'generally'), Flaps 2 provided a nice balance between takeoff run and second segment climb performance (Flaps 1 vis'-a-vis' Flaps 5).
My old company (I've been retired for several years, now.) published in the Pilots Operating Handbook (POH) the statement that "Flaps 5 [was] the preferred flap setting for takeoff". Unfortunately, many of my fellow pilots took this to mean that Flaps 5 was the ONLY flap setting to be used, unless conditions (weight, runway length, density altitude, etc.) mandated a lesser takeoff flap setting.
In one specific situation, we were taking off from a sea level airport on a hot July day (OAT maybe 35c)...relatively heavy weight...but we had well over 10,000 feet of runway. We were legal and safe for either a Flaps 1 or a Flaps 5 takeoff. I can't remember the specific numbers, but here are the approximate figures:
Actual takeoff weight: 127,500 lbs
Max weights for Flaps 1 and Flaps 5: (In this particular case, we had no Flaps 2 data.)
Runway Limit - Climb Limit
-----------------------------------------------------------------------
Flaps 1 - 128,500 - 128,700
Flaps 5 - 129,200 - 127,800
As you can see, Flaps 5 provided a much better safety factor in the event of an RTO, but an engine failure at V1 (continuing the takeoff on one engine) would have been 'tight' as we were only 300 lbs below the max for second-segment climb.
Conversely, Flaps 1, while generating higher speeds...and making an RTO at V1 minus 1 'interesting' (thus soiling underpants)...provided a better overall safety factor (in the event of either an RTO of continued climbout OEI).
We had published speeds along with the above data (We received all this over ACARS around pushback time.), and the V1 speed for Flaps 1 was about four knots higher than the V1 speed for Flaps 5.
Tire and brake energy speeds were respected in either case...as either flap setting was legal.
I discussed this issue of takeoff flap selection with the first officer, and he insisted that we HAD to use Flaps 5...to be in compliance with the POH doctrine. My point of view was that we had a better safety cushion if we used Flaps 1.
I believe the F/O's confusion existed because some of the captains with whom he had previously flown didn't, themselves, understand basic performance...and the fact that he didn't properly interpret the POH statement.
We took off with Flaps 1...being legal and safe and in compliance with our company's SOP...but not without heated objection from the F/O.
The moral of the story is that we should consider all factors when choosing takeoff flap settings....and look to the manufacturer's published performance figures (as supplied by your company) as a guide in this decision process.
Another factor to consider, by the way, is runway surface condition. If it's rough...to where you really need four-wheel drive for your takeoff run..you might lean towards a higher flap setting...all other factors being approximately equal.
Fly safe,
PantLoad