73NG FMC fix radius

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23rd February 2019 | 06:20

#1 (permalink)

galdian

Thread Starter

Joined: Dec 2006

Posts: 922

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From: australia

73NG FMC fix radius

Hi all

Just curious - and maybe common to all FMC's - the fix page will accept xxx/511 but will not accept xxx/512.
Any reason why 512nm is the magic cut off point??

Cheers.

23rd February 2019 | 08:14

#2 (permalink)

AviatoR21

Joined: Jun 2006

Posts: 201

Likes: 53

From: FLXXX

The Airbus A320 only accepts up to 256NM fixes as this is all the spare memory it has 256Kb. Lucky for you the Boeing has double - 512Kb. No, this is not a joke!

23rd February 2019 | 09:55

#3 (permalink)

Chesty Morgan

Gender Faculty Specialist

Joined: Mar 2002

Aviation Qualifications: ATPL

Posts: 2,325

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From: In your head.

512 bits (computery things) where 0 is the 1st and 511 being the 512th.

23rd February 2019 | 14:59

#4 (permalink)

fox niner

Joined: Jul 2004

Posts: 751

Likes: 72

From: Netherlands

If you write 511 in binary, it is 11111111. (8 digits) for 512, you write 100000000, which is 9 digits. The fmc is an 8-bits computer, which can not handle 9 digit binary numbers.
Apparently this is the case if you have a single fmc configuration in your 737. With a dual fmc, things might be different.
The 8 bits config was chosen because of cpu stability.