Acceleration height

[Richard McDonald Woods]

I am unsure how to set realistic acceleration heigths for take-off.

British Airways set flaps 20 for B744 take-offs. However, I can find no information on how to decide the acceleration height. Presumably there are both airline standards and airport considerations for noise abatement to be considered. But what mix is correct? And where are the airport/runway acceleration heights stated?

[Mundyas]

Hi Richard

Just been looking at a very old SID (Standard Instrument Departure) plate for London Gatwick dated 24 Feb 00.

Amongst all the information it mentions for the Southampton and Kenet SID "5. Cross noise monitoring points {see C3} not below 1200, then maintain climb gradient 4% to 3000." So I think it is saying 1200 is the acceleration height after noise abatement for this departure.

So might be a good idea  to obtain departure charts of your takeoff airport and follow the procedure for a given departure.  

Handling the Big Jets by D P Davies a great book in my humble opinion mentions inter alia Noise abatement techniques and the segments involved.

 He gives a typical noise abatement departure profile. Paraphrasing somewhat {and the pilot is flying the noise abatement manually, we do not have to do this on the !-! simulation}.

(1) First segment - gear up, take off flap, full power, V2 + 15 knots.
change to second segment - simply throttle back to reduced power.
(2) Second segment - take off flap, reduced power, V2 + 15 knots.
End of noise abatement. Restore climb power.

Hope this helps.

Would be interested in hearing from a 744 pilot as would like more details as well. Flight Manuals etc.
Regards Andrew

[Richard McDonald Woods]

Andrew,
Many thanks for your thoughts. I have a problem, though.

At EGLL, for example, each SID publishes both a vertical and horizontal profile for departure routes. On the current BPK6J SID for runway 06R (from Navigraph and UK AIP), it states a routeing of "Climb on 092 degrees, at D2 LON turn left 052 degrees, R073 LON, at D10 LON turn left 018 degrees/radial 198 BPK, BAPAG, BPK" and altitudes as "D10 LON MNM 3000, D10 BPK MNM 4000, D6 BPK at 6000, BPK at 6000".

The minimum climb gradient is stated as "Cross noise monitoring points not below 1100, then 4% up to 4000 ft. If unable to conform to the published gradient/SID altitudes, inform ATC prior to departure".

Now, I could infer that acceleration heigth is 1100 ft or 4000 ft, although I would discount the latter because of the "D10 LON MNM 3000" of the altitude profile required. But I still have nothing referred to as acceleration height.

[Mundyas]

Hi again Richard

I have now looked at the old reliable standby the manual supplied by HH.

Page 159 Flap / Acceleration Height Line. Displays entered take off flap setting and indicates acceleration height at which VNAV guidance decreases pitch to accelerate towards 250 knots or Vref +100.

I am very aware of my lack of know how here! And I could be totally wrong!

But I think when you enter the route into the FMS (you mention) and enter weights and V! etc all calculated and inputed etc. Then the route is "set" in the FMS with speeds set in each part of the route. So inputing flaps 20 in the Take Off Reference Page would produce/calculate  the appropriate acceleration height. The acceleration height can also be manually input if required.

In the real world BA would have preloaded routes available for a  departure routes (like the one you mention) and an appropriate acceleration height for the conditions would appear on the take off reference page when flaps 20 was input.

Really need a line pilot to help here.

Hope haven't confused more.

Andrew

[Phil Bunch]

Just to add a bit of humor into this very interesting technical discussion:

I have a distant memory that Captain Tarmack once described how he needed to ferry a mostly empty 744 from airport A to airport B.  He described (at least according to my distant memory) how amazed the tower was when the 744 seemed to leap off the runway part-way across its length and then climbed semi-vertically, reaching a surprising altitude before clearing the end of the runway.  At least that's how my aging memory recalls his colorful description.

(I hope this isn't one of those instances where various conversation threads got mixed up together and synthesized a false memory!)

Even if this ancient memory isn't fully accurate, how fast could an empty 744 climb after takeoff?

[jtsjc1]

Reading Capt. Mike Ray's check ride manual, the 744 is a rocket when its light. And apparently very nimble when not fully loaded.

[G-CIVA]

I can find no information on how to decide the acceleration height.

You never kept copies of the BAv B744 Manual that I did then?

 

BA have some very stringent rules regarding B744 take offs which are very different to most other 744 operators.  

They also have to adhere to any ARPT specific rules (e.g as covered in Jepp Plates 10-1 series).

They have developed their own specific Noise Abatement Departure for the B744 which has evolved over the years...the name of the game being to keep the ENG core temps to a minimum thus increasing 'on the wing' engine life & placing the aircraft in an intermediate climb configuration where the noise footprint on the ground is mitigated by the climb gradient.

Some general BAW Take Off Rules

Flap 20 for ALL Take Offs

Packs OFF for all Take Offs above 300t (these used to be performed with Pack 2 to APU & Pack 1 & 3 OFF with ISOL Valves closed) but it's been Packs off for a few years now.

Packs go back ON again (one at a time after CLB Power set) passing the THR RED ALT.

The BAW Noise abatement departure is as follows:

-------------------------------------------------------------------------------

1.  Carry out the standard takeoff procedure up until 1000ft AAL.

2.  At 1000ft AAL reduce power to full CLB power.

3.  Speed Intervene to Flap 10 minimum maneuvering speed plus 10kts.

4.  Accelerate to Flap 10 minimum maneuvering speed plus 10kts, retracting flaps to 10 on schedule.

5.  Climb in this configuration until the terminating altitude listed on the chart.

6.  Terminate speed intervention & accelerate on schedule to en-route economy climb speed.

7.  Once clean, reduce climb power to CLB1.
-------------------------------------------------------------------------------

The minimum climb gradient is stated as "Cross noise monitoring points not below 1100, then 4% up to 4000 ft. If unable to conform to the published gradient/SID altitudes, inform ATC prior to departure".

Now, I could infer that acceleration heigth is 1100 ft or 4000 ft, although I would discount the latter because of the "D10 LON MNM 3000" of the altitude profile required. But I still have nothing referred to as acceleration height.

A 4% climb gradient is 243ft/NM or ...

@ 180 kts its is 730fpm up to 851fpm @ 210kts**

At LHR the ACCEL/THR RED ALT is 1000ft aal.

The Terminating ALT for the SPD INTV @ F10 +10kts is 4000ft aal - that then concurs with the requirement to maintain a minimum 4% climb gradient from 1100ft to 4000ft.

You can see it all happening on this vid...CLB Thrust is at approx 03:10:

http://youtu.be/HL2uDPh1Z4o

QF at AKL & it looks like CLB Thrust as set with Flap 5 at approx 02:10:

http://youtu.be/d6O1cZvp3XA

Obviously different airports have different rules & the ACCEL/THR RED ALT &/or Terminating ALT may change to reflect specific requirements...this is covered in the various briefing tools available to the crew on the flight deck.

BAW also encourages acceleration to the ECON CLB SPD (above VREF +100kts where ATC will allow) ASAP after cleanup (for obvious reasons).

AFIK they still CLB @ CI 0 & CRZ @ CI 90 - this might have changed in line with the ever increasing cost of fuel & I'll do my best to cfm it.

Where any noise abatement procedures are not required BAW specifies the following parameters on the TO REF Page of the CDU:

-------------------------------------------------------------------------------

FLAP/ACCEL HT line - 20/1000

E/O ACCEL HT line - 1000

THR REDUCTION HT line - FLAPS 5  

-------------------------------------------------------------------------------

Lots of ARPTs around the world specify specific noise abatement profiles & often these are either NDAP 1 or NDAP 2 profiles:

NADP 1 (Noise Abatement Departure Procedure 1)

This procedure involves a power reduction at or above the prescribed minimum altitude and delaying flap/slat retraction until the prescribed maximum altitude is attained.
At the prescribed maximum altitude, accelerate and retract flaps/slats on schedule while maintaining a positive rate of climb and complete the transition to normal en-route climb speed.
The noise abatement procedure is not to be initiated at less than 1500 feet AGL.
The initial climbing speed to the noise abatement initiation point shall not be less than V2 + 10 knots.
On reaching an altitude at or above 1500 feet AGL, adjust and maintain engine thrust in accordance with the noise abatement thrust schedule provided in the aircraft operating manual.
Maintain a climb speed of V2 + 10 to 20 knots with flaps and slats in the take-off configuration.
At no more than an altitude equivalent to 3000 feet AGL, while maintaining a positive rate of climb, accelerate and retract flaps/slats on schedule.
At 3000 feet AGL, accelerate to normal en-route climb speed.

NADP 2 (Noise Abatement Departure Procedure 2)

This procedure involves initiation of flap/slat retraction on reaching the minimum prescribed altitude. The flaps/slats are to be retracted on schedule while maintaining a positive rate of climb. The thrust reduction is to be performed with the initiation of the first flap/slat retraction or when the zero flap/slat configuration is attained.
At the prescribed altitude, complete the transition to normal en-route climb procedures.
The noise abatement procedure is not to be initiated at less than 1500 feet AGL.
The initial climbing speed to the noise abatement initiation point is V2 + 10 to 20 knots.
On reaching an altitude equivalent to at least 1500 feet AGL, decrease aircraft body angle whilst maintaining a positive rate of climb, accelerate towards Flaps Up speed and reduce thrust with the initiation of the first flaps/slats retraction or reduce thrust after flaps/slats retraction.
Maintain a positive rate of climb and accelerate to and maintain a climb speed equal to Flaps Up speed + 10 to 20 knots till 3000 feet AGL.
At 3000 feet AGL, accelerate to normal en-route climb speed.

At the end of the day its all down to the aircraft operators, airport requirements & on occasion agreement between operators & airport operators/regulating authorities.

Hope this helps.

[G-CIVA]

Even if this ancient memory isn't fully accurate, how fast could an empty 744 climb after takeoff?

A cliche but I do have a friend who works @ BA MX in Cardiff & he can testify to often watching BAW 744s depart empty following MX using full TO Thrust...it must be a sight to behold.

[Richard McDonald Woods]

Hi Steve,

Many thanks for your most helpful reply. No, I foolishly did not retain the BAW manuals.

All I have to do now is to turn your words into my understanding, and then to practice it until it becomes second nature.

Glad you have shown me a little more of the art of flying our beloved B744.