10 minute Thrust -v- Extended Second Segment
 

Hi All,

Can anyone help with this one please?

For the 737NG, it appears that using 10 minute take-off thrust time limit compared against extended second segment with 5 minutes thrust gives the same limiting performance weight. If this is the case, why would one pay for the 10 minute AFM entry, when you could use extended second segment instead? Could it be to do with the requirement to have 1.2% gradient capability above 400ftAAL?

Thanks in advance.

For the 737NG, it appears that using 10 minute take-off thrust time limit compared against extended second segment with 5 minutes thrust gives the same limiting performance weight

I have no ops background with the NG but I can't see there being all that much difference at the coalface between the NG and other twins. I suspect that your statement is taken selectively out of context. The differences will be seen particularly for later obstacle considerations .. are you just looking, say, at first/second segment problems ?

Are you able to provide some AFM evidence to support your statement and then we can, perhaps, offer a comment or two ?

Could it be to do with the requirement to have 1.2% gradient capability above 400ftAAL?

Perhaps it's just a slow start morning for me .. but which particular requirement are you citing here ?

No it does not. It depends mostly on obstacle clearance and only in some cases. The difference is to be able to use the thrust for more than 5 minutes, ever so much a factor when flying in mountainous regions where obstacle clearance is key. Think about a very heavy aircraft taking off towards a range of high terrain, no option to perform an airborne turn thus required to climb above the terrain. By not requiring the aircraft to reduce to climb power much later (compared to same high MFRA) and while maintaining throughout this climb the takeoff weight can be increased for the same profile.

As per above, to facilitate higher takeoff weights for same conditions in predominantly high terrain airports which need to clear these obstacles where the duration of full climb thrust is key to clearing the obstacles.

No, more so with the requirement to clear terrain.


BTW: be careful when performing these calculations unless your tools are correct. Being performance files should be used for these calculations are very specific. It is not always (easily) possible to enable calculations by simply changing a setting (e.g. 5-10 minutes) unless the provided file from Being allows you to compare both.

Nothing stops you from taking extended 2nd segment with the 10 min T/O thrust as well, which would be the main benefit I imagine anyway.

At the beginning of the 4th segment, you have to be with flaps retracted and thrust at MCT, so thereafter any extension in the T/O thrust time has no effect. If you simplify a bit and consider that 1st and 3rd segment are equal in both cases, you see that the 10-min T/O thrust enables you much longer 2nd segment, which means you can clear higher obstacles.

If any of that makes sense, anyway...

Nothing stops you from taking extended 2nd segment with the 10 min T/O thrust as well

Main problem with either time limit is the AFM limitation .. the takeoff thrust setting has to get you to the end of the third segment so there will be limits on the extent to which you can stretch the second segment. The extended time limit helps out significantly.

I am not a Boeing guy but the concept is generic.
By the end of the 3rd segment (level acceleration) Maximum Continuous Thrust would be selected. The Maximum Engine Out Acceleration Altitude (beginning of 3rd segment) is thus defined by the TOGA time-limit.
The Engine Out Acceleration Altitude can not be lower than 400ft by design (ref: ICAO doc 8168) however most companies have a company default which then becomes the nominal minimum. When there are limiting obstacles for a specific runway which infringe the nominal Level Acceleration Segment (3rd segment) you may find that that the EOAA is increased above the company default, but it would need to be a serious increase for the EOAAmax to become a factor.
As the others have pointed out: a 10-min TOGA limit could increase RTOW in the case of an extended 2nd segment, i.e. limiting obstacles infringing the company default EOAA leading to an increased EOAAmin. I expect this to be the case only from very specific runways with high density altitude.

PS: the 1.2% is the final segment/4th segment, which is based on Max Continuous thrust anyway, so not relevant in this context.

I think that the 10 minute T/O thrust limit in case of EFATO would be very helpful as density altitude gets higher. We found it useful for JNB on the B744.

PS: the 1.2% is the final segment/4th segment, which is based on Max Continuous thrust anyway, so not relevant in this context.

As I presumed ... I was querying the 400ft reference .. which although the minimum, is not relevant to an extended second segment.

Exactly what I was referring to, think of mountainous terrain such as the Alps and airports in the foothills surrounded in all directions. Most normal operations do not require 10 minute limitation but sometimes it is required on certain runways at MTOW.

The Gulfstreams that have the 10 minute T/O thrust limit have a big advantage at Aspen, Colorado.