If you haven’t read it already, check out Bill Ardolino’s article on the helicopter war in eastern Afghanistan, which was published at Wired’s Danger Room. He explains some of the difficulties in operating helos in a harsh environment, and also details how they supported US troops during two recent clashes with insurgents in Khost province. (He was involved in one of those clashes, in the Sabari district, which resulted in six soldiers wounded; he detailed that contact here.) Above is highly edited video of the first engagement, in the Musa Khel district, which was also described by Bill at Danger Room. An excerpt from his report:
Afghanistan’s environmental challenges to flight are based on the maxim of “hot, high and heavy.” It’s shorthand for how elevation and temperature interact to impact an aircraft’s power and lift at a given weight.
As altitude and temperature increase, the density of the semi-tangible bed of molecules pushing off of the rotors and airframe lessens, causing the engines to generate less and less lift from larger and larger amounts of power. Inversely, colder temperatures and lower altitude enable greater power efficiency and overall lift.
‘This is like living in a prairie storm half the time over here.’
As pilots transit the mountainous, thin air of Afghanistan, they constantly monitor two metrics: “density altitude” is the aircraft’s effective altitude when factoring in the temperature. For example, while the aircraft may be physically at 5,000 feet above sea level, the density altitude may be 7,000 feet when factoring in a hot temperature.
The other metric is “tab data,” a measure that calculates what the helicopter’s maximum power is at any given combination of altitude and temperature. When this max power is cross-referenced against the weight of the aircraft at the time, pilots can determine whether they have enough lift to sustain a given flight maneuver or mission in a given area. That helps them avoid an unplanned landing or crash. But even with due diligence, Afghanistan presents unique challenges.
“Afghanistan is weird,” explains Black Hawk pilot Chief Warrant Officer 2 Steve Atencio. “Temperature change doesn’t occur the same as it does back home, for some reason. There is usually a standard lapse rate [in temperature]. You gain or lose 2 degrees [as you descend or ascend a certain altitude], but for some reason here, it’s more dramatic. We’re continually looking at that tab data to ensure you won’t have a mishap.”
The danger of thin air was starkly illustrated a couple of weeks ago, when a Tigershark Apache helicopter crash-landed at about 11,000 feet. Though the incident is still under investigation, early reports suggest the pilot banked too hard for the thin air, and lost sufficient lift under the rotors. He successfully crash landed on a mild slope — no easy feat among the jagged ridges in the area of the crash — but the aircraft was eventually destroyed after several failed attempts to airlift it out of the mountains with twin rotor Chinooks.
And if the ad hoc calculations regarding heat and thin air weren’t complicated enough, helicopter pilots must also pay attention to Afghanistan’s fickle mountain winds. When an aircraft flies into a head wind, it loses speed but gains performance; the rushing wind acts as an air foil that grants the helicopter maneuverability. If the pilot makes a sudden turn perpendicular to or opposite the wind, the aircraft quickly loses this extra performance, and a pilot’s failure to compensate — for example, starting to pull up from a dive too late — could precipitate a crash into a mountainside.
Eastern Afghanistan’s sudden onsets of harsh weather present a real danger to aviators.
“It’s not just high, hot and heavy mountain flying, it’s the weather that you throw on top of it,” said Kramer. “This is like living in a prairie storm half the time over here. You can’t put airframes out in this stuff. Am I afraid of enemy fire? Sure I am, like everybody. But I’m most afraid of the weather and how it will sneak up on you, and consume you.”
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