gunshy67
3rd Jan 2008, 02:52
In Australia years ago the end of the net /gross takeoff profile finished at 1,500' above the airfield height/altitude.
This has been changed some time ago to a requirement to ensure the take-off profile can clear all obstacles to Lowest Safe . But Lowest Safe has generally a 1000 ft miss requirement to obsatacles within 25 nms - whereas all the profile requires to the 1,500' is 35 feet for straight out or 50 feet for the curve. Why is this 35' miss requirement not so for the LSALT? What am I missing?
Old Smokey
3rd Jan 2008, 11:26
"What am I missing?"............The obstacles, hopefully.
What you say is true, the Australian requirements do indeed require obstacle clearance up to the MSA, but you have to do a bit of cross reading between CAO20.7.1B and the AIP to get the full picture (For furriners, CAO20.7.1B = FAR 25).
The Obstacle clear climb does terminate at the MSA, but the actual obstacle clearance offered by the Net profile remains at 35 ft (or 50 ft if turning). For example, if a 1000 ft obstacle existed within the MSA coverage, creating a MSA of 2000 feet, the Net clearance of the critical obstacle would be achieved at 1035 ft, but climb must continue to 2000 feet. Upon reaching 2000 feet, CAO20.7.1B terminates, and PANS-OPS requirements prevail thereafter.
In practice, it's not as serious as it sounds, if good routing for the EOSID is chosen, it's possible to LATERALLY clear the worst of the obstacles with required climb gradients and Minimum Acceleration Altitudes at much less than the elevation of the most critical obstacle 'creating' the MSA. Good EOSID routing can then position the aircraft in an area for further climb to MSA whilst laterally clear of the worst of the obstacles.
That's the way I do it, others may differ.
Funny timing for your post, only today one of the 'chiefs' asked if some of the EOSIDs could be simplified. I replied that they could, if his budget was large enough to purchase a few megatons of TNT for obstacle clearance.:ok:
Regards,
Old Smokey