View Full Version : Question for John Tullamarine and Old Smokey

Bruce Waddington
26th Jan 2010, 06:37
John, Old Smokey,

Standard Obstacle Clearance runs a slope upwards from a point 35 feet above the end of the departure runway at 152 feet per nautical mile to check for obstacles.

My questions, after searching TERPS and PANS OPS, are these;

1. How far does this evaluation go out ?

2. Why do some manufacturers choose 400 above airport elevation (or clear of obstacles if higher) to enter the third (transitional) segment and some manufacturers choose 1500 above airport elevation (or clear of obstacles if higher) to do the same ?

Many thanks in advance,

Bruce Waddington

26th Jan 2010, 10:57
My ops eng work has been pretty well exclusively to Oz rules so I'll leave the first question to OS and Mutt who play in other jurisdictions.

400ft is the minimum third segment under the normal airworthiness design rules (I can't open the FAA site just now to cite the FAA rule but one of us will, no doubt, do so in due course) so the usual flight manual data has this as the lowest data level for analysis.

Normally the takeoff is taken to have been completed at 1500ft so the usual AFM data presentation will provide for 400ft through to some level generally not exceeding 1500ft. There is no reason why an OEM can't use a higher level if that is considered to offer a marketing or similar advantage for a particular Type.

Sometimes a system limitation will truncate that range eg RR Dart aircraft usually are limited to 600ft due to an autofeather pump limitation as I recall.

26th Jan 2010, 13:20
400' is a carry over from the water injected days. It would allow for acceleration and clean up before you ran out of water. I looked for that piece of information for a long time.

27th Jan 2010, 00:06
If I may,
TOCS takeoff climb surface(for each r/w) is the area beyond clearway, or if no clearway exists then a min 60m from r/w end upto15000m.
do correct me if i am wrong

galaxy flyer
27th Jan 2010, 01:41

IIRC, TERPS runs the evaluation out to where, in the case of diverse departure
(omnidirectional for PANS-OPS) the OCS intercepts the lowest compatible airway MEA or MIA (min instrument altitude). For SIDS, I am not sure but probably similar--an MEA. Note, it is the lowest airway MEA, so there might be a disconnect between the lowest and the airway you are departing on.

OEMs do perf charts differently, some go well beyond 1500' AFL, the one I am familiar with charts to 12,000 AFL including corrections to the V2 speeds when level-off is above 1500 feet.


27th Jan 2010, 01:56
Can't you get a higher payload if you use a lower third segment?

galaxy flyer
27th Jan 2010, 02:25
Not if the third segment is cumulo-granite. Higher level-off heights are for terrain clearance.


27th Jan 2010, 02:56
Many airports have departure procedures over flat terrain. I seem to remember that having a lower third segment can allow a higher takeoff weight at least in some cases.

Anyone care to confirm for me.

27th Jan 2010, 05:41
400 feet is a holdover from CAR4B...one cannot use lower due to certification rules.

27th Jan 2010, 06:35
Gentle people
Somewhere in the back of the old grey matter, I recall the longitudinal distance for OCS as being 7,500m. Unfortunately, I cannot find the specific reference.
However, in a recommendation to my company for a EOSID for PANC RWY32 because engine out considerations of third segment (1100ft QNH) which on a straight takeoff path puts aircraft through a major LAC (light aircraft lane (but that is another story), I came across CAAP (Civil Aviation Advisory Publication) 235-4(0), which apart from providing a great deal of information on EOSIDs, provides a great many references relating to engine out/performance critera. The URL is:

27th Jan 2010, 18:47
B.W the PANS OPS 4 further indicates that the acceleration segment criteria have been deleted, as formerly published in ICAO Document 8168, Volume II, First, Second and Third Editions. 1500 ft as a minimum acceleration hight seems to be a reasonable value covering all versions of PANS OPS. Just my 2 cents.:ok: