PPRuNe Forums - View Single Post - 737-500 missing in Indonesia
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Old 16th Apr 2021, 21:30
  #789 (permalink)  
tdracer
 
Join Date: Jul 2013
Location: Everett, WA
Age: 68
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I posted about this previously, but it's many pages back so I'll go there again:
The 737-3/4/500 used CFM56-3 engines - cable controlled (not FADEC). Cable controlled engines are subject to excessive down stream cable loads due to things like damaged push/pull cables, corroded or seized pulleys, etc. These high cable loads can overcome the friction clutches that connect the system to the auto throttle drive, allowing the throttle to slip and not respond to auto throttle inputs. It's not a design flaw in so much as it's an overall system limitation when using cable controlled engines with an auto throttle since there needs to be some sort of clutch mechanism to allow manual override of the auto throttle.
Given this aircraft had recently come out of storage, and apparently been experiencing this issue since it came out of storage. My guess is they had excessive cable loads on one throttle due to corrosion while the aircraft was stored. Checking/cleaning connectors won't do anything to correct a damaged throttle cable system - maintenance has to actually go and troubleshoot the cause of the high loads.

The 737NG series uses FADEC CFM56-7 engines - FADEC engines are not susceptible to this sort of problem since they don't have throttle cables.

Last edited by tdracer; 16th Apr 2021 at 21:58.
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