Vnav does not engage on the ground B737NG
 

Hello,

Has anyone came across the issue where VNAV cannot be selected on the ground, and only when airborne above 1000AGL?
I thought there was a service bulletin on it, but its referring to Update 10.7.

The aircraft from what I have been told has Update 12.0 installed. LNAV also drops out on the take off roll but can be reengaged.

I dont have access to MyBoeing Fleet personally, but if anyone could shed some light on the subject or the bulletin (if there is one) number that would be great.

Cheers.

Are yo usure the correct hardware is installed as well on this aircraft?

Requirements VNAV armed for takeoff:

• Valid flight plan (beware of an off centre runway alignment, if need be execute direct first waypoint)
• Performance data entered and executed (may need to reengage VNAV after an update to this)
• Both flight directors ON
• Hardware requirements:
  • Rockwell Collins P4 FCC or later
  • or Honeywell -710 FCC or later
  • and CDS BP06 software installed

If an older version of FCC or CDS software is installed VNAV will not engage or arm on ground.

Ive passed on the information Skyjob thank you. I am curious about the fault myself. The issue seems to be on the Primera B737NG, so far two aircraft have been written up with the issue, the common denominator is the Captain.

Care needs to be taken when using VNAV for departures, as default values are used on TAKEOFF PAGE 2/2 and these may need adjusting, depending on departure profile NADP1 or NADP2 or a non-standard use of either (eg using 1500' instead of 1000' flap retraction altitude):

• thrust reduction height
• acceleration height

Both references are used as AGL, not altimeter.
Thus an airline changing over to these automated profile MUST ENSURE the heights are made available to crew, rather then the MFRA as an altimeter altitude only as likely was previously used by its crew.
If airline is using OPT a config setting can be adjusted to display both MFRA and MFRH (MFRH in lower smaller letters displayed underneath or next to MFRA to be set by crew on altimeter tape bug), this is a to do item for the EFB Admin team of the airline. The MFRH is then used by crew and entered into TAKEOFF PAGE 2/2 as ACCEL HT.