It strikes me as surprising that the 737 flight management system doesn't provide a way of knowing how many VNAV constraints you've actually deleted with ALT INT button presses. It's certainly caught me out a few times: pressing the button too frequently over the far side of the cockpit without really paying attention - then wondering why the descent path isn't quite what it should be!

 

Of course, RW pilots (i) are very attentive and (ii) always use progressive MCP altitude settings to ensure they don't bust heights and levels. But is there some kind of check or tell-tale for the number of executed altitude interventions still to have their effect on the active flight plan? Couldn't find any FCOM reference to any such feature.

 

Thanks.

 

David

Typically, one pilot is on the LEGS page, and you monitor the restrictions there.

Thanks.

 

But I wasn't aware that the Legs page tells you whether you've intentionally or unintentionally overridden any particular active altitude constraint by pressing Alt Int. ...

 

David

It doesn't tell you about your intentions. It tells you the restraints.

 

If you have an alt restraint on the legs that you don't want, hit the button. There are no secrets or tricks.

Thanks, Spin.

 

I'm obviously not being clear with my question: is there a way of telling how many altitude constraints you've eliminated by pressing Alt Int successively? Or do you just have to remember - which has been my assumption!

 

Best wishes,

 

David

Thanks, Spin.

 

I'm obviously not being clear with my question: is there a way of telling how many altitude constraints you've eliminated by pressing Alt Int successively? Or do you just have to remember - which has been my assumption!

 

Best wishes,

 

David

 

Not in front of the NGX right now, but shouldn't the constraints disappear from the CDU when you hit ALT INT? In other words, the altitude on the LEGS page should be in small type rather than large type? I suppose you'd have to compare what's currently listed versus the actual chart.

I havent really tried it yet, but isnt the ALT INT button suppose to delete hard constraints between your PRESENT altitutde and the altitude you set in the MCP window? So if the altitude in the MCP window is higher than a constraint, it wouldnt delete that constraint? Or am i thinking of something else?

According to the 737NG FCOM, during a VNAV descent, each push of the ALT INTV switch will delete an FMC altitude constraint. If all FMC altitude constraints are deleted, the descent mode will revert to a VNAV speed descent.

 

Not sure that even this would over-rule an altitude set on the MCP, though.

 

Good questions, David and Bryan.

Yes that exactly right. But when you press Alt Int more than once, it deletes two constraints in a row - as far as I know "invisibly", ie there's nothing to remind you or tell you that you've eliminated an altitude constraint until you sail through it! Not quite a fail safe system apart from only altering MCP altitude step by step ...which was really my question: is there no indication of how many times you have actually pressed Alt Int ...

 

Best wishes,

 

David

Yes that exactly right. But when you press Alt Int more than once, it deletes two constraints in a row - as far as I know "invisibly", ie there's nothing to remind you or tell you that you've eliminated an altitude constraint until you sail through it! Not quite a fail safe system apart from only altering MCP altitude step by step ...which was really my question: is there no indication of how many times you have actually pressed Alt Int ...

 

Best wishes,

 

David

If there are alt constraints, they show on the legs page. That is where you see if you have deleted them, also.

 

Look at the legs page. Big numbers mean you won't sail past your alt, little numbers mean that's where the box approximates you'll cross.

 

Look at the LEGS page.

Hmm, okay, Matt. Thanks. Hadn't taken account of the typographical differences in that way, so I'll take a closer look at this.

 

Best wishes,

 

David

Back up your monitoring of the LEGs page by using the DATA selection on your EFIS Panel...this will present ETA & ALT constraint info (if it exists) for each WPT along track on yr ND.

 

A picture paints as they say & there are plenty aids to help your SA.

 

As you succesively press the ALT INTV button they will dissapear from the ND.