View Full Version : 737-800 AC pack inop procedure
23rd Jun 2012, 00:55
Right AC pack inoperative today. The DDPG told us to apply the following procedure: When dispatching with a single pack on for takeoff (airplane pressurized), V1 (MCG) should be determined based on AC packs OFF. Takeoff performance should be based on AC packs ON/AUTO.
I know that V1 MCG is rarely limiting on the 737 with a dry runway, but I've never seen a correction table to adjust your V1 for AC packs OFF. The Captain did not know either. Anyone else? I've been looking through our Performance preamble, FCOM and QRH and cannot find anything about it.
23rd Jun 2012, 07:17
Under V1 (MCG) table in Performance Inflight section says (Classic): For A/C OFF increase V1 (MCG) by 2 knots.
So, if the DDPG requires you to adjust V1 (MCG) for A/C OFF, you just increase the V1 (MCG) by 2 knots and then see if it requires raising your actual V1 (most probably not).
Been around for as long as I can recall, but never known to have an effect on actual V1 as FS says.
23rd Jun 2012, 07:34
hello 172 driver, you correct the V1mcg, not the normal V1.
there is a note in the preamble stating that V1mcg tables are conservative figures for all weight & bleed configurations. so I suppose the correction "bleeds off" is already taken into account & you will not find specific correction tables, unless you contact Mr.Boeing & ask. highest V1mcg for B738 is 106kts(-60°C & -2000ft press alt. 26K engines) well below your normal V1. eg. tow 60ton. flaps 5, V2= 80+60ton=140kt with V1 a few kt.lower. k.regards, bm.
23rd Jun 2012, 10:49
Interesting, the DDPG/MEL we use doesn't mention any of this, no adjustment necessary, just remain below FL250 and everything is fine.
But then, we don't have the Vmcg table in the QRH anyway, as the EFB takes care of that.
23rd Jun 2012, 12:33
Thank ya'll for the inputs.
At a second look I could indeed find the statement in our Performance preamble that "The V1 (MCG) presented in this manual is conservative for all weights and bleed configurations".
Denti, out of curiosity, does your DDPG mention anything about performing No Engine Bleed Take-off and Landing, SP 2.5? With a slight modification to keep the right AC Pack OFF and Isolation Valve CLOSE.
Hi guys, I found this on my MEL
"OPERATIONS (O) For remarks or exception
I) 1. When dispatching with one operating pack supplied by engine bleed air on takeoff:
A. Determine V1 (MCG) based on engine bleed for packs OFF.
B. Determine takeoff performance based on packs AUTO. 2. 3. 4. 5. 6. Mel737-NG 21 p01-02 r5-5 021109 1328 Limit altitude to FL 250.
For B737-76N and B737-73V only, use only one chiller inflight.
Position the associated PACK switch to OFF.
Position the ISOLATION VALVE switch to CLOSE.
For increased air flow when the flaps are extended (takeoff and landing), use the APU to supply bleed air to the operating pack.
A. Right pack Inoperative 1) Do the Supplementary Procedure – Air Systems “No Engine Bleed Takeoff and Landing” (Refer to the Flight Crew Operations Manual).
NOTE: Keep the PACK switch to OFF and the ISOLATION VALVE switch to CLOSE.
B. Left pack inoperative – PRIOR to takeoff or landing
1) Engine No.1 BLEED air switch to OFF
2) R PACK switch to AUTO
3) L PACK switch to OFF
4) ISOLATION VALVE switch to OPEN
5) Engine No. 2 BLEED air switch to OFF
6) APU BLEED air switch to ON"
I guess that you have to make a no engine bleed take off because you must leave the inop pack switch in OFF, so the operating pack will work on high and will demand more bleed, so.... what happened if some engine fail?, you will be climbing and accelerating with less power than what the engine can really offer. Maybe this can also affect your V1 (MCG).
26th Jun 2012, 21:58
M.82, same here!
27th Jun 2012, 01:26
The bleeds off take off is only for when you desire more airflow, as it says there. The actual MEL is indented to make that easier to read.