737 CL & NG MCT (CON) for Normal use

[ImbracableCrunk]

I've heard varying opinions on whether MCT or CON is for non-normal situations when it is greater than CLB, specifically in climbs where CLB is less than CON.

I can't find anything in the AFM that expressly prohibits CON for normal usage, but I've read in Boeing's Transport Performance Methods that CON is for emergency use only.

Maybe FAR Part 25? I'm looking for something explicit. Preferably something with "Boeing" and "737" on the cover.

[BleedingAir]

Hmmm... well I don't have a specific reference for you, but I am looking at a company tech bulletin on high altitude speed management which states selection of CON as the N1 limit during the cruise is a Boeing-recommended technique to assist speed recovery at high altitude. It's not mandatory, but is an accepted and approved practice at the operators I'm familiar with.

[D-OCHO]

@BleedingAir: It all depends on wich FMC sofware version you use. But yes you are correct. For older versions Boeing recommends using CON, at cruise, for faster Thrust Lever responds at high altitudes.

[ImbracableCrunk]

Thanks. I should be more specific.

When CON is greater thanCLB is my question. For climbs, not cruise, eg. low-level restrictions for at or above on SIDs.

[Derfred]

I can't answer your question, but I do have a question for you - in what situation is CON greater than CLB thrust? I've only ever seen them being the same (although I probably have never paid much attention at low levels - perhaps that is when it occurs).

[Chesty Morgan]

Usually below 15odd000', especially if in reduced climb.

I use it for expediting or meeting level restrictions. No limits on its use as far as I know.

[vilas]

There is a post by barit1 in 2008 if you can locate it.

[Skyjob]

...in climbs where CLB is less than CON...
Usually below 15odd000', especially if in reduced climb.

You've just answered the OP question to the reason when it exists, in REDUCED thrust settings only, as above 15000' full thrust is always available.

Regarding OP question, selecting CON/CLB merely in this scenario gives you FULL rated thrust, thus is NOT limited to non-normal situations. In fact, when cleared to climb above 15000' it makes sense to expedite the climb using the full available power, taking into account closure rates of course to avoid unnecessary TA/RA's.

[Chesty Morgan]

I was responding to Derfred.

[ImbracableCrunk]

You've just answered the OP question to the reason when it exists, in REDUCED thrust settings only, as above 15000' full thrust is always available.

Regarding OP question, selecting CON/CLB merely in this scenario gives you FULL rated thrust, thus is NOT limited to non-normal situations. In fact, when cleared to climb above 15000' it makes sense to expedite the climb using the full available power, taking into account closure rates of course to avoid unnecessary TA/RA's.

Skyjob,

CON and CLB are not the same, although they may match. Note that with U11.0, the limit in cruise reverts to CLB now, not CON.


From Boeing's Jet Transport Performance Methods:

maximum continuous thrust

This is the third of the “certified” thrust levels.

Maximum Continuous Thrust, or MCT, is a special thrust rating that is only usable in the event of some emergency situation. It may not be used in normal operation. *2 MCT is the greatest amount of thrust that can be used in flight, with the exception of takeoff and landing.

*2. For some engines, the maximum continuous thrust rating is the same as the maximum climb thrust rating; in those cases, this statement does not apply

[vilas]

What Crunk has written is true. TOGA and MCT are for specific purpose. TOGA also can be used for 5mts but if you won't use it for ATC requirements then same applies to MCT. Barit1 an engineer had written that there is issue of warranty with repeated use of MCT with AEO.

[RAT 5]

One could surmise that 'continuous' should be changed to something else. To most of us, without an in-depth knowledge of all the tech manuals, it is not surprising that simple pilots use the dictionary definition.

[donstim]

The FAA's view is "is to always have available the highest thrust
selected by the applicant and certified for continuous unrestricted operation." Also, " The airworthiness requirements do not recognize emergency ratings for fixed-wing
aircraft." These quotes are from a relevant FAA policy statement available here: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/b4c6c780ec6e10e186256bf40070ace1/$FILE/2000-00112.pdf

[Lancelot de boyles]

By simple logic, in the cruise, simply selecting CON as the thrust limit is not the same as operating the engines at that thrust limit. However, should the need arise, the thrust is available; It did occur on a few occasions where the auto thrust went to the thrust limit due to turbulence and a loss of speed, just as it would with CRZ or CLB selected.
Is there any change in A/T response with CON selected?

With a previous North American operator, it was SOP to select CON in the cruise, although with another JAA operator it wasnt considered.

With a red nosed outfit, in the climb, once above about 6000' or 7000', it became common practice to delete the CLB-1 restriction, and get full climb thrust. Generally gaining a few extra %N1. In a step climb at a vertical speed of 1500fpm, it makes no difference, but once on a longer climb, it can be very useful.

All of the above for B738 of varying ages.

After many years of operating the B737, it's never been mentioned that MCT is anything other than a useable, normal, maximum continuous thrust, albeit one that is most often associated with an engine out scenario. If it is considered as strictly an emergency use only, then I'm with Rat5- it's wrongly labelled.

[Derfred]

Note that with U11.0, the limit in cruise reverts to CLB now, not CON.

Not in my airline it doesn't. It reverts to CRZ.

I suspect CLB limit in cruise may be a customer option (or loadable default?).

[ImbracableCrunk]

The FAA's view is "is to always have available the highest thrust
selected by the applicant and certified for continuous unrestricted operation." Also, " The airworthiness requirements do not recognize emergency ratings for fixed-wing
aircraft." These quotes are from a relevant FAA policy statement available here: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/b4c6c780ec6e10e186256bf40070ace1/$FILE/2000-00112.pdf
I saw that FAA letter, too. It's dated 2000. The Boeing Doc is from 2009. I don't know if the Boeing JTPM would (or could) supersede an FAA memo.

[donstim]

I saw that FAA letter, too. It's dated 2000. The Boeing Doc is from 2009. I don't know if the Boeing JTPM would (or could) supersede an FAA memo.
No Boeing document can supercede an FAA memo that is still in effect.

[ImbracableCrunk]

No Boeing document can supercede an FAA memo that is still in effect.

I wouldn't think so, but I wonder where Boeing get their opinion when the FAA memo was out 9ish years prior.

[tdracer]

I've done some work on engine rating developments. In the engine ratings, Max Climb can never be higher than CON - CON occurs at a higher throttle position than max climb and it's a big no-no to the regulations to have thrust drop with increased throttle angle.
Now, there may be cases with a big derate takeoff where the usable CON rating is less than the Max Climb rating, but that'll be due to aircraft handling considerations (e.g. what the FMC displays). For example, it's well known that the 737 has a significant pitch-up characteristic with increasing thrust. In an extreme case, with a lightweight aircraft selecting max rated (CON or TO) thrust at low airspeed could result a greater pitch-up moment than can readily be controlled via the tail. But it you push the throttle to the firewall, you'll get either Max Con or Max Takeoff thrust (depending on the altitude/airspeed).
At least on the aircraft I worked (747-400, 767), Max CON and Max Climb were the same over 30k. So above 30k, there would just be a big 'flat' above the Max Climb TRA.

[barit1]

IC asked this in a PM to me, but there's no reason not to share it with the caveat:
First a caveat: it has been 3+ decades since I worked in flt ops directly, and my experience was mostly on CF6 and bigger engines. However, I doubt if that has any significant effect on this issue.

That said, MCT is a cert limit, whereas MCL (CLB) is imposed by the engine maker as a warranty limit. Thus while running above MCL up to MCT may cause the airline and CFM (the company) to haggle over engine deterioration rate, no laws have been broken.

Note also that for some engine models, some or all of the MCL power management schedule may in fact coincide with MCT. In this case there is no real issue.