IFR Fix: 'Random impromptu routings'

November 1, 2013

Which word in the instrument pilot’s vocabulary is so prized that it commands its own button on navigation units? (Hint: Its symbol is the letter D bisected by an arrow.)

Nothing beats hearing "direct" in a route clearance, or failing that, an authorization to jump ahead a fix or two later on.

So, what keeps you clear of trees and rooftops when navigating direct?

Beyond your navigation charts, ATC has resources including a minimum vectoring altitude that "meets IFR obstacle clearance criteria. It may be lower than the published MEA along an airway or J-route segment."

Two caveats: An MVA "may be utilized for radar vectoring only upon the controller’s determination that an adequate radar return is being received from the aircraft being controlled." MVA charts are normally available to controllers, but not to pilots.

Recently updated Aeronautical Information Manual Section 5-1-8 notes the importance of radar monitoring when an RNAV aircraft proceeds via "random impromptu routings"—those that create "a direct course initiated by ATC or requested by the pilot during flight. Aircraft are cleared from their present position to a NAVAID, waypoint, fix, or airport."  

GPS systems with terrain warning capabilities add margin in case the eyes on the radar scope ever blink.

They blinked, said the National Transportation Safety Board, on Oct. 28, 2012, after a Piper PA-32R-300 single departed Tennessee’s Gatlinburg-Pigeon Forge airport toward hilly terrain.

A terrain alert caused the 502-hour private pilot—who had accepted a vector to an enroute fix rather than fly to a VOR as filed—to query ATC. However, “he received no reply. Subsequently the GPS provided an obstacle warning, and the pilot observed a rooftop and trees through the clouds. He pitched up and banked the airplane in order to clear the obstacles, however, the underside of the airplane impacted several trees,” said the NTSB, summarizing the minor-injury accident.

The report noted that the controller had not made "the required radar identification," and "had not issued the pilot a safety alert, even though the airplane was maneuvering below the FAA charted minimum vectoring altitude." It discussed the controller’s focus on unrelated tasks, criticizing the FAA for having controllers on radar operational duty supervising other controllers. And it described a "culture of non-compliance with required procedures" at the facility.

All pilots jump at a chance to proceed direct. Make sure it’s not a leap of faith.

Dan Namowitz

Dan Namowitz | Aviation Writer

Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.