330 Derated Takeoff

[dustypfd]

Hi, in the manual under Engine failure after V1 it states 'On derated takeoff do not use TOGA thrust if speed is below F in conf 2 and 3'. Assuming that you happen to be at V2 or thereabouts after engine failure (quite possible),wont you always be below F. In our company we always select TOGA. I would be greatful for any informed input

[Iceman49]

We use flex takeoffs with our Pratt's...we always have the option to go to TOGA, or stay at Flex...however when going to TOGA it seems to input to much adverse thrust.

[Down Three Greens]

It is a minimum control speed issue. New control speeds for what is a essentially a procedure that tells the aircraft it has a different rated engine fitted to the aircraft.

Minimum Control Speeds with Derated Thrust

A given derate level corresponds to the basic maximum thrust reduced by a given percentage. Therefore, the new maximum available thrust at any point of the takeoff flight path is cut back, compared to the non-derated thrust. New minimum control speeds (VMCG, VMCA) can then be established, as per JAR/FAR 25.149. A reduction in the minimum control speeds sometimes generates a takeoff performance benefit (higher MTOW) when taking-off on a short runway. Indeed, the decision speed V1 is the maximum speed at which it is still possible to reject the takeoff and stop the aircraft within the runway limits. Nevertheless, V1 must be greater than VMCG, and the Accelerate Stop Distance is often the most constraining limitation on a short runway. A reduction of the VMCG can then permit a reduction of the ASD for a given takeoff weight, and lead to better takeoff performance when the
MTOW without derate is ASD/VMCG limited.

Derated Takeoff Procedure

Derated takeoff is not available for all Airbus aircraft models. It is basic on all A330 and A340 models, but doesn’t yet exist on the other Airbus aircraft types WRONG...now out of date...see later post...Available on A320 series too!!!. .When derated takeoff is available, 6 certified levels exist, ranging from (TOGA- 4%) to (TOGA–24%) with a constant four percent increment (4%, 8%, 12%, 16%, 20% and 24%)3. This means that the AFM must contain a set of performance data for TOGA, and a set for each derate level (TOGA - X%). To carry out a derated takeoff, the actual takeoff weight and speeds have to be checked against the Maximum permissible takeoff weight computed for the given derate level (specific RTOW chart or equivalent computerized system). The derate level must then be entered in the MCDU (Multipurpose Control and Display Unit) during the takeoff preparation phase. At the brake release point, the thrust throttles must be pushed to the FLX position.

Important: When a derated takeoff is carried out, TOGA thrust must never be
selected until the aircraft is airborne and above the minimum flap retraction speed (“F” speed). The reason for this is that performance calculations are made for minimum control speeds, different from the ones of TOGA.

[dustypfd]

Thanks very much for your replies.I'm afraid im still a little confused.Your post implies that this derate function is not available on the 320.We do flex takeoffs on every departure on the 320! Am i getting these mixed up ie. are they two different things? I assumed derated takeoff was a flex takeoff.

[FlapsOne]

As I understand it in simplistic terms ('cos that's all I'm capable of!) a derate is a (semi-)permanent issue of engineering certification/set-up of an engine which reduces it's thrust capability to something below it's manufactured ability. (eg. 26k thrust derated to 24k thrust). This allows for extension of engine life, slightly different limitations perhaps, maybe different noise category etc etc etc.

A Flex take off is a specific thrust reduction for a specific take off, in addition to the pre-exisiting derate, to take advantage of the conditions (wx) that exist on the day at that airfield on that runway with that weight etc etc.

[dustypfd]

That makes sense and would explain why we still always use TOGA in my airline.It seems the derate is an option separate to flex which we dont have.

[Down Three Greens]

Reduced Thrust i.e. FLEX

JAR OPS AMJ 25-13 / AC 25-13

(4)(c) Reduced takeoff thrust, for an aeroplane, is a takeoff thrust less than the takeoff (or derated takeoff) thrust. The aeroplane takeoff performance and thrust setting are established by approved simple methods, such as adjustments, or by corrections to the takeoff thrust setting and performance.”

“AMJ 25-13 / AC 25-13
(5)(a) The reduced takeoff thrust setting
(2) Is based on an approved takeoff thrust rating for which complete aeroplane performance data is provided
(3) Enables compliance with the aeroplane controllability requirements in the event that takeoff thrust is applied at any point in the takeoff path
(4) Is at least 75% of the maximum takeoff thrust for the existing ambient conditions”

(f) The AFM states that [reduced thrust takeoffs] are not authorised on contaminated runways and are not authorised on wet runways unless suitable performance accountability is made for the increased stopping distance on the wet surface".

JAR OPS “AMJ 25-13 / AC 25-13
(4)(b) Derated takeoff thrust, for an aeroplane, is a takeoff thrust less than the maximum takeoff thrust, for which exists in the AFM a set of separate and independent takeoff limitations and performance data that complies with all requirements of Part 25.” i.e. New charts of raw performance in FCOM 2.

For a derated takeoff, the limitations, procedures and performance data must be included in the Aircraft Flight Manual (AFM). For each derate level, a specific RTOW chart can be established for a given runway, taking into account such new limitations as the minimum control speeds.

Derate = In essence....the aircraft had a different rating of engine fitted for the take-off i.e. 25K of thrust instead of 27K

Flex = Assumed temperature method for reducing thrust.

Flex and Derate cannot be used at the same time.

Can Derate from a contaminated runway but not Flex. Strange as it sounds you can get a higher RTOM off a short contaminated runway using a derated take-off option. This is because the minimum control speeds may limit take off mass in this case. Reduce the supposed maximum thrust of the engines by derate (not flex) you get lower speeds....hence higher RTOM. A few tons in the case of the A320 series.

My appologies but my original post was out of date. Derate option is now widely available on the A320 series.

Flaps One

Engine Rating i.e. CFM56-5B4/P - Permanently sets maximum thrust level. It is a plug in the engine/FADEC.

Derate - Tell the engine you want the engine to behave like a different one - 5B4/P minus 4/8/12/16/20/24% thrust. It is an MCDU input. Thats why you have to preface the Flex Temp with F (F48) in some aircraft...to differentiate from Derate (D12). Performance charts for each derate level.

Flex - Fool the engine about OAT etc.... One performance chart.

Cheers

[titi]

In certain cases you are (in your RTOW) limited by VMCG and/or VMCA because of short runway or contaminated runway.
The possibility to increase your max weight is to change the scenario you are dealing with everyday. That is to change your VMCG or VMCA value.
The only way to do it is to reduce power of the engine (flaps setting and altitude constant).
Normal VMCA and VMCG are calculated based on TOGA power and of course gives a certain yawing moment associated with. If you reduce engine thrust by a certain amount, then with every thrust setting you have new VMCG VMCA value (of course lower).
In that case you are still VMCG VMCA limited but your max toff weight is higher than the one with TOGA.
The other point is engine failure drill:
Why do not set TOGA if you really have an engine failure.
Because the speed you fly at (V2) is or may be lower than normal VMCA (calculated with TOGA power). Remember what happen if you fly near or below VMCA.

[Down Three Greens]

Cheers Titi

Another fall-out from the Derate function....FLEX TEMP NOT SET drill.

On basic aircraft... ECAM demands THR LEVERS.....TOGA

On derate option....Set THR LEVER......IDLE as you may be using derated take-off performance values and TOGA may cause the VMCA/G issues that 'titi' expands on.

Derated takeoff ===> TOGA below -F speed may cause the aircraft to have lateral control issues. Magenta bug V2 bug is defined using the derated V2 not TOGA V2.

[titi]

Agree with u down 3 greens.

[FE Hoppy]

Down Three Greens.
Maybe not on the Bus but:-
JAR OPS AMJ 25-13 / AC 25-13

(4)(c) Reduced takeoff thrust, for an aeroplane, is a takeoff thrust less than the takeoff (or derated takeoff) thrust. The aeroplane takeoff performance and thrust setting are established by approved simple methods, such as adjustments, or by corrections to the takeoff thrust setting and performance.”

Clearly says that Flex and Derate is allowed. This combination is used on other aircraft types.

Otherwise your explanation is spot on.