Thank you!

I guess 400' comes from those being the minimum OCH in the aerodrome area within a radius of X miles.
Don't have a copy of ICAO Doc.8168 right at hand, could anyone check that out?

JM2PW...

cheers!

3.3 % climb gradient,394 feet & 15 degree turn !

does it ring a bell ? :O

Many of you would gain from the history of ICAO documents
 

One of the wonderful things that came about as a result of the ICAO Convention of 1944 was the consultative groups that were formed to develop the Standards and Recommended Practices for world aviation as empowered under Article 37 of the Convention. Those consultative groups not only thrashed out rules within their own areas of expertise but also ensured that the world was provided with one of the most cohesive and consistent set of guidelines for everything aviation.

400 feet appears in many of the ICAO Annexes - it is a standard level for obstruction charting, aircraft performance, instrument approach design, obstacle limitation surfaces for aerodromes, etc. There would have been many inputs into the original derivation of the 400 ft from all of those areas and undoubtedly many conflicting imperatives. I have no access to the historical data that would record whether the FAA adopted the ICAO figures or vice versa, but suffice it to say that 400 ft is a universal standard for control of the design of aircraft and the associated infrastructure.

ICAO is as much about an economic level playing field as it is about safety - lowering the minimum acceleration height would change to power requirements for aircraft (less), perhaps reducing other related performance requirements while substantially increasing the costs of rewriting all the AFMs, conducting airport surveys, making charts, installing obstruction lighting, maintaining obstacle control, limiting noise pollution and other environmental consequences, etc. And of course, each Contracting State would need to ratify and codefy the changes to an agreed schedule and....

I for one do not want less installed power or engines with shorter power ratings limits nor do I want to accelerate closer to the terrain than what is already a litle daunting if you watch the oibstacles coming at 1.6%.

We seem to use 600 feet on the airports we fly to(Boeing 727). Isn't it true that lowering the acceleration height increases the payload capability?

The 400ft above the runway and the 1500ft above the runway are as was said earlier simply markers to set performance values against.

They are specified in the certification requirements of FAR -23 and FAR - 25 as well as CS-23 and CS-25.

They ensure that certain standards are met.

For example a CS-25 twin engine aircraft must have a certain minimum climb gradient in the second segment. 400ft is simply the minimum height that the second segment can end at.

That prevents some manufacturer from trying to certify an aircraft that they claim has a second segment climb gradient of the minimum required but only up to 200ft!!!!!

Just like the balked landing minimum climb gardient requirement these are simply certification requirements.

Since the 400ft above the runway is a certification requirement there is no relationship to obstacle clearance which is a totally separate issue.

Edit to say that what is also tied in with the 400ft lowest end of the second segment is the 5 minute take-off power limit (10 minutes on some aircraft).

Without this 400ft yardstick, some designer could claim that an aircraft which could only manage the minimum climb gradient to 100ft and which had to level at 50ft in order to accelerate to min clean within the time limit when at max weight should be put into production!!

Regards,

DFC