Boeing 737-8: "stuck" rudder pedals during landing [pdf] | Hacker News Reader

Boeing 737-8: "stuck" rudder pedals during landing [pdf]

data.ntsb.gov

20 pointsmzs6 comments

reminded me of this likely unrelated history explained by Admiral_Cloudberg: "The crashes of United Airlines flight 585 and USAir flight 427: the Boeing 737 Rudder Defect - Analysis"

https://old.reddit.com/r/CatastrophicFailure/comments/adl0jk...

edit: rollout guidance servo is of early interest:

"On February 28, 2024, the Systems group met at the Collins Aerospace facility in Cedar Rapids, Iowa to examine and test the SVO-730 rollout guidance servo removed from the incident airplane. The testing was conducted to evaluate the effects that temperature “cold soaking” of the servo might have on the torque required to move the servo’s output crank arm. Testing at room temperature found that the torque to rotate the servo’s output crank arm was within design specifications. The unit was then “cold soaked” for 1 hour and the test was repeated. That testing found that the torque to move the servo’s output crank arm was significantly beyond the specified design limits. Because the servo output crank arm is mechanically connected to the rudder input torque tube, the restricted movement of the servo’s output crank arm would prevent the rudder pedals from moving as observed during flight 1539 and the test flight. Further examination of the SVO-730 rollout guidance servo will be conducted as the investigation continues.

> rudder SVO-730 rollout guidance servo that was disabled per UAL’s delivery requirements

Not great that a disabled component seems to have caused this issue :(

Did they intend to fly an unused multi-kilogram piece of hardware around the world burning fuel unnecessarily with every flight?

That's my understanding, yes.

When you consider air freight is worth ~$10/kg for cross-ocean flights, the decision to not remove 10kg of unused servo is worth about $700,000 per plane across the ~20 year expected lifespan of the plane.

And they probably do this on all their planes too, so perhaps multiply that by their ~200 plane fleet size giving a loss to the shareholders of $140,000,000.

That ought to be hard to justify at the shareholder meeting.

If you read the context given in the report, it mentions that this is done to change the plane's ILS rating from Cat-IIIB to Cat-IIIA. While I have absolutely no clue what operational/financial reason there might be to do this, I would guess they want to reenable the servo at some later point.

(The plane might also just not be certified to operate without that servo; as shown by this incident the servo still has some impact even when it's disabled.)

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