Page 22 - Volume 12 Number 12

Figure 3: The RNAV (GPS) RWY 36 approach to Polson airport (8S1) in Montana.
while reviewing this approach. Receiving that same clearance, the tendency would be to actually cross NICQE at the 11,000 feet altitude the controller stated, rather than taking advantage of the “at or above” clause (31,000 down to 11,000; 20K to lose, 20 X 3 = 60 + 10% = about 70 miles). So, we would have been premature in our ideal descent profile by 20 miles. Dangerous? No. Big mistake? No. But not the most efficient or comfortable method, in my opinion.
Figure 3 is the RNAV (GPS) RWY 36 approach to Polson Airport in Montana. To be ready at 6,400 feet at or before DODSE, the FAF: (A) at what altitude would you like to cross ARLEE on your way to the CABLI IAF? (B) Would a standard three-degree descent angle keep you at or above the appropriate MEAs for the various legs of the transition?
The answer to (A) should be near 15,000 feet; and (B) is “yes.”
Lastly, take a look at Figure 4, the RNAV (GPS)-B approach to Sandpoint, Idaho. Same questions: (A) At what altitude would you like at the CESIG IAF? (B) Will your three-degree glidepath to 4,900 feet at FINTA, the FAF, keep you above the various MEAs?
The answer to (A) should be near 12,000 feet; and (B) is “yes.”
Do you grasp the point that I am trying to make? Be situationally aware in three dimensions and optimize your descent profiles when ATC permits. Just because you can descend to a lower altitude when ATC provides the clearance, doesn’t mean that you should start down immediately. Yes, of course, if there is no “at pilot’s discretion” included in the descent clearance, then you must start down without delay. However, I rarely use a three-degree descent angle in this case. If I aim for 1,000 fpm, ATC rarely complains.
All of the approach examples that I have used here came from approaches that we actually flew
in the C90A that I manage and fly out of the Phoenix area. The owner organized a six-day trip to various great locations in the Northwest and I was honored to be one of the crew. We were on the road from Oct. 5-10, 2018. Take a look on FlightAware if you wish to see our tracks: N3190S. I realize that those of you based on the East Coast would be rather surprised to receive so many “at pilot’s discretion” descent clearances.
20 • KING AIR MAGAZINE
DECEMBER 2018