Lessons learned about wind and mountain waves.
As I sit to write this, the major theme in my life these past few weeks has been wind. I say that because, first and foremost, we are right now involved in cleaning up our Florida horse ranch from the effects of Hurricane Irma—which, thankfully, amounted to only a half-dozen fallen trees and, literally, an infinite number of tree limbs scattered across our acreage.
The second reason these past few weeks have involved wind is that I was concurrently producing an audiobook version of Harrison Jones’ nonfiction book “Miracle on Buffalo Pass: Rocky Mountain Airways Flight 217.” Reading for the audio version got me to thinking about experiences with wind-induced dilemmas from my own aviation past.
The book itself is an in-depth analysis and interview with nearly all the survivors of the Rocky Mountain Airways Twin Otter turboprop that crashed in a blinding blizzard at the very top of one of the most inaccessible spots between Denver and Steamboat Springs, Colorado on Dec. 4, 1978.
We follow the passengers and crew through their experience, and then the bands of rescue personnel who mobilized immediately to attempt to locate the wreckage and any potential survivors before they would invariably freeze to death on that desolate mountaintop.
As the NTSB later concluded, the Rocky Mountain Twin Otter encountered an unforeseen severe mountain wave which, when combined with some airframe icing, prevented the commuter airliner from climbing above 13,000 feet (the MEA in that area was 16,000 feet) and the airliner was then gradually forced down into the terrain, just barely clipping the top of the mountain at Buffalo Pass.
The first miracle was that everyone survived the initial impact with the crest of the mountain, but if rescue folks didn’t locate them quickly (no one knew for sure where they had gone down, and it was the middle of the night in a driving blizzard), none of them would survive.
As the NTSB pointed out in the accident report, one of the things that disguised what was happening was that the mountain wave the flight was involved with was quite smooth. With no wind-induced turbulence to tip the crew off, the initial symptoms of decreasing climb performance seemed to be more related to either engine power output or airframe icing. When the pilot in command is not understanding why something is happening, it’s far more difficult to come up with a reasonable plan to correct the problem.
My own experiences with mountain waves were certainly nowhere near as dramatic, but they were personally attention-getting. Being more of a flatland pilot, my initial exposure to the effects of wind across undulating terrain came from those small bumps in the earth around Kentucky and West Virginia that we Easterners call mountains.
About 50 years ago I was skittering around Eastern Kentucky in, if my memory serves me correctly, a Cessna 140 with a 90 hp engine. It was a breezy day—nothing too outlandish—and I was giving a student some dual in the art of crosswind landings at an outlying grass field we often used.
After a half-dozen acceptable takeoffs and landings in the quartering wind that was 20, with maybe gusts to 25, we left the airport for a little local flying up higher to get away from the bumps.
After a few steep turns and whatever else I thought the student could use, I figured that we’d top off our day with a simulated engine failure, then head back to the barn. I chopped the power and announced: “Engine failure.”
The student picked a field below in a reasonably wide valley between two rows of hills, and set up an approach to a large pasture. Down to about 300 feet everything looked fine, so I announced, “The engine is working again; just go around and head back to the airport.” The student complied.
He did everything right. So did the airplane. But Mother Nature did not. The student pushed the power up to max; 90 horses surged into the prop, and he turned us toward the airport that was on the far side of the next ridgeline. But we were, I figured out later, on the leeward side!
At max power and max climb speed, we were barely holding altitude—and the ridgeline in front of us was getting nearer! I was getting less comfortable with every passing moment, until I finally said, “I’ve got it.”
Suspecting there was something now wrong with our engine, I did a snappy one-eighty to head back for our simulated emergency landing field—one that I figured we might need for real. Partway back—and, it turns out, away from the effect of the downward wash of wind over the ridgeline—we began climbing normally again. We climbed to a higher altitude, then crossed that ridgeline far above the mini-mountain wave effect beneath us.
Many years later I was in a light twin flying between northern Colorado and Montana, where there are some real mountains by anyone’s standards. It was a breezy, clear day and I was flying at the MEA, enjoying the view of the ridgelines and canyons that passed below.
What I noticed first was the airspeed slowly trickling away as the autopilot kept pitching us up a little more as it tried to hold our altitude. Again, my first thought was that something was wrong with the power output from the engines, or at least one of them.
Yet all the engine gauges were middle of the green. They sounded fine, too. So what could be happening? It took me a few moments to see the obvious: the line of higher mountains to the northwest of my location were at a right angle to the prevailing wind. We were apparently in a downwash of wind from them.
I requested a higher altitude from ATC, pushed up climb power and while the rate of climb was a little lower to begin with, a few thousand feet of climb later, the performance numbers went back to normal as we got above the downward effect of the distant mountain wave.
But don’t think that only smaller airplanes are susceptible to this sort of wind-induced dilemma. About 30 years ago I was the captain of a Boeing 737-400 headed westbound to San Francisco over the middle of the biggest rocks in the Rockies. We were at FL310 on a windy day, with our ground speed being clobbered by the constant westward flow. Still, the sky was smooth—so all was well, right?
First clue: the sense of the airliner trying to climb, the autopilot rolling in nose-down trim and pulling off engine power to keep us at altitude. I commented to the copilot something insightful, like, “What the hell?”
I disconnected the autopilot, reduced the power on both engines until they were back at idle—and we were still being propelled upward at over 2,000 feet per minute! It was hard to believe what the gauges were saying. I pulled out full speed brakes, and still we were climbing!
The copilot told ATC that we couldn’t hold altitude; that we were being pushed up. We got to 35,000 feet and I began to seriously worry because, even thought the sky was still smooth, if we went much higher the air would be (in a manner of speaking) too thin to keep the wings from stalling—“coffin corner,” it’s called.
Then we hit the turbulence, which started at severe and quickly got worse. Our big Boeing airliner was simultaneously being pushed upward and churned all around the sky! We needed to get down—quickly—before the wings decided to do the job for us.
I was just about to call for gear down (at this airspeed, it would have probably done some gear damage) to get more drag to stop us from climbing when, in the blink of an eye, the washing-machine sky we were in went dead calm.
We had popped out of this mountain wave-induced wind machine at 35,400 feet. We stopped climbing, the airspeed began to drop, and I then pushed engine power to a low cruise setting. After coordinating with ATC, we turned off our route that had us headed toward the highest mountains and eventually drifted back down to our assigned altitude of FL310.
So that’s what I spent Hurricane Irma doing: narrating the book “Miracle on Buffalo Pass,” which is about the results of a wind-induced accident, while listening to the winds howl around my own home.
Like an old captain once told me nearly 60 years ago, “Son, don’t fool too much with Mother Nature. She can win anytime she wants to.”