After successfully climbing to my desired altitude (ASEL) in the CLB thrust mode, I level off as expected. However, once levelled off, I notice I'm unable to maintain that altitude as very slowly the aircraft starts to sink. Nothing dramatic, maybe 100 ft/min or less. After a while, the alarm will sound indicating 1000' from selected altitude. Flying above FL180, I do have my altimeter set to standard pressure.

 

Does anyone have an explanation why this is happening, and what I can do to prevent it? What is the best way to to recover ... I have not figured out if using ASEL, or VS to get back up to altitude is the correct option. Sometimes one works, sometimes the other.

 

Happy holidays.

Since you did not mention it, I have to ask....is the auto pilot engaged?

 

Jim

So the 1000ft alarm is going off twice?

 

Ex: you have 10,000ft set in the autopilot, you reach 9000 and the alarm goes off, you level off, sink, alarm sounds again?

 

and this happens with AP on, ASEL selected, no Vnav selected?

 

-Are you useing the FMC? - Correctly?