Page 20 - Volume 12 Number 12

Figure 1: The RNAV (GPS) Z Rwy 17 at Montrose Regional Airport (KMTJ) in Colorado.
adventurers recently made their way to the site and actually found what was thought to be the cockpit voice recorder. However, no usable data has yet been retrieved. Officially, no cause has been found for the premature descent, so what I am about to write has no basis except hearsay from a King Air pilot I trained in the late ’80s.
This fellow was a rather senior pilot at Eastern while it was still in operation. He had personally flown this route often. Notice the date of the accident – New Year’s Day. He told me that the senior crews had bid that time off because of the holidays. According to him, the crew on this fateful day were new to South American flying. It was standard practice, he said, in this non-radar environment, to be cleared to 16,000 feet by the La Paz controllers when radio contact was first established. Yes, there was no conflicting traffic and ATC was indeed permitting you to descend to this lower altitude. But – and it is a huge “but!” – you cannot go down to that altitude now! The en route IFR chart clearly showed that you were still on a segment with an MEA of 21,000 feet! It was only after that segment had been passed that the MEA did permit continued descent to the assigned 16,000 feet MSL.
Just because you can, doesn’t mean you should! Here is a case where ATC gave permission for the descent yet there was another, overriding, constraint that would
correctly force the descent to be delayed, to be in compliance with the MEAs. According to the fellow who told me his theory as to the accident’s cause, receiving clearance to this unsafe-at-the-time altitude was almost universal practice by La Paz ATC.
Take a moment to examine the Instrument Approach Procedure in Figure 1, the RNAV (GPS) Z Rwy 17 at KMTJ, Montrose Regional Airport in Colorado. Imagine that you are approaching from the east, proceeding directtotheGEJYU IAF,60milesout, currently maintaining FL220, in radar contact. Denver Center: “King Air XXXX, descend at pilot’s discretion so as to cross GEJYU at or above 10,000 feet, cleared for the RNAV (GPS) Zulu Runway 17 approach to Montrose.”
At what distance from GEJYU would you begin your descent?
If your King Air has an autopilot system that supports VNAV, many pilots would dial in 10,000 feet for the altitude at the fix, use the default three-degree descent angle, and watch the magic happen.
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18 • KING AIR MAGAZINE
DECEMBER 2018