B737/ B727 AFM limitation on thrust increase with engine failure.
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B737/ B727 AFM limitation on thrust increase with engine failure.
My understanding is that if an engine failure occurs after V1 while conducting a reduced thrust (assumed temperature method) takeoff, the pilot may increase thrust on the live engine at his discretion. The B737 FCTM states If conditions are encountered during take off where additional thrust is desired, such as windshear or temperature inversion, the crew should not hesitate to manually advance the thrust levers to maximum rated thrust.
I do not have a 737 AFM at hand, but I understand that many years ago, the AFM specifically prohibited use of increased thrust if encountering an engine failure on take off while conducting an assumed temperature reduced thrust take off. My recollection was that there was an incident to a Boeing 707 where the pilot increased thrust on the three remaining engines after an outboard engine failed during a reduced thrust take off and the resulting additional yaw nearly caused loss of control.
Does the AFM for B737 Classics and NG still have this FAA imposed limitation?
I do not have a 737 AFM at hand, but I understand that many years ago, the AFM specifically prohibited use of increased thrust if encountering an engine failure on take off while conducting an assumed temperature reduced thrust take off. My recollection was that there was an incident to a Boeing 707 where the pilot increased thrust on the three remaining engines after an outboard engine failed during a reduced thrust take off and the resulting additional yaw nearly caused loss of control.
Does the AFM for B737 Classics and NG still have this FAA imposed limitation?
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Not to my knowledge - I have often taken into consideration the effect of going to full power with a V2 from a greatly reduced power setting, but not having Vmca to hand I have to assume Boeing has taken it into account? Could this be the reason for the Boeing % limit to reduction that should be applied?
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The FAA order generally authorizing reduced thrust (late 70's - I cannot recall its number just now) specifically stated that the crew could advance the good engine(s) to rated thrust at any point in the takeoff without adverse effect. Flight test was required, I believe, to certify this characteristic.
It would be hard for me to accept that FAA backed down from this rule. The current rule is Order 8000.39, but I'm unable to find a complete copy online.
It would be hard for me to accept that FAA backed down from this rule. The current rule is Order 8000.39, but I'm unable to find a complete copy online.
Last edited by barit1; 18th Sep 2005 at 01:17.
We normally assume that a reduced thrust take off (not runway / obstacle limited) considers the climb performance and aircraft handling, thus there should not be any requirement to increase thrust, but if the crew elect to do so then there should not be any handling problems.
However, if a reduce thrust take off is chosen specifically to reduce V1 (runway length limited) by reducing Vmcg, then there might be reason to reconsider any other effects if full thrust were to be applied after an engine failure. If V2 is also rescheduled to a lower value, as a function of a reduced V1, then the Vmca considerations might also have to be reconsidered. (JAR/FAR 25.125 / 25.149).
Thus as speculation/debate, any restriction on increasing thrust or not, might be taking the latter point into consideration and some of the reasons for this are in the definitions of ‘Reduced Thrust’ and ‘Derate’.
AC 25-13 'Reduced and Derated Takeoff Thrust Procedure' (note date – 1988) and AC120-62 appear to support the observation above:
AC 25-7A Flight Test Guide for Certification of Transport Category Airplanes, also appears to supports this view (Para 91 and Appx 4).
Thus aircraft using an assumed temp reduced thrust may have no restriction on increasing thrust, but derated operations might have; is this the difference seen in the manuals?
Link to FAA ACs / search
However, if a reduce thrust take off is chosen specifically to reduce V1 (runway length limited) by reducing Vmcg, then there might be reason to reconsider any other effects if full thrust were to be applied after an engine failure. If V2 is also rescheduled to a lower value, as a function of a reduced V1, then the Vmca considerations might also have to be reconsidered. (JAR/FAR 25.125 / 25.149).
Thus as speculation/debate, any restriction on increasing thrust or not, might be taking the latter point into consideration and some of the reasons for this are in the definitions of ‘Reduced Thrust’ and ‘Derate’.
AC 25-13 'Reduced and Derated Takeoff Thrust Procedure' (note date – 1988) and AC120-62 appear to support the observation above:
4. b Derated takeoff thrust, for an airplane, is a takeoff thrust level less than the maximum takeoff thrust, for which exists in the AFM a set of separate and independent, or clearly distinguishable, takeoff limitations and performance data that complies with all the takeoff requirements of Par…. When operating with a derated takeoff thrust, the value of the thrust setting parameter which establishes thrust for takeoff is presented in the AFM and is considered a normal takeoff operating limit.
c. Reduced takeoff thrust, for an airplane, is a takeoff thrust less than the takeoff (or derated takeoff) thrust. The airplane takeoff performance and thrust setting are established by approved simple methods, such as adjustments, or by corrections to the takeoff or derated takeoff thrust setting and performance. When operating with a reduced takeoff thrust, the thrust setting parameter which establishes thrust for takeoff is not considered a takeoff operating limit.
This definition is expanded in AC120-62 “ … the thrust may be restored to the maximum level (or derate) as appropriate for the conditions of the flight at any time during the takeoff. i.e reduced thrust can be lower than a fixed derate
5. b. Relevant speeds (VEF, VMC, V1, VR, and V2) used for reduced thrust take offs are not less than those which will comply with the required airworthiness controllability criteria when using the takeoff thrust (or derated takeoff thrust, if such is the performance basis) for the ambient conditions, including the effects of an Automatic Takeoff Thrust Control System (ATTCS), It should be noted, however, that in determining the takeoff weight limits, credit should not be given for an operable ATTCS.
c. Reduced takeoff thrust, for an airplane, is a takeoff thrust less than the takeoff (or derated takeoff) thrust. The airplane takeoff performance and thrust setting are established by approved simple methods, such as adjustments, or by corrections to the takeoff or derated takeoff thrust setting and performance. When operating with a reduced takeoff thrust, the thrust setting parameter which establishes thrust for takeoff is not considered a takeoff operating limit.
This definition is expanded in AC120-62 “ … the thrust may be restored to the maximum level (or derate) as appropriate for the conditions of the flight at any time during the takeoff. i.e reduced thrust can be lower than a fixed derate
5. b. Relevant speeds (VEF, VMC, V1, VR, and V2) used for reduced thrust take offs are not less than those which will comply with the required airworthiness controllability criteria when using the takeoff thrust (or derated takeoff thrust, if such is the performance basis) for the ambient conditions, including the effects of an Automatic Takeoff Thrust Control System (ATTCS), It should be noted, however, that in determining the takeoff weight limits, credit should not be given for an operable ATTCS.
Thus aircraft using an assumed temp reduced thrust may have no restriction on increasing thrust, but derated operations might have; is this the difference seen in the manuals?
Link to FAA ACs / search
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Ah yes - the old distinction between REDUCED (aka flex or assumed temp) and DERATED (as in separate AFM tables). As I recall, derated performance may be used on a contaminated runway, but reduced thrust may not.
Or at least that was true under the old FAA order. Is it still the case?
Or at least that was true under the old FAA order. Is it still the case?
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could advance the good engine(s) to rated thrust at any point in the takeoff without adverse effect
You are permitted to advance the thrust to the "RATED" thrust without encountering any adverse effects, however this only applies when you are using Reduced Thrust with either the Assumed Temperature Method or Flex Thrust. The VMCG is always based at actual temperature to provide you with the required protection.
If your aircraft is operated with Fixed Derates such as TO/TO-1/TO-2, you will not be protected if you advance thrust from a TO-2 ATM to TO at actual temperature.
Barit1, that rule still applies.
Mutt
You are permitted to advance the thrust to the "RATED" thrust without encountering any adverse effects, however this only applies when you are using Reduced Thrust with either the Assumed Temperature Method or Flex Thrust. The VMCG is always based at actual temperature to provide you with the required protection.
If your aircraft is operated with Fixed Derates such as TO/TO-1/TO-2, you will not be protected if you advance thrust from a TO-2 ATM to TO at actual temperature.
Barit1, that rule still applies.
Mutt
