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My appologies but my original post was out of date.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
Last edited by Down Three Greens; 6th November 2006 at 10:12.