VNAV engine out cruise drift down

[Hardy Heinlin]

Good evening,

does anybody know -- from sim training -- how to correctly switch from ALL ENG CRZ mode to E/O D/D mode while VNAV is engaged?

In my current model I'm having a cosmetical problem. I proceed like this:

1. I'm at FL370 with ACT ECON CRZ
2. Engine failure occurs, airspeed slowly decreases
3. Push ENG OUT key, get MOD E/O D/D and CRZ ALT auto-set to FL308 (max e/o)
4. I turn MCP ALT down to 30000 and "30000" is in scratchpad

And then comes the problem:


Option A:

5. I push the round MCP ALT knob
6. Aircraft starts descending to FL300 at ALL ENG ECON speed
7. I push EXEC, get ACT E/O D/D and speed reduces to E/O speed

This procedure doesn't look elegant. Two different control tools which are normally isolated from each other -- FMC and MCP -- get intermixed. I turn down the MCP ALT while the EXEC light is on, then push the MCP knob, then the EXEC knob. Slightly chaotic, isn't it? Anyway, I have to push the ENG OUT key to see the MOD E/O page with the suggested E/O altitudes. Only then can I chose a new MCP ALT.


Option B:

5. I push EXEC and get ACT E/O D/D
6. Aircraft starts descending to FL308 and reduces to E/O speed
7. "30000" is still in scratchpad

Now I can remove the "30000" in each CDU with the DELETE key, or I remove it by pushing the MCP knob which will change the CRZ ALT from 308 to 300. This procedure doesn't look elegant either. And it's still a mix of FMC world and MCP world acting within the same process.

...

Also, I wonder if the FMC message "LIM ALT FL308" should appear when I'm above the max E/O cruise altitude and have started the D/D. Perhaps it should be inhibited during the D/D.


You probably won't find the answer in your manuals. But perhaps you did this stuff in one of your last sim checks :-)


Cheers,

|-|ardy

[Mariano]

Hardy,

Not for a 744 but this comes straight from the Emirates 777 SOP Guide and Training Manual under the "Engine Failure or Fire at Cruise Altitude" section.

"ENGINE OUT DRIFT DOWN PROCEDURE" (PF)
Select FMS CRUISE page (PM)
ENGINE OUT (PM)
Select a lower altitude on the MCP (Do Not Push) (PM)
Execute (PM)
Ensure VNAV Engaged (PF+PM)
"MAYDAY,MAYDAY, MAYDAY" Turn on all exterior lights (PM)
"ENGINE FAILURE L/R CHECKLIST" (PF)
Complete the Checklist Items (PM)
"ENGINE FAILURE CHECKLIST COMPLETE" (PM)
"REVIEW EICAS" (PF)
Read all EICAS messages (PM)
Call for any further checklists if required (PF)
"CANCEL EICAS" (PF)
Cancel EICAS (PM)
"CLEAR CHECKLISTS" (PF)
Clear Checklist (PM)

Hope this helps a little,

Mariano

[IefCooreman]

Hmmm... easier when you're "in the situation".

From memory, and not considering the necessity to go off the airway/track:
Select VNAV eng out page (push LSK)
Look at max engine out FL and determine appropriate target driftdown FL (ie in NAT tracks 500ft above/below a regulatory FL)
Set chosen FL in MCP
Push Execute on FMC

You never push the MCP alt button because this forces a cruise descent, not a drift down. In some situations, once you are established on an offset track you do go out of VNAV because the rules of the area you fly in require you to go down to your chosen engine out FL as quickly as possible.

[Hardy Heinlin]

Thanks guys.

So it's option B: I'll have to clear the altitude in the scratchpad with the DEL key.

Or maybe the MCP altitude won't go into the scratchpad when the E/O page is displayed. There are a number of conditions that prevent this scratchpad transfer. The E/O page selection may be one of those conditions.

Generally, the MCP altitude is transferred to the scratchpad when it's above the CRZ ALT in CLB mode, or above/below CRZ ALT in CRZ mode.

...

Another thought:

You can select the exact target altitude with the MCP, e.g a rounded FL310, while the FMC has an odd value like FL307. The aircraft drifts down. A long way to go at -100 fpm or so. Enough time to set the exact altitude in the FMC as well: The scratchpad still has 31000, just push the MCP knob. I think this push won't change the D/D mode to CRZ DES mode once the E/O mode is executed; it probably changes to CRZ DES only if ALL ENG CRZ is active.


Cheers,

|-|ardy

[IefCooreman]

I forgot the step 'set target FL in FMC', after you set it on the MCP an before you press the execute button. How you do it is up to you, so no idea if it would show up on the fmc after being set on the mcp. If it does, you can use it. Otherwise you just type it :-).

Can't help with the mcp alt selector push for the 747 then. We don't use it because it starts a descent, while a driftdown procedure is initially a slowing down in level flight with engines at MCT. Only when you've slowed down to engine out drift down speed (and this can take a long time) VNAV should start the descent.

BTW: nothing prevents you from choosing another speed as well. If terrain and traffic is not a factor, and you have an engine fire, you can choose higher speeds. It's better to do this before you execute the engine out page, because your target FL will be lower with higher speed.

[Richard McDonald Woods]

H,
I don't know that this contains your answers, but might be worth a glance at http://www.airliners.net/aviation-forums/tech_ops/read.main/164288

[Richard McDonald Woods]

Also found this on page 11.31.32 at http://www.smartcockpit.com/aircraft-ressources/Flight_Management_and_Navigation_%28B747-400%29.html

[Mariano]

Hardy,

Just looked at the 744 FCTM. I think your answer can be found in: 4 Climb, Cruise, Descent and Holding > Cruise > Engine Inoperative Cruise/Driftdown section.

If you need me to type this section here, please let me know. Short on time right now.

Thanks,

Mariano

[Hardy Heinlin]

Got it. Thanks!


|-|