MCDU - Thrust Reduction / Engine Out Alt.

[Scallywag]

I've tried FCOM 4 and all the other usual places, but can't find the answer to this one.

Why are "Thrust Reduction" and "Engine Out" sometimes different by a few feet(typically 30 -100 ft) and at other airfields exactly the same as one another in the MCDU. I understood they normally defaulted to 1500ft above aerodrome level, or is one the aerodrome datum and the other the threshold elevation or something cunning like that. I only ask because it never used to be like that in the MCDU database, I always recall them being identical until the last few months. Can anyone help ?

[QAVION]

"I only ask because it never used to be like that in the MCDU database, I always recall them being identical until the last few months."

What sort of plane are we talking about here, Scallywag? As a 747-400 maintenance engineer, I set up the default values on the FMC MAINT Perf Factors page after I've updated the Nav Database (every 28 days). If the values have changed and you haven't been told about it, perhaps your Maintenance dept. have stuffed up? Do you have a list of default values in your manuals/Tech Log.
From memory, the values return to the defaults at the end of the flight, but I'll have to confirm this.

Rgds.
Q.

[Zeke]

Qavion:

You will get educated in due course when the A330s are in service with QF that on a Airbus you have a FMGC and MCDU, 744 Boeing speak is not applicable to this question (i.e. the FMC question on the 767). :rolleyes:

Scallywag:

The answer to your question is in the Honeywell A320 FMS Pilots guide Pg 3.2-64. While this manual does not cover your question 100% the A330/A340 are similar (slightly different MCDUs).

During preflight the Thrust Reduction/Acceleration Altitude values are displayed in blue small text on 5L on the takeoff page with a default value of 1500 ft above the departure FIELD elevation.

They are modifiable by the pilots preflight, but not once the takeoff phase has achieved by the FMGC.

My suggestion for the difference is for a departure RUNWAY where an EO SID is in the database for that RUNWAY (ie not FIELD) that requires some special routing. To meet the single engine terrain clearance requirements.

For example the Jeppesen A320 Airport Analysis Manual for Mexico City (CFM 56-5A3 engine) has a range of thrust reduction values, and has a special procedure for the airport. Runways 05L/R require a 15 deg banked climbing turn at 5.0 DME MEX to 320 degrees intercepting and tracking on the 360 MEX VOR radial, 23L/R same turn requirements but at 5.4 DME MEX, direct MEX VOR, continue climb on the 360 MEX VOR radial.

RWY 05L Min Acceleration Height 800 ft
RWY 05L Max Acceleration Height 2445 ft

RWY 05R Min Acceleration Height 800 ft
RWY 05R Max Acceleration Height 2010 ft

RWY 23L Min Acceleration Height 1200 ft
RWY 23L Max Acceleration Height 2048 ft

RWY 23R Min Acceleration Height 1198 ft
RWY 23R Max Acceleration Height 2024 ft

I understand that the difference between these heights is due to the Obstruction limit weight requirements of FAR 121.189.

Cheers

Z

[mutt]

Qavion,

(744-400) Can you please explain this procedure to me I set up the default values on the FMC MAINT Perf Factors page after I've updated the Nav Database (every 28 days).

After jumping from Avionics maintenance to Honeywell to Boeing to Honeywell to Avionic maintenance etc, I was firmly put under the impression that Boeing was the only people able to adjust our PERF defaults. We use the defaults of 1000 feet all engine and 800 feet engine out, if you do have a procedure to physically adjust these, could you please give me a maintenance manual page reference.

Zeke

I could never work out how Airbus calculated anything, but I would say that the difference in the two heights is because the minimum acceleration height is just getting you over the obstacle. The maximum acceleration height is actually an extended second segment climbing at takeoff power to the 5 (or 10 ) minute takeoff thrust limit.

Mutt ;)


[This message has been edited by mutt (edited 08 March 2001).]

[Scallywag]

Thanks Zeke, sounds reasonable

Scally

[slam_dunk]

On a 747-400 E/O accelleration height, flap accel ht etc. can be changed while on the ground :
- go to : init ref index
- LSK 6R : Maint
- LSK 2L : Perf Factors
- type "ARM" and insert in LSK 6R
now you can change the performance data like E/O acceleration height, etc.

good flying !

[mcdhu]

I think that the default values are different when the airfield elev and that of the r/w in question are different. This hypothesis seems to work in the 320/1 both cfm and v2500. Hope this helps.

[mutt]

Guys,

Thanks for your inputs.

Mutt

[This message has been edited by mutt (edited 12 March 2001).]

[O\ZON]

Mutt
your mostly correct re explaination for min and max acceleration altitude.
except max acceleration is limited by 5 or 10 minute thrust reduction to end of THIRD segment (accleration segement).

However at high altitude airports (Bogota) with high obstacles, airbus software gives max acceleraion altitude lower than the minimum acceleration altitude......
software gets confused and gives an output of:
Min accel height: *****
Max accel height: *****

Trying sticking that into to your onboard systems