View Full Version : Take-Off Performance 2 engines?

8th Mar 2008, 01:22
Could somebody please explain the 4 segment climb for a 2 engine aircraft. I have been through the regs. but I am not sure where the first and second segment starts and where they end and what are the climb gradients required.

2. Where does the screen height of 35 ft come into the climb segment.

3. What is the a/c configuration in the segments.

4. At what point is V2 reached.

8th Mar 2008, 03:23
Good evening. The segments for certification apply to all current transport category aircraft, 2 engines or more.

I'll use a dry runway reference:

Reference zero is 35 feet, gear down.
First segment starts at Reference zero, ends when the gear is retracted.
Second segment is flown at V2, gear up, flaps in takeoff configuration and ends at the acceleration height.
Third segment is flap retraction, conducted normally at takeoff thrust and ends when the aircraft is clean and at max continuous thrust.
Final, or fourth segment is enroute climb, clean and at enroute climb speed, single engine.

Does this fit the bill?


Old Smokey
8th Mar 2008, 15:06
Vsplat, welcome aboard, a nice effort for your first post. May there be many more of similar calibre!:ok:

As arrow28 did ask "what are the climb gradients required?" -

1st Segment : Positive climb gradient (Not as bad as it sounds),

2nd Segment : Minimum 2.4% Gross degraded by 0.8% to 1.6% Net, or more as required for obstacle clearance,

3rd Segment : Level, but the aircraft must have the climb gradient capability of 1.2% throughout the level acceleration,

4th Segment : 1.2%

The requirement for a mere "positive" climb gradient for the 1st segment is NOT as bad as it sounds, typical deltas between 1st and 2nd segments are usually of the order of 1.0% or less, thus, as the aircraft MUST achieve at least 2.4% Gross during the 2nd segment, Gross gradient in the 1st segment would be in the 1.4% "ball-park". Again, not too bad, as no credit is allowed for ground effect in the 1st segment during certification, a further plus.


Old Smokey

8th Mar 2008, 17:22
Thanks, I missed the question on required gradients entirely. That's what I get for leaving my bifocals upstairs....

On the topic of required gradient by segment, something to add here is that there are really two aspects to these gradients. One is basic WAT certification, (the gross percents indicated) which, as OS indicates, do not reference ground effect, but also don't reference obstacles. The second requirement is to degrade the gross climb performance before using it in obstacle clearance calculations (net takeoff flight path).

When a student asks me what the required climb gradient is for an operational exercise, I normally respond first with 'whatever it takes to miss the rock'. The net-to gross decremenents vary with the number of engines, OS provided the data for a twin. Depending on the obstacle analysis method used, there may be other additives. 35 feet is standard, however when departing from a wet or contaminated runway, there are tricks played with this. If a turn is involved, the margin generally is increased.

When providing min altitudes for turns or acceleration, operators are required to identify the gross altitude (i.e. what the crew will see on the altimeter) for the maneuver. Depending where in the world this is done, there may be yet further additives for altimeter error and cold temperatures. On occasion these themselves can back-drive an increased climb requirement and associated weight decrement.

I see a related question on climb gradients on all engines on another thread. I'll wander over there shortly. There is a common belief that analysing a departure for the one engine inoperative case guarantees SID climb gradient compliance. Not actually true.

I've probably gone from too little all the way over to too much, now that I'm armed with my glasses AND too many coffees....

I should ask what region you are considering. Beyond the basic stuff discussed here, there are differences between ICAO, Europe, US and Canada.


Pugilistic Animus
19th Mar 2008, 20:09
Although this was not asked it is a related issue---

the minimum speed that must be achieved for the third segment is 1.25 Vs [US FAR 25]

so minimum acceleration is from V2---1.25Vs...with the required gradient specified by Old Smokey---He could write a 5000 page textbook titled 'Airplane Performance'

Vsplat, "here is a common belief that analyzing a departure for the one engine inoperative case guarantees SID climb gradient compliance. Not actually true" ----

--- In the US what you said is so true because the departure tracks may differ because unlike some countries; in the US OEI performance is not considered in the departure track all engines is assumed--but as you stated every country does TO Perf differently:\