Chart Wise: Flagstaff ILS/LOC Runway 21

Even the simplest instrument approach can present challenges to pilots who don’t plan ahead, but in this month’s chart, the ILS Runway 21 at Flagstaff Pulliam Airport, Arizona (FLG), pilots will encounter some issues unique to flying an approach into an airport with an elevation in excess of 7,000 feet—7,003 feet to be exact. This procedure demands careful consideration of aircraft performance limitations, especially in warmer months when density altitudes can climb toward the stratosphere. In winter, higher altitudes add the risk of icing.

A. Intercept Altitudes Because Flagstaff is located some 130 miles northeast of Phoenix, from which it derives some of its approach-control services, ­radar following may or may not be available ­depending upon the time of the day. This translates into pilots needing to be ready to fly the entire approach on their own.

During normal airport business hours, 0600-2200 local time, Phoenix runs the approach and departure services and can often track aircraft on radar down to ­nearly the surface depending upon the altitude and direction of flight. In the middle of the night, however, when Flagstaff’s local tower is closed, Albuquerque Center picks up the arrival and departure services and is limited in how low an altitude their radar will paint an aircraft target.

To begin the procedure, pilots can ­establish themselves on the initial approach segment using either the VOR at FLG and a feeder route to a procedure turn or out to the CALGU intersection. They could also use an IFR GPS to navigate to CALGU intersection. In either case, a minimum altitude of 12,300 feet is required until established on the inbound localizer and within 10 nm of the FIMAL waypoint, where descent to the lower 10,200 feet final approach fix crossing altitude is allowed. The procedure allows a descent to 10,500 feet between CALGU and ZAMAB intersection.

B. Required DME Does Not Come From the ILS Approach notes explain DME is required. Importantly, they also explain the aircraft must be able to simultaneously receive a signal from the FLG VOR, the actual DME source and the inbound ILS course (IFLG). IFR GPS-equipped aircraft could of course substitute that system to receive the ­required information.

C. MAP Won't Be Found at Zero DME Since the DME for the missed approach point is generated from the FLG VOR, which is not located at the runway end, pilots should not expect to see the DME count down to zero to indicate the MAP. The miss actually ­begins at 0.9 DME when flying this as a LOC approach, or if they were to reach that point before descending to the DH when flying the approach as an ILS.

Learn more about specific approaches: Chart Wise

D. Not Perfectly Aligned with the Runway The "final approach course is offset by 3 ­degrees," meaning the procedure ­actually lines up the aircraft just to the left of the ­centerline. The high terrain depicted to the west of the approach path is the likely cause and also a reason not to stray off course when flying outbound or inbound.

E. Warm Up Those Hand-Flying Skills Another note demands, "Autopilot coupled approach not authorized below 7,640 feet MSL." Coordinating this with the DH on the approach, 7,258 feet, means the pilot must disengage a coupled autopilot before ­reaching 7,640 feet and hand-fly the ­aircraft to minimums. This effort prepares the ­pilot to more quickly transition to a missed ­approach if needed, which would require a climb to 7,500 feet and a left turn away from terrain to the west.

F. Some Local Knowledge Can Be Useful Pilots flying nonturbocharged aircraft on an IFR flight plan to FLG when the ­weather is relatively good VFR below the clouds might consider not shooting an approach at all after first asking ATC for the minimum ­vectoring altitude in the area. That might safely put an aircraft beneath the bases and allow for a visual approach. Some local pilots also use a “contact approach” to fly up the valley from Sedona when Flagstaff is reporting good weather. This option ­allows pilots pick their IFR clearance back up should the weather change along the way. In either case, these options only apply when weather beneath high clouds bases includes good visibility.