IFR Fix: 'Deviate as necessary'

April 8, 2014

The clouds were angry, but the passenger was angrier. Bowing to the bluster, a Cessna 421 pilot tried to shoot a gap between cells, committing "the worst lapse of judgment in my life."

The pilot was flying four passengers from Perryville, Mo., northbound to Moline, Ill., when radar "showed two storm cells that appeared to be straight ahead and just south of Moline."

"It looked as though I could fly between the cells by deviating to the west," the pilot said in an Aviation Safety Reporting System narrative. Approach cleared the flight to deviate as necessary, but as the twin neared Moline, "the cells started to look worse on radar and appeared to form one large cell."

Galesburg was nearby. The pilot announced that the flight would land there. Three passengers "reluctantly agreed." The fourth "became very angry."

"It took me by surprise that he would react that way," the pilot reported. "I hadn’t been around people who act that way before."

Galesburg was in sight "when I had the worst lapse of judgment in my life and decided to press on to Moline in order to please that passenger." The flight spent the next 10 to 15 minutes flying "through turbulence like I had never imagined."

Gap-running is part of the chaos of violent weather. A pilot who uses onboard weather detection gear to take on more risk is missing the point of the safety edge it offers. Resources available to pilots, as well as ATC radar, may depict conditions several minutes old—of dubious worth against a thunderstorm that might develop at 6,000 feet per minute. (The time delay for ATC radar is discussed on page 2-11 of the Instrument Flying Handbook.)

The race was on when an Embraer 170 crew, cleared to deviate as necessary, followed other aircraft "traversing a break in the weather" about 80 miles wide, and closing in.

From 50 miles, the gap appeared 40 miles wide. "As we approached within 10 miles of the gap, ATC asked if we were going to make it through. At this point the gap had all but closed up, however we were close enough that any turn would have put us in areas of heavy radar returns,  i.e., we were committed."

An encounter with severe turbulence followed.

Convective weather is known as the maximum challenge for airmanship, but now add variables such as a scrambled ATC scenario, a closing gap, and a cabin distraction for the more complete picture of bad-weather flying.