B737 MCP modes operation

[Stamatis]

Hi!

Following question relates to the 737NG.

Suppose you are flying level, in ALT HOLD, HDG mode and A/T SPD mode towards your ILS intercept.

When you get cleared for the ILS approach, you press the APP MCP button.
Question:
Does the APP light come up immediately, and the HDG light extinguishes, or does the HDG light remain ON until Localizer intercept begins?

Same question regarding APP and ALT HOLD, in relation the Glide Slope capture. When does the ALT HOLD light extinguishes? Upon pressing APP or upon capturing the G/S?

I am not referring to the PFD mode annunciators, just the MCP button/lights.

Stamatis

[Portly]

I shall try this out ASAP, but simply put, an MCP annunciator is illuminated to show a mode has been selected and may be de-selected, so if you are flying level to the intercept and you arm APP, then APP becomes selected and may be de-selected until GS intercept, so only after intercept does it become impossible to de-select.

This rule should apply to all other modes, too. To clarify this in your mind, watch the MCP annunciations during a normal take-off and initial climb.

Out of interest, there are hazards lurking in the fact that the MCP can show different annunciations to those on the EADI. Beware.

If you know more than I, please feel free to shoot me down in flames!

[Stamatis]

"If you know more than I, please feel free to shoot me down in flames!"

LOL, if I knew more I wouldn't be asking <g>.
I am not a real-world pilot.

But please clarify:
Are you saying that the APP MCP light will be ON from the instant I press the APP button, and that the HDG MCP light extinguishes at the same time?

If that is the case, I assume that despite the non-lit HDG light, I am still in HDG mode, in conmformity to my PFD mode annunciators, and I can still change my heading via the Heading knob until the A/P starts intercepting the LOC, despite the fact that the HDG light is turned OFF, right?

Also, can you please clarify what you mean when you write:
"then APP becomes selected and may be de-selected until GS intercept, so only after intercept does it become impossible to de-select"

If I want to de-select APP mode after GS intercept, for whatever reason, and there can be many, do I have to turn the A/P OFF? There is no way I can de-select the APP mode?

Stamatis


[This message has been edited by Stamatis (edited 13 September 2000).]

[ManaAdaSystem]

When you get cleared for the ILS approach, you press the APP MCP button.
Question:
Does the APP light come up immediately, and the HDG light extinguishes, or does the HDG light remain ON until Localizer intercept begins?

Same question regarding APP and ALT HOLD, in relation the Glide Slope capture. When does the ALT HOLD light extinguishes? Upon pressing APP or upon capturing the G/S?

The APP light lights up immediately, and HDG light stays on until localizer capture.
The ALT Hold light extinguishes when you capture the G/S.

If you want to deselect APP mode after capture of LOC and G/S youve got three ways of doing that. Pushing APP button will not do the trick, that option is inhibited.
1. Press TOGA switch
2. Disengage autopilot and turn off both flightdirectors
3. Retune (change frequency) a VHF nav receiver.

[Stamatis]

The APP light lights up immediately, and HDG light stays on until localizer capture.
The ALT Hold light extinguishes when you capture the G/S.

I see. So it is possible to have two lateral and two vertical mode lights ON simultaneously. I find this interesting.

I assume then that the same happens when on an intercept to our flight plan "magenta line" while in HDG mode, and engaging LNAV? LNAV light goes ON but the HDG light will once again remain ON until the A/P captures and tracks the magenta line?

Thank you for your reply regarding de-activating the APP mode after capturing the G/S.

Stamatis

[ManaAdaSystem]

I see. So it is possible to have two lateral and two vertical mode lights ON simultaneously. I find this interesting.

Yes, its possible, but the lights only mean that they can be deselected. You always look at the FMA (flight mode annunciations) to see what modes you have.

[Stamatis]

Yes, its possible, but the lights only mean that they can be deselected. You always look at the FMA (flight mode annunciations) to see what modes you have.

Sure, no misunderstandings in this respect.
Thanks for the explanation.

Stamatis

[This message has been edited by Stamatis (edited 16 September 2000).]

[Professional Pilot]

"I assume then that the same happens when on an intercept to our flight plan "magenta line" while in HDG mode, and engaging LNAV? LNAV light goes ON but the HDG light will once again remain ON until the A/P captures and tracks the magenta line?"

If you are on an intercept HDG( within 90 degrees ), and you have sequenced an Intercept TO Leg, by pressing LNAV the light on MCP will illuminate and the FMA will annunciate L NAV in green and the HDG mode and light will extinguish.

[Stamatis]

and you have sequenced an Intercept TO Leg

Care to please explain what you mean by "sequenced"?


[This message has been edited by Stamatis (edited 16 September 2000).]

[Professional Pilot]

Omit that word with the rest of the sentence remaining the same. Do you still get the point.

[Stamatis]

Omit that word with the rest of the sentence remaining the same. Do you still get the point.

Yes I do, thank you. However, I would like to know what would be the status of the MCP lights, if I am not on my FMC route, I fly in HDG mode towards the route (with an intercept course of less than 90 deg) and I push the LNAV button. Will both the LNAV and the HDG light stay ON till the route is inttercepted?
No extra "Intercept" legs programmed, just the original route.

[Phoenix_X]

I think (and another 737 pilot here with me) that as soon as you push the LNAV button to intercept the track the HDG Select button will extuingish and LNAV will illuminate. The FMA will immediately annunciate LNAV as well, even when still intercepting the track. You can no longer change heading by moving the bug at this point.

If I have a chance to check this in the near future I will.

[Stamatis]

I think (and another 737 pilot here with me) that as soon as you push the LNAV button to intercept the track the HDG Select button will extuingish and LNAV will illuminate. If I have a chance to check this in the near future I will.

So the behaviour is different than when intercepting a LOC under HDG and engaging the APP button. In the LNAV case, the HDG light goes off immediately, while in the APP case it goes off only when the LOC is intercepted. I hate these inconsistencies :-)

Stamatis

[This message has been edited by Stamatis (edited 18 September 2000).]

[dununder_upover]

Just a thought from an old clockwinder

In order to not have heading mode with an ILS mode you must first capture the ILS (LOC)same is true for V/S mode you must first capture G/S.

Alternativley if you are in HDG mode and select LNAV there is no delay as the flt plan can be adopted immediately, ie there are no external radio signals to intercept and track. So the HDG light go off immediately.

[skynet737]

Stamatis

ok here goes....

"Suppose you are flying level, in ALT HOLD, HDG mode and A/T SPD mode towards your ILS intercept. When you get cleared for the ILS approach, you press the APP MCP button.
Question 1:
"Does the APP light come up immediately, and the HDG light extinguishes, or does the HDG light remain ON until Localizer intercept begins?"
Answer 1. the APP light comes up immediately AND the HDG light remains ON till LOC capture.

Questin 2.

"Same question regarding APP and ALT HOLD, in relation the Glide Slope capture. When does the ALT HOLD light extinguishes? Upon pressing APP or upon capturing the G/S?"

Answer 2. The ALT HOLD light would have extinguished when you acquired your altitude ie., when you levelled off 'at your MCP Selected Altitude'. this could be your glide slope intercept altitude.
the logic for the lights is that a light on the MCP illuminates for a ARMED mode (in this case APP) as well as for an engaged mode(eg., HDG) except once engaged in certain modes the light may be extinguished to indicate the mode cannot be deselected.
hope this helps.... :)

[Stamatis]

the logic for the lights is that a light on the MCP illuminates for a ARMED mode (in this case APP) as well as for an engaged mode(eg., HDG) except once engaged in certain modes the light may be extinguished to indicate the mode cannot be deselected.
hope this helps....

Of course it helps, thank you.
But your above stated logic does not hold true in the example of HDG and LNAV, according to the replies I received above.

[skynet737]

"Of course it helps, thank you.
But your above stated logic does not hold true in the example of HDG and LNAV, according to the replies I received above."

"I assume then that the same happens when on an intercept to our flight plan "magenta line" while in HDG mode, and engaging LNAV? LNAV light goes ON but the HDG light will once again remain ON until the A/P captures and tracks the magenta line?"

nope.... the replies to your querry r all correct... the LNAV light comes on immediately and LNAV would annunciate on the FMA as engaged (provided LNAV capture critera was met when you pressed LNAV)... the HDG light would immediately extinguish... and the HDG annunciation would go(replaced by LNAV)

"the logic for the lights is that a light on the MCP illuminates for a ARMED mode (in this case APP) as well as for an engaged mode(eg., HDG) except once engaged in certain modes the light may be extinguished to indicate the mode cannot be deselected.
hope this helps...."

the logic hold even in the LNAV and HDG case because LNAV does not have a 'armed' mode....hence it only 'engages' when selected and capture criteria are met.

its all a little confusing if you havent actually used it... then its a cake... :)

[747400CA]

"You always look at the FMA (flight mode annunciations) to see what modes you have."

Heard a good one a while back that seems to sum up this topic nicely:

Instructor (pointing first to MCP and then to the FMA in the simulator)

"THIS [MCP] is rumour, but THAT [FMA] is FACT"

Thanks to all.