B737 Takeoff with VNAV and LNAV disarmed

[poldek77]

Originally Posted by Tomaski

Wait.... what?? You can actually takeoff with the LNAV and VNAV disarmed?!

Yes, I can.

LNAV - normally armed on the ground but I have flown some SIDs where it's not possible due to location of the 1st waypoint. According to OM-B:
Note: For LNAV to be armed on the ground, the departure runway must be selected and the course, to the first waypoint, must be within 5 degrees of the runway heading.

VNAV - my company allowed us to arm VNAV on the ground just last year so before that we used it after clean up. Nowadays armed for take-offs except noise abatement departures - some pilots prefer FLCH, others - VNAV+SPD INTV. On PF's discretion.

[N1EPR]

Its been a few years since I retired, but the B757s I flew tracked runway centerline after TO unless something else was selected. This makes a lot of sense since the protected airspace in case of engine failure is along centerline.

[Airone2977]

Originally Posted by poldek77

Yes, I can.

LNAV - normally armed on the ground but I have flown some SIDs where it's not possible due to location of the 1st waypoint. According to OM-B:
Note: For LNAV to be armed on the ground, the departure runway must be selected and the course, to the first waypoint, must be within 5 degrees of the runway heading.

VNAV - my company allowed us to arm VNAV on the ground just last year so before that we used it after clean up. Nowadays armed for take-offs except noise abatement departures - some pilots prefer FLCH, others - VNAV+SPD INTV. On PF's discretion.

When selected on the ground, LNAV engage at 50ft, VNAV at 400ft.
The issue with VNAV armed on the ground is in the case of engine failure after V1. If you didn't carrefully select EO acc Alt on Take off page 2, it will level off and accelerate to VREF40 + 70 at 1000ft AGL. It could be hazardous expecially if you have high terrain in the vicinity

[Tomaski]

Originally Posted by Airone2977

When selected on the ground, LNAV engage at 50ft, VNAV at 400ft.
The issue with VNAV armed on the ground is in the case of engine failure after V1. If you didn't carrefully select EO acc Alt on Take off page 2, it will level off and accelerate to VREF40 + 70 at 1000ft AGL. It could be hazardous expecially if you have high terrain in the vicinity

Just a minor, though pertinent observation here. The 'it' you refer to above is the automation (either Flight Director or Autopilot). At my airline, our practice is to not engage the A/P in an engine out situation until the flaps are retracted, but this might be different elsewhere. That being said, the aircraft should not level off unless the flying pilot wants it to level off, which speaks to the issue of automation dependency. One of the biggest challenges of modern airliners is to know when to override what the automation is trying to do. Yes, ideally one should set the AFDS panel correctly, but if this was not done or done incorrectly, then the pilot needs to be able to fly with reference to the attitude indicator and not the FD bars.