Acceleration Altitude 400ft AGL

[Speedwinner]

Hello!

In my company we do the cleanup with the 737-800 in 1500ft AGL normally. I was reading about the 400ft agl that some do it there. since you need 2,4% in this segment how can you accelerate at 400ft agl? Where does this magical number of 400ft come from? so is it right that we compensate the 1,2% in the third segment with the accelration since we climb to 1500ft? means the 1100ft are converted in the acceleration?

Thanks folks

[FE Hoppy]

The second segment climb requirement of 2.4% ends at acceleration height. The lowest this is allowed to be is 400ft. As soon as you begin accelerating you are in the 3rd segment.

[rudderrudderrat]

Hi Speedwinner,

There was a good discussion on this early this year. Search for "A320-engine-out-acceleration" and have a look at fredgrav's graph.

here (http://www.pprune.org/tech-log/413142-a320-engine-out-acceleration.html)

400 ft is the minimum AA we are allowed under the rules - it can be higher. (Most companies use a higher one).

[reynoldsno1]

400ft agl is also the lowest turn altitude for departures in PANS OPS ...

[EW73]

Also my memory tells me it's the lowest altitude you can engage either autopilot...

EW73

[eckhard]

Also my memory tells me it's the lowest altitude you can engage either autopilot...

I think that depends on the aircraft type. On the 747-400 the lowest AP engagement height after take-off is 250ft. On some aircraft I have flown it is 1000ft.

Acceleration Height is purely a performance issue; nothing to do with autopilots.

There may also be a lower height for turning than that specified in PANS-OPS (300ft in some cases I know of).

Some AFDS modes may not engage until 400ft (HDG, LNAV, VNAV), but again this is type specific and nothing to do with performance.

Some manufacturers specify an Accel Ht of 400ft and then publish NTOFP data to go with it. Some specify 1000ft, others 1500ft. Some even let you decide (subject to the minimum allowed by regulations of 400ft). The normal maximum is 1500ft but even this can be extended if required by terrain. Other factors may then come into play (e.g. 5 minute limit at TO thrust).

The choice of Accel Ht can be influenced by the distance from (and height above) reference zero of 'dominant' obstacles. A close-in obstacle may mean a higher Accel Ht is preferable, whereas a distant obstacle may make a low Accel Ht more efficient.

[Type1106]

It's really quite simple. 400' is the minimum height for the end of the 2nd segment - the 2nd segment can be extended to 1500' or any where in between once you are clear of the dominant obstacle (if any exists). The height is sometimes referred to as HA or height for acceleration and will be different for each airfield depending on obstacle - unless,of course your SOP uses the 1500' figure as standard.

Now, this is basic Schedule A Performance (remember that difficult exam you took, probably as part of your CPL never mind your ATPL) but many operators use 1500' for simplicity.

Also, remember this is about NET performance (i.e. making the required gradient in the 2nd segment) with an engine out. Your GROSS performance should be much better on the day. Incidentally, from the end of the 2nd segment it is assumed that you fly level to accelerate and flap retract: no turns are allowed for in the 3rd segment because of the impossibility of calculating turning radius with changing speed.Once again, based on an engine out.

1106

[john_tullamarine]

no turns are allowed for in the 3rd segment because of the impossibility of calculating turning radius with changing speed.Once again, based on an engine out.

While some companies or jurisdictions may so dictate, there is no engineering reason why a turn can't be scheduled in the third segment.

Two main difficulties arise -

(a) radius of turn - adjust the splay by min/max speed geometry and that problem goes away very quickly

(b) the AFM generally doesn't give any way to adjust for the additional drag (cf reduction in climb gradient during the other segments) - that has to be addressed by some rational means which, by rights, should also involve local regulatory authorisation.

[Balkanhawk]

If i remember correctly the 400ft segment is contained in EU Ops Subpart G - Performance Class A.