Turn as soon as practicable 2

21.10.2005

Submission:

For a turning departure procedure or missed approach procedure (MAP), is there any altitude requirement for aircraft to commence the turn? According to the airline operator, they have a requirement of 400 feet before their aircraft can initiate a turn. If a MAP that requires the aircraft to turn as soon as possible, should I consider this 400 feet in the design?

GC Hong Kong procedure specialist

Answer or Commentary:

(I.W
As far as I know, for a departure Pans-Ops states a minimum altitude of 120m (394 ft) before an aircraft will make a turn. This basically equates to area 1 where the early turn and the straight ahead portion are both covered

Now to the missed approach case.

Firstly if the operators say that they will climb to 400 ft before making a turn, I would personally, take this fact into account when designing the procedure. However I would not put that fact on the chart but just leave it as "turn as soon as practicable".
Pans-Ops states:

Where the turn is specified at the MAPt, which means that the pilot is supposed to establish the aeroplane on a climbing path and, then to turn, the OCA/H will be taken as the turn altitude/height and the turn initiation area will extend from the earliest MAPt to the SOC.

This seems to suggest that ICAO expects an aircraft to turn at the start of climb (SOC) not 400 ft above it. However Pans-Ops also give an aircraft on a non-precision approach 18 seconds from the latest tolerance of the MAPt to the start of climb (SOC). I heard that the reason why it is so long (transitional tolerance 15 sec) is because it took the DC8 or 9 that long to retract the flaps and gear so it could start to climb. So I personally think that in reality modern aircraft will be 400 ft at the start of climb (SOC).

In the ILS case, I think that the only way one can analyse a "turn as soon as practicable" is to use the green pages attachment J to part III and make the turning altitude the OCH. In this case you get more altitude if the aircraft climbs to 400 ft (better case). However if the "turn as soon as practicable" is due to obstacles straight ahead and not just for parallel operations there is a problem. With obstacles straight ahead in the missed approach I would personally evaluate them with the 400 ft included but evaluate obstacles in the turn area using the OAS altitude contour of the OCH.

Have any of the other procedure designers evaluated "turn as soon as practicable" procedures and what criteria did you use?)