McDonald: A dangerous airport, especially for jets
Guest Commentary
The Aspen Times
The proposed FAA conforming remodel of Aspen/Pitkin County Airport’s runway, taxiway, and aircraft parking to accommodate longer wing and heavier (50 ton+) aircraft presents some safety concerns unique to Aspen.
Density altitude is a big deal for any pilot flying into Aspen. Thinner air means less engine power available for take-off/climb and significantly higher ground speeds/air speeds are required to give you the same indicated airspeed value and lift at sea level. The density altitude of Aspen on a 90°F summer day is near 12,000 feet. This qualifies the Aspen airport a classification of a “high and hot,” statistically accident-prone airport.
What makes “high and hot” airports particularly treacherous for jet aircraft are their already skill-demanding fast-maneuvering ground speeds at sea level are even made faster at high density altitudes, and this is not reflected by their indicated airspeed. Pilots use indicated airspeed as their primary flight instrument to regulate all modes of flight.
Adding fast-gusting tailwinds to already high-density altitude ground speeds increases greatly the chance of misinterpreting distance when avoiding mountainous terrain. This misperception of closing speed can result in a reflex turn which over banks the wing beyond what is specified by the indicated airspeed, resulting in an accelerated stall. Unless you are over 4,000 feet above ground to level your wings and pull out, you’re dead.
This happened in 1991 when a Learjet crashed by an accelerated stall initiated from over-banking beyond the indicated airspeed specified bank limits to make the runway. Note: Visual perception of high ground speed is only viscerally acknowledged for eye-hand coordinated response until you are close to the ground. Until then it’s only a number.
Observed: Typically when a jet aircraft executes a go-around from a landing approach, they put the pedal to the metal while making an accelerating left hand climbing turn between Shadow Mountain and Red Butte, completing a 180° turn before hitting Red Mountain.
This could be an intimidating, white-knuckle experience for the uninitiated, sea-level pilot. When the density altitude is kissing 12,000 feet, the indicated airspeed is reading 180 knots, but the ground speed is 217 knots (or 4.2 mile/minute) with winds aloft gusting at 25 knots. Maneuvering in tight airspace with fast ground speeds requires confidence, a calibrated eye and no misperception or hesitancy.
The current chance of landing long and fast on the runway in summer is statistically greater than in winter. This is in part because climate change has increased the frequency of high temperature, high density altitude days, where ground speed is significantly faster than indicated airspeed.
Under these conditions, landing at Aspen comes at you much faster. You’ll be passing Shale Bluffs with no time to think, and in the blink of an eye, you’ll be over the threshold flaring for touchdown. If the closing speed to runway is misjudged, which is statistically more likely for anyone who has been landing at sea level their whole professional career, the touchdown point can move far enough down the runway to require panic braking to stop. Such braking can blow out tires and or cause a runway excursion, closing the airport.
This seems to be a fairly common occurrence at Aspen’s airport of late. Just how long would it realistically take to move a 100,000 pound, crunched jet off the field?
Unfortunately, if this runway expansion is completed, not every 50+ ton aircraft that the FAA will allow to fly into Aspen will be the high-performing short-field, incredibly powerful Airbus A220-100.
It’s not the scheduled carrier you worry about, with their tried-and-true, by-the-numbers procedures tailored to Aspen. It’s the occasional sea-level flatlander charter pilot who is inexperienced with “high and hot” airports and mountain flying.
This proposed airport expansion most definitely increases the statistical chance that a 50+ ton passenger jet will land too long and fast, parking itself at Buttermilk or fly into a mountain. Is it worth the statistical risk?
Scott McDonald is an Aspen resident.
