1st/2nd Segment Obstacle Correction Factor
To the performance gurus. I'd like some help in QAing the following procedure:
Our ops manual has a procedure to correct the published TODA/STODA to guarantee that both 1st and 2nd Segments are able to be conducted clear of obstacles. This is due to the reasoning that when using ERSA STODAs, the height and horizontal distance for the limiting obstacle(s) is unknown and the first stage may be compromised.
The fix is to reduce the STODA by a given margin, thereby supposedly containing the 1st stage within the runway strip e.g. If using a 5% STODA, 60m is subtracted, reducing down to a 1.6% STODA correction of 20m. This then gives a corrected TODA, which is used for calculating runway and climb limitations.
Issues:
1. If operating at a non-obstacle limited airfield, the corrected TODA could be longer than the actual true TORA e.g. subtracting 20m on a 1.6% slope would still put the TODA in the clearway (We only calculate a balanced field V1)
Fix: Need to use the lessor of ASDA, TORA or corrected TODA.
2. If they're worried about 1st stage protection, then 60m (197ft) seems a bit small. A max V2 of 150kts (253fps) means that the "buffer" is gone in less than a second, and the aircraft will not be climbing at the 2nd stage gradient when it starts to impinge outside the clearway.
Fix: Better gear retraction time (therefore distance) data?
We don't use this often as most of our ops are covered by RTOW charts.
Does anyone else use a similar procedure, or do you simply accept the fact that the first stage does not actually impose upon published gradients, and only consider 2nd stage performance (or use what ever the ops section gives you?)?
Anyone like to add constructive criticism?
Last edited by Ex Douglas Driver; 2nd May 2006 at 01:36.
Reason: Edits in Itallics to correct errors