Hi
AeroTech,
You've asked two very good questions -
a)For takeoff and approach, there is an assumption of one engine failure regarding the climb gradient. Why not such assumption on landing (3.2% with all engine operating)?
There is such an assumption on landing. The 3.2% gradient which you've quoted is with (i) All engines at TOGA thrust, (ii) Gear DOWN, and (iii) Flaps at the landing setting. Approach Climb Gradient must be provided for, and AFM data provides for a 2.1% Gradient with (i) One Engine operative, the remainder at TOGA thrust, (ii) Gear UP, and (iii) Flaps at the Approach Climb setting. (Flaps at the Approach Climb setting are typically at or close to normal Takeoff Flap settings). There is no lower altitude limit where Approach Climb (i.e. Engine Inop) may be used, it would also apply at the DH for a Cat III landing.
PANS-OPS and TERPS provide for a minimum 2.5% Gradient during missed approach, providing 100 ft of Obstacle Clearance. It is up to you, the pilot to compensate for the 0.4% difference between AFM Approach Climb "guarantees" and the required 2.5%. (You may use either of an increased approach minima, or consult performance data to guarantee 2.5% OEI Climb Gradient, or greater if required for the location).
b)How a takeoff thrust time limit (5/10 minutes) can affect the aircraft (take off climb gradient, takeoff path,…)? Does this occur in reality (a fact and not only a theory) only during takeoff or even during go-around (missed approach, engine failure)?
Very much so, particularly for the 5 minute limited aircraft. An actual example is probably the best explanation. I was working OEI Escape Routes and obstacle data for an Australian airport with numerous obstacles in the 2nd segment climb, and a "further out" higher obstacle in the 3rd Segment. The obstacles in the 2nd Segment required a somewhat increased OEI gradient, but still provided quite useful and commercially viable RTOWs for the Runway. So far, so good.....
Although the "further out" obstacle actually subtended a quite modest gradient to the runway, and thus didn't affect 2nd Segment, it
DID require 3rd Segment MAA to be increased to 1650 ft AFL. Your every day 2 engined aircraft can usually handle MAA of 1100 to 1200 ft within the 5 minute limit for Takeoff Roll, 1st Segment, 2nd Segment, and 3rd Segment acceleration to Clean configuration within 5 minutes. The (actual case) 1650 ft MAA required well in excess of 5 minutes at Takeoff thrust to reach Clean configuration. The only solution was to ARTIFICIALLY "bump up" the 2nd Segment climb gradient to somewhat more than required, in order to achieve MAA in a shorter time, and constrain the time to Vcl within 5 minutes. Thus, 2nd Segment weight limits for the higher gradient significantly reduced the RTOW for the runway, reducing these to marginally commercially viable. (A 10 minute limited aircraft would have had no problem).
So...... The time limit at Takeoff thrust can directly impact upon Limiting Takeoff Weights.
Regards,
Old Smokey