Speed intervention while descending?

[stolowski]

Hi,

I'm not sure if I'm doing something wrong, or this is a bug, but... I'm flying with AP, VNAV and LNAV active (following FMC flightplan), just passed T/D and the plane started descending.

Now, I'm trying to reduce the speed via MCP: the IAS/MACH display is blank, so I hit SPEED button on the MCP, the MCP SPD is announced on the PFD, but the IAS/MACH remains blank and I still cannot dial in the desired speed... Is this by design? 

Edited June 13, 2016 by stolowski
added screenshots

[Nils]

Hi, I'd say part bug, part design. Pressing SPEED in this situation shouldn't do anything so that's a glitch (we never thought of trying it). We'll patch that up right away.

Regarding your speed situation, the engines are at idle so the only thing you can do to slow down is to 1) extend speedbrakes and 2) level off by selecting LVL CHG and dialing in a lower speed which will make the aircraft pitch up.

[stolowski]

This makes sense... Thanks for the explanation and quick reply!

One more thing - only now I noticed that the small display of the current flight phase (does it have a name?) located below LVL CHG and HDG SEL MCP buttons and engine instruments gauges shows 'CLB' while the aircraft is already descending and a moment ago (I'm still in this flight while typing this and still descending) it turned into CRZ, so possibly another small glitch.

Edited June 13, 2016 by stolowski

[dornier]

Just out of curiosity, does the 737-300 allow for speed intervention while in VNAV during a descent or non-ILS approach?

Thanks,

George

[Litjan]

4 hours ago, stolowski said:

This makes sense... Thanks for the explanation and quick reply!

One more thing - only now I noticed that the small display of the current flight phase (does it have a name?) located below LVL CHG and HDG SEL MCP buttons and engine instruments gauges shows 'CLB' while the aircraft is already descending and a moment ago (I'm still in this flight while typing this and still descending) it turned into CRZ, so possibly another small glitch.

Not a glitch - this is the N1 limit indicator and not the flight-phase indicator. It shows what maximum power the engines COULD go if needed.

1 hour ago, dornier said:

Just out of curiosity, does the 737-300 allow for speed intervention while in VNAV during a descent or non-ILS approach?

Thanks,

George

Not this model. The SPD INTV and ALT INTV are features that are not available on all Classics, and we chose to omit them to keep things a bit simpler.

Jan

 

[dornier]

7 minutes ago, Litjan said:

Hi Jan,

Thanks for the info.

George

>>Not this model. The SPD INTV and ALT INTV are features that are not available on all Classics, and we chose to omit them to keep things a bit simpler.

Jan

 

 

[stolowski]

8 hours ago, Litjan said:

Not a glitch - this is the N1 limit indicator and not the flight-phase indicator. It shows what maximum power the engines COULD go if needed.

Not this model. The SPD INTV and ALT INTV are features that are not available on all Classics, and we chose to omit them to keep things a bit simpler.

Jan

 

I see, thanks for the explanation!