IFR Fix: 'Would you like a lower altitude?'

July 13, 2012

Ifr Fix

Nothing is more fun after a serious spell of IFR flights packed with clouds and approaches than some good old recreational aviation on a summer day. Even on a VFR cross-country, it’s likely that we’ll find you cruising along, enjoying the scenery down there with the floatplanes and the classics.

Many pilots fly at their highest altitudes under IFR, necessitated by minimum en route altitudes delivering at least 1,000 feet of obstacle clearance (2,000 feet in designated mountainous areas), or motivated by the desire to top clouds or catch tailwinds.

You can look up your aircraft’s service ceiling in the pilot’s operating handbook. What about the pilot’s ‘service ceiling?’

When a Boeing 737 first officer got that tingly feeling after takeoff, it wasn’t from giddiness about the joys of jet travel.

“Passing through around 13,000 feet, I began to feel tingling in my arms and legs. Having experienced symptoms of hypoxia before, I immediately donned my O2 mask and started a descent. I told the Captain we were not pressurizing and to get his mask on, within a few seconds the tingling was gone,” the FO said in an Aviation Safety Reporting System narrative, one of numerous cases citing oxygen-system or pressurization glitches.

Not every pilot is so self-aware – a known hazard of hypoxia.

On May 17, 2011, a Denver Center controller perceived that a Cirrus SR22 pilot flying at 17,000 feet was becoming incoherent on the radio. “I think you might be experiencing some hypoxia. Would you like a lower altitude?” he calmly asked the pilot, while working other aircraft on the busy frequency.

During the approximately 41-minute FAA recording of the incident, the pilot becomes incapacitated, and a passenger tries to comply with instructions from the ground and a nearby flight crew. High terrain is a constant constraint on the controller’s efforts to guide the flight lower, to oxygen-rich air. Below 10,000 feet the pilot apparently recovers, eventually landing the Cirrus in Farmington, N.M., elevation 5,500 feet msl, to general relief.

What’s your body’s service ceiling? Lower than its current cabin altitude?

The answer may not mirror FAA rules addressing oxygen use during flight. That’s one of many insights to be gleaned from the Air Safety Institute’s 10 -question hypoxia safety quiz.

Take the quiz. Plan better. Breathe easier.