B737 SP-77 Autopilot Interface

[sparkfarmer]

Hope someone can help!

We are an approved TC Aircraft Engineering Organization and,

I am installing a new Flight Management System in an older Boeing B737-200 jetliner. The 737 uses the Honeywell SP-77 autopilot. The SP-77 autopilot was fairly advanced for its day in that it calculated roll rate corrections based on aircraft speed.

My problem:
The new Flight Management System (FMS)also calculates roll rate corrections based on aircraft speed, so if I feed the roll steering output of the FMS into the autopilot (SP-77) without any other changes, then both units will apply a correction for speed, and the aircraft will turn too slowly and miss it's intended track.
How do I disable the Q-pot portion of the SP-77 input so that the SP-77 will ignore it's internal speed programming.

 

[Barry1961]

http://www.eng-tips.com/threadminder.cfm?pid=16

The Areonautic forum would probably be a better place for your post.

Barry1961

 

[blackwed]

And as the 737 that's supposed to take me to Philly tomorrow rotates with about 3,000 feet remaining on 33, am I to feel good knowing that she may have been serviced based on info the mechanic obtained from the web?

DB

deja moo: I've heard that BS before.

 

[sparkfarmer]

Barrie: Thanks, I will move it to Aeronautics. (Still new at this and didn't know where it would fit best).

blackwed: Don't worry, everything that is received as advice has to be thoroughly sanity checked. The question isn't as scary as it sounds. The problem is the age of the system (SP-77) - it's getting difficult to get advice on how to do certain things.

 

[blackwed]

Sparky, I couldn't resist. My wife and I are taking a trip with another couple tomorrow and I've spent weeks trying to convince both ladies of how safe air travel is. They both have to get all medicated when they fly and still every time we hit a pot hole, it takes their breath away. You can watch the blood return to their faces when we touchdown.

DB

deja moo: I've heard that BS before.

 

[sparkfarmer]

No problem blackwed. Just before touchdown turn to the other couple, smile, and say "I bet you a dollar he bounces this thing".