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B737NG select left or right RA for Dual Channel Approach?

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B737NG select left or right RA for Dual Channel Approach?

Old 15th Sep 2021, 11:45
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Join Date: Aug 2005
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B737NG select left or right RA for Dual Channel Approach?

hi all,

In a B737 is it possible to select left or right radio altimeter for a ILS Dual Channel Approach?

Are these the correct sequences:

for F/O:

F/D right, CMD B and finally CMD A after APP came alive. Would this provide the F/O to commence a Dual channel approach from the right side with RA right?

for CMD:

F/D left, CMD B and finally CMD A after APP came alive. The one for the CMD Side?

History of this options?
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Old 17th Sep 2021, 09:29
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Specification of this question:

It refers to Boeing's FCOM Automatic Flight Chapter 4 System Description Section 20 (4.20.3)Flight Director Display

Turning a F/D switch ON displays command bars on the respective pilot’s attitude indicator if command pitch and roll modes are engaged. If command pitch and roll modes are not engaged, the F/D command bars do not appear. The F/Ds can be operated with or without the A/P and A/T. F/D command modes can be used with an A/P engaged in CWS. F/D commands operate in the same command modes as the A/P except:
• the takeoff mode is a F/D only mode
• dual F/D guidance is available for single engine operation
• the F/D has no landing flare capability. F/D command bars retract from

view at approximately 50 feet RA on an ILS approach. Normally, FCC A drives the captain’s command bars and FCC B drives the first officer’s command bars. With both F/D switches ON, the logic for both pilots’ F/D modes is controlled by the master FCC, and both FMA displays show the same mode status. The master FCC is indicated by illumination of the respective master (MA) F/D indicator light. The master FCC is determined as follows:
• with neither A/P engaged in CMD, the FCC for the first F/D turned on is the master
with one or both A/Ps engaged in CMD, the FCC for the first A/P in CMD is the master FCC, regardless of which F/D is turned on first.

Does the sequence of activation of CMD A and B comply with the description in this chapter?
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