Buzz
Tom Farrier:
This has been attempted before, with deadly results. For instance, in October 2004, the crew of Pinnacle Airlines 3701 [PDF] was flying a repositioning flight, transferring an empty aircraft between airports.
Their flight was supposed to reach 33,000 feet, but they instead requested to climb to 41,000 feet, the plane’s maximum operational altitude. Both engines failed, attempts to restart them were unsuccessful, and the plane crashed and was destroyed.
The National Transportation Safety Board concluded that the main causes of this accident were: (1) the pilots' unprofessional conduct, deviation from standard operating procedures, and poor airmanship, leading to an in-flight emergency they could not recover from, partially due to insufficient training; (2) the pilots' failure to prepare for an emergency landing in a timely manner, including the lack of immediate communication with air traffic controllers after the emergency about the loss of both engines and available landing sites; and (3) the pilots' mishandling of the double engine failure checklist, causing the engine cores to stop rotating and resulting in the core lock engine condition.
Factors contributing to this accident included: (1) the core lock engine condition, which made it impossible to restart at least one engine, and (2) the airplane flight manuals not providing clear instructions to pilots on the importance of maintaining a minimum airspeed to keep the engine cores rotating.
Accidents also occur when the "density altitude"—a combination of temperature and atmospheric pressure at a specific location—becomes too high. On a hot day at high altitude, certain aircraft types struggle to climb. They may lift off the ground but fail to gain altitude, leading to a crash due to a lack of runway or an attempt to return to the airport that results in a stall. An example of this is detailed in WPR12LA283.
Helicopters face a similar issue. Helicopter crews calculate the "power available" at a given pressure altitude and temperature, then compare it to the "power required" under those same conditions. The power required differs for hovering "in ground effect" (IGE, with the advantage of a level surface that assists the rotor system) and "out of ground effect" (OGE, where the rotor system supports the full weight of the aircraft).
It's somewhat unnerving to take off from a location like a helipad on top of a building, transitioning from hovering in ground effect to suddenly finding yourself in an OGE situation, unable to maintain hover as you move out over the roof. This is why helicopter pilots prioritize establishing a positive rate of climb as quickly as possible in such environments—once moving forward at around 15 to 20 knots, the airflow through the rotor system provides additional "translational" lift.
It also feels uncomfortable to dip below the translational lift airspeed too high above the ground and suddenly find yourself in a power deficit—perhaps you have IGE power but lack OGE power. In such situations, you may not have enough power to cushion your landing, and instead of flying, you essentially plummet. (Any Monty Python fans?)
For a deeper understanding of the aerodynamics at play when aircraft fly too high, I recommend checking out the responses to the question, "What happens to aircraft that depart controlled flight at the coffin corner?"
This post originally appeared on Quora. Click here to view.
