A320 SOP brake release at takeoff
 

I was made aware that the standard SOP take off sequence calls for power at
50% N1 before brake release(no crosswind),this would preclude a rolling takeoff. I'd like to hear your thoughts.

I'm curious: why would this technique be a manufacturer's decision?

There was a change to the wording but FCOM NORM PROC still states:

"The below procedure is the standard takeoff procedure. However, rolling takeoff is permitted."

So no change really.

CP

Watch the wording , for a static take off SOPs say: Thrust LEVERS......50%N1. I understand it as being the LEVERS in position , and you don't have to wait for actual 50 % of N1 to release the brakes.

Actually you can not set any % N1 with reference only to the Thrust Levers. The FCTM refers to the TLA, Thrust Lever Angle symbol or "doughnut", not the Thrust Levers.

If doing a static take off then set 50 %, wait for engines to accelerate and stabilize, release brakes and set FLX / TOGA.

The FCTM states:

"If cross wind is at or below 20 kt and there is no tail wind
• From idle to 1.05 EPR / 50 % N1 by reference to the TLA indicator on the EPR / N1 gauge.
• When the engine parameters have stabilized, to the FLX/MCT or TOGA detent as appropriate."

Then:

"This procedure ensures that all engines will accelerate similarly. If not properly applied, this may lead to asymmetrical thrust increase, and, consequently, to severe directional control problem."

CP

CaptProp is correct at post #3.
Ref. FCOM PRO-NOR-SOP-12-takeoff
The "below procedure" is the 50%N1 prior to brakes release.

I totally disagree , what you quoted from FCTM has nothing to do with power on brakes but more of having engines stabilized at 50 % of N1 before applying Flex or toga

Power on brakes will not save you from directional problem if both engines are not stabilized at 50% of N1 . This can happen with two different mounted engines , called intermix engines. Spool up time is different and you have to wait for both engines stabilized at 50% being on brakes or not.

If brakes can save you from a directional control ? Why rolling take off is allowed ? you apply immediately 50% of N1 , if you fear a directional control problem , that could happen to an aircraft spooling up not on brakes , I would be more concerned for an aircraft already rolling at lets say 10 kts , with an assymetry.

Having an N1 assymetry with an aircraft already rolling would be more difficult than an aicraft in standstill.

As an analogy for the 180 on the runway SOPs say: "On ENG 1, set N1 to between 30 % and 35 % (CFM engines).."

Here talking about actual N1

When Airbus say Thrust , they mean Thrust . When they say Thrust LEVERS it means Thrust LEVERS.

As you wonderfully quoted FCTM which is a guidance for flight crew on how to perform procedures , it says regarding take off:

The PF should announce "Take-off". The PF then applies power in as follows: If cross wind is at or below 20 kt and there is no tail wind • From idle to 1.05 EPR / 50 % N1 by reference to the TLA indicator on the EPR / N1 gauge. • When the engine parameters have stabilized, to the FLX/MCT or TOGA detent as appropriate.

Not talking about brakes

You are correct. "Both ENG N1 at 50% ....... STABILIZE" would be the line to expect and definitely it is not there. Either Airbus is getting sloppy, or I have been indeed reading this wrong.

thanks,
FD.

Citation2, you may not agree but in my opinion this is how Airbus intended the procedure to be applied.

From the AFM:

"Apply 50 % N1 on both engines with brakes on.
Note: Brakes may be released so as to perform a rolling takeoff.

If crosswind at or below 20 kt and no tailwind: Release brakes with stick half forward. Apply thrust up to the FLX/TOGA thrust whilst maintaining stick half forward up to 80 kt."

At the end of the day they leave it up to you to decide by adding the note. However, they have made the brakes on until 50% the "standard" takeoff procedure but still left it up to the crew to make rolling takeoffs when required for operational reasons, for example when cleared line up and immediate takeoff due to traffic on final.
The most important thing in my opinion, brakes on or off, is to make sure engines are spooled up properly and stabilized at 50% before setting FLEX / TOGA. I've seen a few colleagues doing, what I think is a bit too sporty takeoffs, where the spool up towards 50% was slightly uneven and where they've not waited long enough for engines to catch up with each other before applying FLEX. Result is a very wobbly and unstable initial takeoff roll.

CP

I think it is setteld now. CaptainProp, thanks for being thorough and going all the way.

AFM: http://i61.tinypic.com/2qsxn47.png

FD.

From AFM INTRODUCTION:

"This Airplane Flight Manual (AFM) is a reference document published in English. iT IS NOT ESTABLISHED AS AN OPERATIONAL DOCUMENT TO BE USED DIRECTLY BY THE CREW IN FLIGHT. Flight crew documents available in flight must include an Operational Manual, with appropriate contents and language as required by the National Regulations."

Now what are you going to follow FCTM , FCOM or AFM?

I have a better one : maximum tailwind for take off and landing on AFM it says 10 knots, on FCOM maxi tailwind is 15 kts. Which one do you apply?

And I will pass on the differences between AFM and FCOM as this is not the subject here

FCOM clearly says thrust levers. AFM clearly says apply N1 50% of N1. Still my reference document is the Flight Crew Operating Manual where it clearly states Levers.

The fact that the aircraft was demonstrated and gained certification probably in the most restrictive conditions does not constitute a procedure itself for flight crew , our reference is and will remain the FCOM.

Why did Airbus change the wording between AFM and FCOM , why the wording used in FCOM is different ? Simply because they mean otherwise

You can interpret it any way you like, but the operator's OM-B overrides any FCOM statements.

At my outfit, the SOP has been brought in line with the Airbus recommendation to achieve 50% thrust before brakes release on a STATIC take-off, rolling take-off is permitted however.

So waiting on the runway for T/O clearance, use the static method. Otherwise, use the 'old' method. If it differs in your company ops manuals, just do what they say. But they will usually override the FCOM if different.

Citation2, if you already knew the answer and had made up your mind how to interpret the issue, why then ask the question here?

From AFM Normal Procedure Introduction:

"The procedures contained in this chapter have been established and are recommended by the aircraft manufacturer. Only particular operations which are considered useful to highlight are presented. The procedures which are considered to be "basic airmanship" are therefore not covered. When actions depend on a condition, a black dot (•) or a black square (■) identifies this condition. The black square is used when there is a choice between one or more conditions and only one is applicable. These procedures are approved by the Airworthiness Authorities as acceptable procedures for a convenient use of the aircraft. This approval does not prevent the operator from developing equivalent procedures provided these procedures are approved by appropriate operational authorities."

Cood luck with your takeoffs.

CP

As far as the limitations are concerned the AFM is the main reference. Regarding the tailwind if your FCOM says 15 kt for landing you better go and check the AFM: APPENDICES AND SUPPLEMENTS and look for TAILWIND OPERATION chapter that will allow you to use 15kt for landing.

I think we do need to be a bit careful here. Usually there is a hierarchy of manuals published that goes something like Notices To Crew, OEBs, OMs, FCOM.. and in case of any conflict you should apply the guidance of the highest in the list. However, taking the most conservative limits shouldn't ever be considered a bad strategy, until that limit is expressly clarified by the operator for which you work.

In the case of a tailwind limitation, such details form part of any initial LCP/OPC so there should never really be any doubt. If there is, then Citation2 you really need to talk to your new colleagues before operating.

The AFM NORM-TO describes a static takeoff with the application of 50% N1 on both engines and with the brakes on: the main reason is that takeoff performances are calculated by this method for certification.
Thus, as we compute takeoff performances from a full stop position, brakes must be kept until 50% N1.

Note that however, rolling takeoff is permitted on Airbus aircraft.

Thanks for completing my statement. Absolutely agree. What I had in mind was only the legal basis for the certain limitations stated in the FCOM which are available as "optional" and must be supplemented in the AFM.

No problem, just wrote it out in case Citation wasn't aware. He/she seemed a bit unsure about which to apply first, and for an A320 I'd be surprised, but mainly worried!- if his employer didn't have a set of OMs to guide him/her.

Just to make sure, everyone agrees that AFM must be complied with irrespective of FCOM / FCNs / OMs / FCTM etc, right? :eek:

FD.