Performance limitations and operating procedures
If I may be permitted to add a few observations to the discussion:
A distinction needs to be made between limitations and procedures.
“The aircraft is (obviously) certified to takeoff, fly and land with gear down.”
That is a somewhat simplistic statement. The aircraft is certified for operation within the limitations stated in the Airplane Flight Manual (AFM). The AFM states that the weight that achieves the minimum climb gradients for altitude and temperature (WAT limit), and allows takeoff within the available lengths of runway, is an operating limitation.
In addition, there are usually operating rules, for example FAR parts 91 and 121. FAR 121 adds the requirement that the takeoff weight must permit a net flightpath that clears obstacles by the required margins.
Although most performance limitations are based on a scenario of engine failure, it is not correct to say that they are totally divorced from the performance in normal operation with all engines operating. That is perhaps somewhat beyond the scope of this forum, to understand it you have to go back to the origin in the Final Report of the SCOP that JT mentioned. Let’s just say that the certification basis assumes that the airplane will be operated by qualified pilots in accordance with the recommended procedures.
Note that all performance limitations are stated as a maximum allowable weight for the prevailing conditions. Exceeding any of those limitations is an offence against the law and may result in sanctions, irrespective of whether that exceedance is a factor in an investigation. However, any accident report that I know of, usually has a statement in one of the first sections to the effect that “the weight and loading were within limits”.
Then there are operating procedures. Operating procedures for performance are stated in the AFM in the form of ‘guidance material’, to enable the flight crew to achieve the performance assumed in the calculation of weight limitations. Deviating from those procedures is not a punishable offence, but may result in an invitation for a “tea and biscuits” with the chief pilot. If the deviation is a factor in an incident or accident, the pilot will be asked to explain why he considered it safe to deviate from the Standard Operating Procedure (SOP). If the investigation finds that explanation unsatisfactory, sanctions may follow.
Regarding flap retraction after takeoff from Cologne, my understanding is that such on operating restriction is usually complied with by maintaining a certain rate-of-climb. The acceleration remaining while maintaining that rate of climb will determine when you reach flap retraction speed. At that speed you can retract the flaps.
P.S.
Another way to put it: by delaying gear retraction, you’re reducing the performance margin that you may need in a contingency. In other words, you’re making the takeoff less safe than it could have been, unless you can show a safety benefit for delaying gear retraction.
Last edited by Gysbreght; 25th Jun 2015 at 18:49.
Reason: adding a P.S.