Stupid question why LVL Change in a SE situation

[Pin Head]

Hi

Stupid question but why do we do LVL CHANGE when at UP speed normally.

The SPD window is open so you can set your target speed there. AT is disengaged so out of the equation,

Thank you

Pin

[Skyjob]

To get valid FD PITCH commands for FULL THRUST on the operative engine.

Other modes for this situation would only include V/S, which should never be used in SEO, as you are in control of thrust levers and will only be chasing FD's. Keeping the modes used simple and manipulating manually the thrust levers appropriately is the trick to very stable SEO.

[gearpins]

To get the best performance out of the aircraft in the given situation.
One engine at Max thrust, accelerate to UP speed ( best L/D ) maintain UP speed and transition from level accelerating to climb using LVL CHG.
once trajectory established reduce to CON thrust.
:)

[Pin Head]

So vertical FD guidance goes from Toga to MCP SPD.

Yes makes sense just thought that at up SPD it would give same FD command demands.

[TypeIV]

I think that the TOGA and MCP-SPD aren't identical pitch modes.

TOGA won't allow the airplane to sink to gain speed which MCP SPD will, hence the need to wait a couple of segments before going MCP SPD since you have only 35' of terrain net path terrain clearence.

[de facto]

Pin head
Remind us how many hours on type do you have?was it 10000 +?,about to upgrade a few months back if i recall.
How did it go?got messed up with your pitch modes?:D

[Pin Head]

oh de facto you still make me laugh!

There is no stupid question in aviation.

:D:D:D:D:D:D:D:D:D:D:D:D:D:D:

[Denti]

Again it seems that the relevant mode might depend on company SOP and equipment status. If one arms VNAV before takeoff it takes care of everything in the single engine case. It schedules the acceleration at the correct height and then climbs at the flap manouvering speed again once the airplane is clean. No level change needed, no mode change needed either.

[framer]

What aircraft type?

[Pin Head]

hi

thanks for responses.

NG

[ImbracableCrunk]

What aircraft type?
I would assume 737. How many other planes have LVL CHG?

[framer]

No idea, how many? All of the Boeings or just one? I'm only type rated on the 737-300's and NG's so have had limited exposure to the others.

[underfire]

Accident report on LVL CHG

https://www.atsb.gov.au/media/5304685/AO-2104-179%20Final.docx

[Piltdown Man]

Am I missing something? This report implies that LVL CHG was the problem. I disagree, it was failing to notice that an inappropriate Mach value was selected by the aircraft on conversion. Exactly the same effect could be achieved by entering rubbish numbers in the FMS and letting VNAV do the flying. LVL CHG is an excellent mode if the speed selected is sensible. I agree with the outcome of the report, but I do not agree with its sentiment. It was nothing to do with managing a highly automated aircraft, it was the crew not noticing that an inappropriate speed had been selected in a very basic A/P mode.

Returning to the OP's initial question, I believe that an SOP restricting crews to using LVL CHG when single engine is a very crude but effective way of simplifying flight. , The Flight Director will always give valid pitch cues (speed control by elevator) when changing level, no matter what thrust setting is used - thus making your life a little easier.

PM

[RAT 5]

The Flight Director will always give valid pitch cues (speed control by elevator) when changing level, no matter what thrust setting is used - thus making your life a little easier.
Are you sure? I've seen many a cadet in the sim select a change of MCP altitude but not set an appropriate thrust. As you say the FD is in Speed mode for pitch and if there is no thrust increase in level flight it will stay level to maintain the speed. Or am I missing your true meaning?

[Piltdown Man]

I totally agree. The aircraft will do that when Bloggs selects a new altitude, presses LVL CHG but keeps the thrust constant. But if he increases thrust and it will climb. Reduce it and it descends; all at the selected speed. But by keeping to very simple modes (three modes - ALT, acquire [or whatever yours is called] and LVL CHG) you simplify the flying. As to whether or not this is a good thing is questionable, but it is very simple and keeps surprises to the minimum.

PM

[Pin Head]

Good stuff guys.

This is why I asked the question. I think that defacto should resign with immediate effect for critising me for the asking the question in the first place.

[RVF750]

No, taking the mickey is part of life on here. Putting too many "the" into your post is unforgivable though....:rolleyes: For my 2p worth, LVL CHG is crude but effective when dumbing down is the raison d'etre for the S.O.P.

[Being738]

LVL CHG "burn" pchinetich energy isnt that effective at lower alt