737 descend before reaching T/D and mid-flight

[Andrea1 6]

"Real pilot would disco(nnect) the autopilot….."

Why should they disconnect the a/p?

If I was ordered to descent from FL390 to FL370 I would simply use V/S (vertical speed) mode by setting -1000 ft per minute descent rate (by keeping the A/P on)...why make things complicated when the solution is easier?

And if I think that I'll will have to mantain FL370 for a while I'll adjust the new "cruise level" into my CRUISE PAGE of my CDU and, of course reset also 37000 ft into my overhead pressurization cruise altitude window…

Best Regards

Andrea Buono

[Flexman 30]

All you have to do is select the new altitude on the MCP Altitude Window and hit ALT INTV. The airplane will descend on VNAV PTH at a fixed rate of 1000fpm. If you plan to stay long enough at that new altitude, just set up a new CRZ ALT in the CRZ page and change the FLT ALT on the presurization panel. If that's not a new cruise level and you expect to continue descending, when they give you a new cleared level, just set it in the MCP, the airplane will catch the new VNAV PTH and fly it.
Sometimes the instruction is "descend now" and some other times it's "descent at discretion". In one case, you don't have to start your descent until you hit your TOD. In the other case, ATC expect you to descend with at least 500fpm.

[MeatServo 10]

 

On 12/25/2018 at 4:59 PM, vadriver said:

not the first choice near "coffin corner"... the OP's scenario.

Even at max altitude you have a fairly decent range of speed and maneuver margin. I've had to hand bomb it from cruise a few times due to failures causing us to be non-rvsm. 

 

[Spin737 102]

On 12/25/2018 at 4:59 PM, vadriver said:

not the first choice near "coffin corner"... the OP's scenario.

I think it was a joke. Hence the laugh emoji.

[Ephedrin 418]

1 hour ago, Spin737 said:

I think it was a joke. Hence the laugh emoji.

Knowing his faible for the 707 and shooting the IGS13 into kai tak manually with raw data it definitely was one 😄 

[KaptainKaos 0]

I'm not sure if it's the proper procedure, but what I do is dial in the new alt on the MCP, then change the cruise alt in the FMC.
Once in a while the airplane will not seem to respond. If/when that happens I'll just click the VNAV button on the MCP off then on again.
That seems to wake it up.

If ATC has instructed me to 'descend via the XXXXX approach' (STAR) I'll select one of the waypoints where the alt restriction is in the 4-7,000' range AGL (for example 6,000' on app to KLAX would be equivalent to 11,000' on app to KDEN). I'll set the MCP to that alt. I like to start my descent 10-15nm before I reach the calculated TOD in the FMC, especially if I have a healthy tailwind.