Aviation Mountain Gods: Enter the Mosh Pit
- Erika Armstrong
Aviation Gods thrive on watching pilots learn. They are proud of us as we muddle our way through our ratings while they throw a variety of weather and mechanical challenges at us. They giggle as we bounce a few landings, panic when we realize we're lost, and they hold their breath when we forget to turn on the carburetor heat. They cheer as we strap into our first jets and yell "Yee Haw" each time we get past V1 and rotate. But, they especially enjoy the day we think we know it all. My Aviation God smirked the day it was time to show me what mountain flying really meant and from that moment on, I knew I'd never know everything about aviation.
I'm from Minnesota (now, say that again with a Minnesotan accent). I learned to fly at 900 feet above sea level so the aircraft I flew performed as expected despite the twisted airframes of the trainers. As I progressed into the corporate jet world, the Citation II I was flying felt like a rocket (but, since this was my first jet, I didn't think it could get better than that!). Even on hot, muggy Minnesota days, the Citation happily complied with whatever I asked of it. When the charter company I flew for needed to provide pilot services to a client who wanted his jet flown to Telluride each weekend, I nearly broke my arm trying to raise my hand to volunteer first. Telluride. Shangri-La at 9,070 feet nestled in a box canyon surrounded by 14,000 foot peaks. After years of flying the flatlands of the Midwest, I was going to take on the challenges of Colorado airports.
I was typed in the Citation II, but was still very low time and happily flying as copilot. My first few trips to Telluride were with the chief pilot and I'm glad it was him who was flying because I could hardly stop looking at the scenery out the window. I flew in there before they took all the fun out of it and fixed the dip in the middle, installed EMAS, and added length to create the 6,900 foot runway it is today.
Since I was the enthusiastic new pilot, I gladly did all the performance chart calculating, weight and balance, and flight planning. I wanted to do it all. Based on performance charts, we had been going back and forth between no-flap takeoffs and flaps set takeoffs depending on the temperature. The Citation has single-slotted trailing edge flaps. Nothing fancy, pretty simple, but this simple choice almost cost us our lives.
I had made a dozen trips out to Telluride when the chief pilot's schedule put him over duty time so he couldn't cover the weekly trip. I was paired with a captain who I'd flown King Airs with, but had not flown the Citation with him. He was new to the Citation, but had twice as many total hours as I did, so I respected his opinion and assumed my roll as "copilot". Having a "copilot mindset" is something we sometimes fall into despite all that CRM training. Even though sitting in the right seat we are truly a CO (equal) pilot, it's sometimes simpler and human nature to delegate responsibility so we must remind ourselves that in this world of aviation, we're pilots, not humans. On this trip, I forgot to be a pilot first, human second, and I should have spoken up.
We had a 1000 departure and it was still chilly when we arrived at 0830, even though it was the middle of July. Our passengers notified us they'd be a little late, so we now had a noon departure and it had gone from chilly to toasty. I worked out our performance numbers and the charts said a no-flap takeoff. The winds were gentle, but swirling, so they weren't going to be any help and at any moment can turn into a tailwind. While waiting for the passengers, I told the captain we had to plan a no-flap takeoff. He looked at me like I'd said it was snowing out and replied that he'd never done a no-flap takeoff and that the runway was too short to risk it. Oh boy, challenge a new enthusiastic pilot and see what happens.
I went out to the airplane, grabbed the charts and showed him. As we were going through the variations, our passengers (the owner of the airplane and his guests – and one extra passenger who we didn't expect) arrived. The owner was an aviation enthusiast who never quite had the time to get the pilot certification but loved learning about it. He asked us what we were bickering about and I explained a little about drag and the flap/no-flap conundrum at Telluride. If we set flaps, we'll get off the ground quicker, but then we'll be in the air at a slower airspeed. No flaps, we need more runway but once airborne, have more speed and ability to climb. Since Telluride sits on a high plateau, it's disheartening to see the end of the runway coming up fast and knowing if you don't lift off, you're skidding off the end with a vertical drop down the valley which assures you're done learning. But, it's better to have the speed by the time you get there so your wings can not only fly, but climb as well.
Because we were having fun with the debate, it really didn't settle into my head the ramification of going against what the charts recommended. The captain was firm with his decision to go with flaps set and since this airplane had never come close to letting me down, I assumed it was not going to be a problem…it was the second touchdown on takeoff when I knew the ASSumption was going to make an ass out me.
It began with a gentle takeoff roll. We entered the runway and the captain did a slow throttle up for a smooth takeoff. He was so used to providing passenger comfort, he forgot how dangerous it can be. Takeoffs (and landings) at mountainous airports require assertive pilots and passenger comfort is not in the equation except a good passenger briefing about what to expect.
I called, "V1…(waited for what seemed like eternity here), rotate."
The captain pulled back on the yoke but nothing happened except a skip. He pulled back again and the airplane jumped and settled back down. We didn't take off so much as simply running out of runway and holding ground effect. As the steep drop to the valley opened up, the ground effect holding us up disappeared and we dipped into the valley. How many pilots can say they've flown below the runway they just departed from and lived to tell about it? Since we had no runway left, I yanked up the gear and even though the captain didn't call for it, he grabbed the flaps, put them up and flew down the valley as we gained enough speed to start a positive rate.
It only took ten seconds, and as a pilot you know what I mean when you simply deal with one issue at a time and then realize later that if you had done one more thing wrong, you wouldn't be around to worry about your wounded ego.
No one said a word as we finally reached positive rate and turned up valley towards flatter land. I stole a glance at my captain as I got ahold of ATC and could see he was as white as a ghost. To add to the joy, the owner of the airplane came up to ask us, "What the f*^& was that?" That was my captain's last flight for this customer. He told him so right then and there. The owner simply punched me (gently, I think) in the shoulder and said, "You were right, but you didn't have to teach us all a lesson."
It did teach us all a lesson, but especially me. I did many things wrong that day, but most of all, I didn't let the facts speak for me. I should have told the captain I was not departing unless we followed the guidance of the performance charts. It is rare that we ever fly on the edge of these performance charts but that day was it. It was hot, humid by noon, the winds were shifting enough that we probably had a tailwind, and we had one more passenger than we originally expected. I had calculated density altitude, but how much had it changed in the forty-five minutes between calculation and departure? Probably a lot at that elevation. It can be 35 F degrees at 0700 and 80 degrees F by noon at these high, thin-aired airports. So, to avoid being human, here are a few reminders about the important elements of high elevation airports.
DENSITY ALTITUDE (DA) - AN ANALOGY, YOU'LL NEVER FORGET
In plain English, let's think of air like a mosh pit and your airplane/wing is the lead singer about to jump into the mosh pit, expecting the audience to hold him up. When it's really hot, the audience members don't stand as close to one another because they stink and they're sweaty. So as the singer jumps into the pit, there is still lift, but not as much as if the audience was closer together. In contrast, if it was cold, the audience/air molecules would stand closer together, trying to stay warm. When the singer/airplane jumps into the pit, there is more lift when it's cold. Okay, it's really more complex than that, and I could go on about the laws of physics, but for a pilot sitting at the end of the runway looking at the mosh pit at the end, this is all I need you to remember.
Pressure also affects air density. The atmosphere has weight and it's heavier at the surface of the mosh pit than in the rafters above. Increasing pressure smooshes the mosh pit together – like putting all the audience members in the basement of your mosh pit auditorium. For every thousand feet you make them climb up, fewer audience members can climb that high (totally out of shape and they give up in percentages every thousand feet or so), so the difference in molecular compression due to pressure is much less in Telluride than as sea level. Simply, there are fewer people in the mosh pit at 9,000 feet to hold up your singer/airplane.
I live at 8700 feet in Colorado so I love taking my Minnesota friends and relatives to the bar their first night and buying them drinks. There is so much less oxygen here than what they're used to, their bodies don't burn alcohol like at home. For your airplane to create power, oxygen is required to burn the fuel. If you have less oxygen, you have less power. You still need the proper fuel/air ratio so even if you have plenty of fuel to throw at your engine, you still don't have as much air to burn with it. Sure, there are ways to compensate, but that's another article.
SWEATY MOSH PIT
I'm going to add one more important element in here which is harder to determine. If your mosh pit is sweaty (high relative humidity and high temps), hotter air can hold more water than cool air which means your audience members/molecules are all holding beers when it's hot so they have less ability to lift you/your singer. Your audience members/molecules will also be a little more sweatier and slipperier and it will have an effect on performance, but we don't really factor humidity percentages in most performance charts. Just be aware it's one more thing that might let your airplane down or drop your lead singer.
WHAT YOUR TAKEOFF WILL LOOK LIKE
The most disconcerting thing about high, hot altitude takeoffs is that the picture looks all wrong. Your peripheral vision will be screaming, holy cow, look how fast we're going, while your airspeed says "meh". Since we determined our mosh pit is pretty thin up here, we still need a certain airspeed to create the lift we need, so we're going to have to go faster to get enough molecules/audience members to lift us up. You'll actually be increasing your true airspeed which means your ground speed is going to increase, even though you're watching for your regular indicated airspeed, just like at sea level. You're not hitting as many audience members/molecules with your pitot tube so you'll have to go faster to hit the required number.
Pilots have relationships with their airplanes. Just like a marriage, you'll be going along, expecting your spouse to behave a certain way and then suddenly, they do the unexpected. You'll blame them for the errant behavior, but if you analyze the situation a little closer, you'll realize they did what they had to do.
Photo credit: summitpost.org
From the front desk of an FBO to the captain's seat of a commercial airliner, Erika Armstrong has experienced everything aviation has to offer. She is the author of A CHICK IN THE COCKPIT, aviation professor at MSU Denver, and Director of Instructional Design at Advanced Aircrew Academy where you can chose from 60 different modules, like mountain flying, for your flight department that can fulfill your Part 135 and/or IS-BAO/Ops Spec requirements. If you'd like to share your mosh pit flying story, she can be reached at firstname.lastname@example.org.