737 NG EEC alternate

[framer]

Hi,
The QRH states:
2 Thrust levers (both) . . . . . Retard to mid position

This prevents exceeding thrust limits when switching to the EEC alternate mode.


In my mind the thrust levers are already in a 'mid position' when cruising with 88% N1 set. I imagine it provides sufficient buffer to limits and would consider that step satisfied.
Your thoughts?

[tdracer]

2 Thrust levers (both) . . . . . Retard to mid position

Selecting Alternate mode can occur pretty much anytime during the flight, so the throttles could potentially be anywhere from idle to max climb. Since selecting alternate mode off idle will nearly always result in an increase in N1 - potentially quite sizable - it's a standard instruction to set the throttles to a 'mid' position before selecting Alternate (those words appear for all current production Boeing aircraft).

Obviously, if the throttles are already 'mid' position or lower, there would be no need to retard them.

[framer]

Thanks td.
I understand that. To be more specific with my question, do you think that 88%N1 ( ie a standard cruise setting) is 'mid' enough to prevent any excedance being possible.
Personally I do, but I know of others who would retard the levers further in order to achieve a 'mid' position.
Cheers

[Emel.OW]

By the way, how can you notice EEC Altn light during routine operations? As far as I remember it doesn't trigger master caution, so if there's no DEU failure with DSPLY SOURCE annunciation you'll hardly ever see it.

[tdracer]

Framer, I don't work 737 (I'm a wide body sort of guy :E), so I can't really comment on the specifics of the 737 installations. Your answer would probably have to do with the exact cruise conditions and how close you already were to max climb/con power set. But I suspect it is a least possible to exceed the max climb/con rating by selecting alternate mode with the throttle at a 'normal' cruise setting.

[framer]

Thanks again.
But I suspect it is a least possible to exceed the max climb/con rating by selecting alternate mode with the throttle at a 'normal' cruise setting.
That really is the crux of the matter in that some people do suspect that, and others ( like myself )don't think it's likely there will be a 11 or 12% increase in N1. Unless I get more info I will be conservative and assume that it is possible as there is nothing to lose by retarding the levers a bit more.
I'm a wide body sort of guy
Don't feel bad. I used to have the same problem until I entered a workplace 'Biggest Loser' competition. I now have so much energy it's amazing.
By the way, how can you notice EEC Altn light during routine operations?
You do get ENG on the master caution panel.

[RAT 5]

I'd always thought 'mid-position' was physical geometric thing rather than an N1%. Wrong or right?

[MrHorgy]

RAT 5,

I don't think so, as the thrust levers aren't linearly(?) aligned with the N1, if that makes sense.

[framer]

I think you are right Rat 5 but obviously the reason behind the physical mid point is to reduce the actual engine parameters in case the new data base sourced N1 is significantly higher. ( unless I'm completely missing something......it wouldn't be the first time :) )

[tdracer]

Yes, 'mid position' is geometric, but those instructions are common across the current production Boeing fleet - which encompasses a number of both N1 and EPR engines.
So 'mid position' keeps it simple and common.

[latetonite]

Just imagine a 'Display Source' indication on your PFD, in Climb..and follow the QRH, on your next flight. This will answer the question.

[Igrish 747]

When dispatching with EEC in ALTRN, we should adjust speed.
Why ??

[tdracer]

Could you be more specific - which speed(s) are you speaking of? And are we still talking 737NG?
I know the EPR engine aircraft typically have a weight penalty associated with Alternate Mode dispatch (due to increased uncertainty in thrust) but I don't recall that being extended to engines with N1 thrust settings (GE/CFM).

[FlyingStone]

With hard alternate mode (as in EEC ALTN dispatch), the thrust may be higher than the one in normal mode, resulting Vmc(a/g) will be higher and speeds need to be adjusted.

[Capt Pit Bull]

By the way, how can you notice EEC Altn light during routine operations? As far as I remember it doesn't trigger master caution, so if there's no DEU failure with DSPLY SOURCE annunciation you'll hardly ever see it.


EEC alternate light triggers master caution and ENG on the system annunciator panel.