Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Boeing 737 NG and classic questions

Tech Log The very best in practical technical discussion on the web

Boeing 737 NG and classic questions

Old 14th Jul 2019, 04:38
  #1 (permalink)  
Thread Starter
 
Join Date: Aug 1998
Location: australia
Posts: 313
Boeing 737 NG and classic questions

Hi All,



Some opinions on the below topics would be greatly appreciated;

1. What target speed would you use for a engine Re light envelope on the classic and NG above FL240 since there is no envelope for this, would you use the speed targets suggested in the loss Of thrust on both Engines IE: At or above FL270 set airspeed to 275 knots. Below FL270, set airspeed to 300 knots?



2. In the engines section of the FCOM on the classic and NG, Boeing recommend the below techniques, however I cannot find reference to this in the QRH maneuverer section and or FCTM???,



It is more relevant for the NG why would Boeing think of this, especially in such a pressured time critical situation?

B737 Classic

With the PMCs ON or OFF, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent.

B737NG

If the EECs are in the alternate mode, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent.

Last edited by downwind; 14th Jul 2019 at 08:57.
downwind is offline  
Old 14th Jul 2019, 08:23
  #2 (permalink)  
 
Join Date: May 2002
Location: U.K.
Age: 42
Posts: 158
As I’m going to be starting a 737 type rating in the Autumn for a new job, I have been looking at this website The Boeing 737 Technical Site and have bought the very good book that contains the same information. Might help!
Jump Complete is offline  
Old 14th Jul 2019, 10:45
  #3 (permalink)  
 
Join Date: Apr 2012
Location: In Space
Posts: 603
To answer your first question.

You won't be above FL240 in an OEI configuration, because the AC cannot maintain altitude. This is why the envelope is up to FL240.

If you lose an engine in-flight, you would drift down to your ENG INOP CRZ altitude.

In regards to your second question, I'm a bit lost in what you're trying to ask.
B737900er is offline  
Old 14th Jul 2019, 10:48
  #4 (permalink)  
 
Join Date: Jan 2018
Location: Amantido
Posts: 843
I think he is trying to ask why we would not overboost the engines immediately in case of imminent terrain contact?
Banana Joe is online now  
Old 14th Jul 2019, 11:14
  #5 (permalink)  
Thread Starter
 
Join Date: Aug 1998
Location: australia
Posts: 313
Hi All,

Let me re-phrase the questions it was a bit vague initially!!!....

Some opinions on the below topics would be greatly appreciated;

1. Let’s assume you have had a straight flame out on your engine (no damage/vibration etc) and on the drift down you elect to re start the affected engine you are above FL240 which is the engine re-light envelope. What target speed would you use for the engine Re-light envelope on the classic and NG above FL240 since there is no envelope for this, would you use the speed targets suggested in the QRH loss of thrust on both Engines IE: At or above FL270 set airspeed to 275 knots. Below FL270, set airspeed to 300 knots?

2. In the engines introduction section of the respective FCOM's on the classic and NG, Boeing recommend the below techniques for overboost, however I cannot find reference to this in the QRH maneuverer section and or FCTM???

B737 Classic FCOM

“With the PMCs ON or OFF, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent.”

B737NG FCOM

“If the EECs are in the alternate mode, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent.”
Question.

It seems rather imaginative from Boeing to suggest this under a extreme high pressure situation this action "only during emergency situations when all other available actions have been taken and terrain contact is imminent" also to add the PM would be looking at the overhead panel rather than supporting the PF in their efforts to avoid the terrain?

Based on the above FCOM statements why would Boeing mention this, after having performed this in the B737NG sim for a bit validation it seems rather crazy this recommendation and contrary to QRH maneuverer section and FCTM. Please note this technique/procedure seems more relevant to the B737NG due to the EEC’s.
downwind is offline  
Old 14th Jul 2019, 12:01
  #6 (permalink)  
 
Join Date: Jun 2019
Location: VA
Posts: 55
I’m not going to dig out my QRH right now, but it seems the first question is a separate situation from the second question. Also I’m an NG guy so I can’t speak for classics.

First question I would answer whatever speed/altitude is provided by the QRH with the understanding that lower and faster is better. That is if you don’t get a relight the first time then descend and speed up. Every time you cycle the start levers the aircraft switches EEC’s (which is why you keep cycling the start levers on dual flameout), so if one of the EEC’s is bad, then another attempt will switch to the other one. Remember that you will have your APU to assist.

Second question. EEC will protect the engines from overboost in normal mode. They may not do so in alternate mode. The statement in the manual regarding overboosting is simply Boeing way of saying that it is better to overboost the engine than crash the airplane if a moderate amount of additional thrust would have made the difference.
Tomaski is offline  
Old 14th Jul 2019, 13:35
  #7 (permalink)  
 
Join Date: Apr 2012
Location: In Space
Posts: 603
I've personally have not seen an OEI CRZ above FL240 on the NG or CL, maybe FL245 when empty on the NG.

So initially, you would drift to <FL240.

The statement regarding the over boost is talking about what thrust protection is available when the EEC is in the hard mode or alternate. To protect Boeing, they include the statement about when to over boost the engines. It has nothing to do with Engine failures.
B737900er is offline  
Old 14th Jul 2019, 18:34
  #8 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,325
By regulation, it's necessary to demonstrate the in-flight start envelop, using an engine that is at stabilized windmill conditions. Given that the aircraft will struggle to maintain an altitude above 24k with an engine inop - it's very difficult to get the data to validate the start envelop above that altitude.
tdracer is offline  
Old 14th Jul 2019, 22:09
  #9 (permalink)  
 
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 821
Originally Posted by downwind View Post
In the engines introduction section of the respective FCOM's on the classic and NG, Boeing recommend the below techniques for overboost, however I cannot find reference to this in the QRH maneuverer section and or FCTM???

B737 Classic FCOM

“With the PMCs ON or OFF, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent.”

B737NG FCOM

“If the EECs are in the alternate mode, advancing the thrust levers full forward provides some overboost and should be considered only during emergency situations when all other available actions have been taken and terrain contact is imminent.”
Question.

It seems rather imaginative from Boeing to suggest this under a extreme high pressure situation this action "only during emergency situations when all other available actions have been taken and terrain contact is imminent" also to add the PM would be looking at the overhead panel rather than supporting the PF in their efforts to avoid the terrain?

Based on the above FCOM statements why would Boeing mention this, after having performed this in the B737NG sim for a bit validation it seems rather crazy this recommendation and contrary to QRH maneuverer section and FCTM. Please note this technique/procedure seems more relevant to the B737NG due to the EEC’s.

First of all, nowhere does Boeing say you have to look at overhead panel during the manuever itself. You should be aware whether you are operating with PMC OFF or EEC in ALTN mode as:
  1. There is a master caution indication, after which you will either perform QRH actions or if on the ground, dispatch the aircraft in accordance with MEL/DDG.
  2. If this is the case, I imagine both of the pilots will be VERY aware that they are operating the aircraft in a non-normal configuration and some normal and non-normal procedures must be adjusted to account for the previous failure, as Boeing QRH only takes single failure into account.

Second, every single B737NG QRH I have seen contains this note under the Manuevers section (for both Terrain and Windshear escape maneuvers), which I believe is quite self-explanatory:

Note: *Maximum thrust can be obtained by advancing the thrust levers full forward if the EECs are in the normal mode. If terrain contact is imminent, advance thrust levers full forward.
​​
Additionally, the B737NG FCTM also provides similar guidance in the "Maximum thrust" section:

The term “maximum thrust” is used in various places in the FCTM and the
FCOM. Maximum thrust is attained:
• for airplanes with electronic engine controls (EECs) operating in the
normal mode, by advancing the thrust levers full forward
• for airplanes with EECs operating in the alternate mode, by advancing
the thrust levers to the full rated takeoff or go-around limit only.
Advancing the thrust levers to the full forward stop should only be
considered if terrain contact is imminent.

Third, on the B737 Classic one should never firewall the thrust lever or advance them beyond full rated thrust (TO / GA N1 limit), unless terrain contact is imminent, regardless whether the PMC is operative or not, as the engines have no protection.
FlyingStone is offline  
Old 16th Jul 2019, 03:32
  #10 (permalink)  
 
Join Date: Jan 2013
Location: Seattle Area
Posts: 53
The classic had what was referred to by some in the engineering community as a "postage stamp" windmill inflight start envelope because it was so small. The envelope tops out at 24,000 feet because that was all that was successfully demonstrated. It wasn't because the airplane couldn't hold that altitude. The accepted test technique when you are at altitudes above the point where one engine can hold altitude is to descend through the target altitude at the target speed and initiate the start attempt at approximately the target altitude. Boeing would have preferred to have a 28k or 30k capability, but the engine couldn't windmill start there. At the altitudes where it could windmill start, it required an airspeed (and corresponding windmilling conditions) of I think 300 knots, which was well above the best glide slope speed.

The NG could accomplish stabilized windmill starts at quite a bit lower speed - 260 knots IAS I think it was - much closer to the all engine out best glide slope speed. It still was not a consistent starter above 24,000 feet.

Regarding use of the engines beyond rated thrust, Boeing was just telling crews the conditions under which additional thrust beyond max rated thrust for the airplane model may be available, and advising them to use it as a last resort.

Just in case some non-NG pilots aren't aware, the NGs that are purchased with engines rated lower than the maximum approved rating for the airplane model (700, 800, etc) have the ability to access the maximum rated thrust for that model in an emergency by pushing the levers to the stop in the normal EEC mode as well. (This is the "maximum thrust" feature mentioned in a post above.) As far as I know that is unique to the 737NGs (and maybe Max?) among Boeing models.
Dave Therhino is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.