Page 21 - Volume 12 Number 12

Without a VNAV computer, it might go something like this: “OK, I have 12,000 feet to lose from 22,000 down to 10,000, so I will need about 40 miles [(3 X 12) + 10%]. Since I am 60 miles out now, I’ll start down in about 20 miles.”
For this to work, the rate of descent must be about five times the ground speed (GS). In a C90A, for example, if our GS will be about 240 knots in the descent, I would initially target for a 1,200-fpm descent rate. (Most people prefer to take half of the GS and add an extra zero on the end ... which is the same as multiplying by five.)
But now consider another method, and a better one.
WIDRU, the FAF, is where our ducks need to be in their neat little row: 8,100 feet, Approach Flaps, Gear Down and 120 KIAS. Notice the GP angle of 3.00 degrees lurking on the right side of the profile view. Let’s extend that three-degree angle out to our IAF: 6.1 nm from WIDRU to BRUUK and another 10 nm from BRUUK to GEJYU, so about 16 miles total. I can comfortably lose 4,000 or even 5,000 feet in that distance: [(5 X 3) + 10%] = 16.5 nm. Therefore, I could be at 12,000 or even 13,000 feet at the IAF and make a very comfortable, normal descent so as to be all set at the FAF. If you want to get down to 8,100 feet a few miles outside of the FAF to have time to slow and configure, fine. One of the beautiful things about King Airs, however, is their ability to slow while descending on a three-degree angle. If you’d rather use that technique, join the crowd that includes me.
Using this last method, targeting the IAF at 12,000 feet instead of the allowable 10,000, I could delay my TOD (Top Of Descent) for six more miles. Fuel savings? A little. Staying high longer and thereby avoiding the lower altitude turbulence a bit longer? Probably. Going though icy clouds at a higher airspeed while descending with a low angle-of-attack rather than slogging along lower in level flight ... yes, I’d prefer that.
Take a look now at Figure 2, an approach to Runway 22 at Cody, Wyoming. You are coming in from the south in your G1000NXi-equipped 350, direct to NICQE, at FL310. You have told Center that you will be asking for this approach with the transition route from NICQE to HOZZR and Center has said to expect that.
If we add this procedure into our flight plan, we will see that 7,500 feet is already populated in the altitude field associated with the FAF, ELYPS – 7,500 will be in blue or cyan, designating a “true,” necessary, constraint. (“Blue is True; White sheds Light” ... thanks to FlyingLikeThePros on YouTube for that memory- jogger.) The VNAV computer, using the default three- degree angle – same as this approach, by the way – will now extend the glidepath all the way out to NICQE. Using our “three times the altitude to lose plus a cushion” rule of thumb, let’s predict what altitudes will be shown on the flight plan for the fixes outside of the FAF: 6.2 nm to DUSCA equates to about 2,000 feet. Thus, I would
DECEMBER 2018
Figure 2: An approach to Runway 22 at Yellowstone Regional airport (COD) in Cody, Wyoming.
expect to see a white altitude number close to 9,500 in the flight plan at DUSCA.
Another 7 nm back to HOZZR ... again a little over 2,000 feet, so let’s guess 11,700 feet there. Now continuing back to NICQE, 16.1 nm, means about 5,400 feet, so the reference altitude there would be about 17,000 feet.
What will be my flight plan’s TOD position then? Since I am currently at FL310 and want to cross NICQE at 17,000 (31,000 – 17,000 = 14,000 feet; 14 x 3 = 42 + 10% is about 46). So, I reckon the TOD will be not quite 50 nm away from NICQE.
It will be no surprise then to receive this clearance from Salt Lake City Center when about 15 miles or so from TOD: “King Air XXXX, descend at pilot’s discretion so as to cross NICQE at or above 11,000 feet. You are cleared for the RNAV (GPS) Runway 22 approach to the Yellowstone Regional Airport.” Ain’t technology great?! Monitor carefully, adjust power as needed, be configured no later than ELYPS, enjoy the magic.
Suppose you’re in a King Air without the VNAV capability and had not taken the time to “do the math”
KING AIR MAGAZINE • 19