Re: Confusion over 777 variants.

Date:         25 Nov 97 03:26:06 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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>> United wanted greater range, so their launch order was for 525,000
>> lbs MGTOW; they were delivered at 535,000 lbs and have since been
>> upgraded to the full 545,000 lbs.

>How did they upgrade those birds ?? The 777-200nonIGW has engines rated
>between 74,000 and 77,000 lbs thrust. As you stated above the MGTOW also
>changes. I was told that those changes can be made by simple
>reprogramming of the FMS software (for the MGTOW) and the FADEC (for
>the engines).

Despite many published statements that United's non-IGW 777-200s have
PW4077 engines, they actually have PW4084 engines that are derated to
77,000 lbs thrust.  (Anyone wishing to argue otherwise should first
check the dataplate on one of them.)  So, they could have increased
the thrust by a FADEC change, though to my knowledge they did not.
(The PW4090 engines on United's 777-222IGWs are different, so they
could not similarly upgrade a PW4084 to a PW4090.)

Aircraft built for higher weights can have their MGTOW upgraded with
a simple FMS change and appropriate paperwork (including payment to
Boeing), but United's 777s include some of the first ones off the
production line.  It's possible that structural modifications were
required before they could be upgraded to the higher MGTOW.  It's
also possible that with continued stress testing, Boeing found that
the basic design was stronger than they thought, in which case it
might have been a simple FMS and paperwork change.

>Are there *really* no other differences between the various
>777-200nonIGW models?

I don't know about the non-IGW, but for the IGW, I'm told there's no
structural difference between the lowest weight IGW and the highest,
assuming you're comparing planes with engines from the same
manufacturer.

>The differences between 777-200nonIGW and 777-200IGW are (in addition
>to FADEC and FMS software), stronger structures and the center tank,
>making it impossible to convert a nonIGW to an IGW 777. Correct ?

There are also some changes in the avionics and maintenance computers
and probably other details, and different engines (not just FADEC
programming), but you're essentially correct.

--
Karl Swartz	|Home	kls@chicago.com
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