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Step on the ball in IMC: you're in IMC, in a multi-engine airplane. There's a loud bang and a horrible vibration. Where do you look next and what do you do?

In 1998, a United 747 took off into a low overcast from San Francisco bound for Sydney, Australia. Just after going IMC there was an explosion. Instantly, the airplane yawed and banked right.

The first officer banked left, raising the left aileron and left spoiler. The airplane rolled left but yawed further right. It lost airspeed and began to settle, triggering a stall warning. The FO lowered the nose only to hear, "Terrain! Pull-up!" from the ground proximity warning system. The FO recovered, but area switchboards still lit up with residents reporting the belly of a 747 passing one hundred feet overhead.

The number four (right-most) engine had experienced a compressor stall. The crew landed safely but good luck played too big a part. The asymmetric thrust caused the yaw, which caused the bank, requiring rudder, not aileron. The crew hadn't trained on the right procedures recently and didn't react correctly. The same is probably true for many multi-engine pilots, including me. It also signals a hole in the training curriculum for engine failure in IMC in multi-engine airplanes.

Ask the Experts

I augmented my twin-Cessna training at Flight Safety with a local instructor who is also an FAA examiner. We ran engine-out scenarios in his simulator. He insisted that I "step on the ball," faster with an engine out. In our debrief, I countered his recommendation by saying the needle or heading was primary. He was adamant that the ball was the primary instrument.

"Show me in writing," I said, thinking that that would quickly settle our debate.

We researched our libraries expecting to find the definitive answer to "What is the primary instrument for detecting and controlling sudden yaw in IMC in a multi-engine airplane?" We failed.

Instrument-training literature is for single-engine pilots who don't encounter sudden yaw. Multi-engine training texts cover bank and yaw control but not referencing the ball to control yaw with rudder or to the AI to control bank with ailerons.

I asked 20 multi-engine instrument pilots, one at a time, "I'm doing a poll. After taking off into low IMC, if you feel yaw and you suspect engine failure, what's the first instrument you look at?"

My results aren't statistically significant but they illustrate there's anything but unanimity. Answers were about evenly split between needle, ball, heading, and artificial horizon. But the most interesting response came from a United crew.

A year had elapsed since United's incident when I was disembarking as a passenger after a long Boeing 757 flight. I stopped by the flight deck and asked if they had time for a question.

"Sure," the captain said, as both he and the FO turned toward me.

"I fly a Cessna 310. I have a question triggered by United's 747 engine-out last year," I said. Then I asked my poll question.

"You know what, and you can't repeat this," the captain said, "but we're not trained for it. Except for the military, I've never done anything but V1 chops on the runway. It's been 20 years since I've done one just after takeoff."

"Same here," the FO said.

I was aghast and it must have showed on my face.

"Now, I'll tell you, it's just starting to change," the captain said, apparently not wanting to leave me empty-handed. "Just two weeks ago I got some training because of that incident. Now, we're taught to move the wheel like this to level the wings," the captain said, as he rotated the wheel a little to the right. "Then we're told to apply rudder in the same direction, like this," he said, as he tapped on the right rudder pedal with his right foot. Still, we've never done anything but V1 cuts on the runway, which is all the FAA requires."

In my dismay I forgot to ask, "But what instrument are you looking at as you do that?" Instead, I blurted out, "Where's the ball?" They both turned in their seats, facing their darkened glass panels.

"Uh, it's here someplace," the captain said.

I heard a switch click and the glass started coming alive.

"Let's see. Maybe we don't have it selected," the captain said.

I leaned in over their shoulders to join in the search and found it first. It was a physical--not electronic--ball, an inclinometer, mounted permanently at the base of the AI.

"Ah, yes, of course. Right there," the captain said, appearing sheepish. "But we're taught to ignore it. It's not reliable. It doesn't work in jets."

From that I could safely deduce that they don't use the ball as a primary yaw control instrument.

Weeks later I saw Barry Schiff, the aviation writer, having lunch in Camarillo, Calif. I told him my story verbatim, including the claim that balls don't work in jets.

"Sure they don't," said Schiff. "Didn't you know they suspended the laws of physics in jets?"

Step on the Ball

With so little unanimity on what is the primary instrument for yaw control in a multi-engine airplane with an engine out, there is also no effective standard. The consequence is that at least some otherwise well-trained pilots will respond anemically, rather than robustly, to an engine out. Yet, I do now have a standard for myself: Step on the ball.

Considering my poll, deduction, and comparative experimentation with the AI, DG, needle, and ball in a simulator and an airplane, I've concluded the ball is the only source for uncoordinated yaw detection. Step on the ball. That reveals the dead foot and dead engine and starts the verify-and-feather sequence.

Noise and kinesthetic seat-of-the-pants senses-normally verboten in IMC--are a reliable indicator that something is wrong. But for seconds after an upset there is a mystery as to the cause and required action. The step on the ball and power up is now where I start.

United's incident was eight years ago but it was a recent crash that renewed my attention. The pilot of an aircraft like mine, a Cessna T310R, crashed into mountainous terrain near Heber City, Utah.

At 10:24 the pilot, in IMC, told Center he had lost manifold pressure in his left engine. Center cleared him to descend from 16,000 feet to 14,000. But radar showed the airplane reversing course.

At 10:25, the controller asked the pilot if he had reversed course due to his engine problem and the pilot acknowledged he had. At 10:26 radar contact was lost. The wreckage was found at 9300 feet, in a nose-low, high-speed impact pattern.

If there is one good reason to own a twin it's that recovering from an engine out in high cruise should pose little problem. Yet, it took just two minutes for this poor fellow to crash from his first report of a problem.

I experimented in a simulator. Cruising at 16,000 feet, with the autopilot on, I gradually reduced manifold pressure on one engine. The autopilot pitched up and the airplane slowed. The autopilot banked the airplane to stop the turn, but because it's not connected to the rudder, the airplane skidded more and more. Then it stalled, rolled, and spun.

Operating at a high altitude in a turbocharged airplane may complicate things, but this crash, if ever there was one, is a call to action to raise the bar for better and more recurrent multi-engine IMC training.

The United 747 lost more altitude than you might, due to having spoiler-augmented ailerons which killed lift in a bank on the lowered wing. The fuselage in sideslip killed lift at the root of the right wing.

Unless that's what you fly, you won't have those problems but, perhaps like the 310 pilot, you may have others. Raising the sinking wing with aileron increases adverse yaw, which increases the yaw problem on any airplane.

You must choose your own recovery plan, but I encourage you to experiment with a simulator and/or safety pilot to find ways to mitigate the IMC, engine-out risk.
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Title Annotation:PRACTICALITIES
Author:Robinson, Frank
Publication:IFR
Geographic Code:1USA
Date:Apr 1, 2007
Words:1325
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