Jughead135

That's the way it worked on the E-model series (i.e., TF-33 engines), and probably the same on the A-model (J-57 engines, though I have no direct experience with those). The R-model (CFM-56 engines; virtually all -135s still flying now have them) rudder system was modified. The one CB controlls power to the rudder power switch, and the other controlls power to the high/low range valve. Power failure leaves each valve wherever it was when power was lost. Standard briefing these days is to have the nav/boom ensure rudder CBs are in (set) in any uncommanded rudder situation, to ensure that the switches do what they're supposed to do.

Agreed, cutting off the rudder power altogether was the correct first step--the tragedy is that the crew wasn't trained in recognizing this, let alone accomplishing it.

Flyinhigh

You are correct about the rudder power on the R model. I spent 17 years on the A and 5 years on the R. Got confused. As I recall, turning off the rudder power also killed the SYD and the EFAS. Sort of one stop shopping.

blastoff

That's what I remember too. It was also a Boldface item.

CAFB 04-12

The Dutch roll was caused by a malfunctioning SYD, which is why it occurred at low altitude. An uncommanded yaw (crab) also occurred immediately after takeoff causing some controllability issues for the copilot who was flying the departure.

The AC identified a malfunctioning SYD but didn't turn it off. During a turn to return to base the pilot used rudder to coordinate the turn. This, combined with the oscillating SYD caused the vertical stab to fail. The tail departed the aircraft which caused an unrecoverable pitch down.

The sim does not replicate Dutch roll. Crews are taught that Dutch roll is almost always corrected naturally by the SYD. The only rudder malfunction crews regularly practice is a full-travel hard-over of the rudder, which is quickly diagnosed as such, and the corrective action is boldface.

A couple months prior to the mishap this aircraft experienced an identical malfunction. The crew turned off the SYD and returned to base.

I was surprised at how quickly this mishap developed.

Flyinhigh

It has been over 20+ years since I flew the R model, but wasn't the SYD always engaged for yaw control? As I recall we pretty much flew the R with our feet flat on the floor or just resting on the rudder pedals. The SYD replaced the rudder axis of the autopilot that was used for yaw control on the A model. You would engage the rudder axis right after takeoff as soon as the water injection ran out (I am really dating myself now). The EFAS on the R model is used for rudder assist during takeoff in the event of an outboard engine failure and worked in conjunction with the SYD to apply up to 10 degrees of rudder below 160 knots. The EFAS gradually decreased rudder authority until all you had was a SYD for normal yaw control. If it was a SYD malfunction, the altitude should have had no bearing on the malfunction. Dutch roll is dutch roll.

CAFB 04-12

All true. I normally only ever used the rudder for crosswind landing.

TankerDriver

This info is completely wrong.

We really need to be careful talking about privileged information on open forums.

But, in talking about the dutch roll characteristics of the KC-135; if you turn the SYD off in flight, even at 3,000 feet in the traffic pattern, the airplane will dutch roll. It is very subtle at these altitudes, but it's there and the aircraft feels very sloppy without the SYD on. Once you get up into the high teens/low 20's, the dutch roll becomes very prominent, which is where Shell 77 started having issues.

Despite poor training in this area of aerodynamics, there were significant mechanical issues with this jet's PCU, which had a history of having issues. This jet is not alone.

I've always thought our flight control check was hard on the rudder. The dash 1 talks about aligning the aircraft into the wind if you cannot manually center the rudder before turning the rudder power on during the preflight and I can guarantee that most of us don't do this (are we really going to delay a mission to get the jet towed into the wind??). That rudder is the size of a two story barn door, which slams from full right or left to center during strong crosswinds when you turn the rudder power on. Years of doing this is most likely causing quite a bit of wear in the PCU's that eventually rears its ugly head.

Be careful guys. These jets are getting old. If something doesn't feel right, turn it off if you're in the air and land. If you're on the ground, hand it over to maintenance and let'm take a look at it.

CAFB 04-12

+1. That abovetopsecret website is just strange.

However, AIB info is public, and therefore free-game in my opinion.

SIB info is privileged and should only be used in a privileged setting to improve safety awareness.

blastoff

+1

And refuse the airplane if you're not satisfied with what MX tells you or oddities in the Forms. You'll survive the carpet dance. They made you an Aircraft Commander for a reason.