Three Ways to Start an Instrument Approach: Vectors, IAF and Intermediate Fix (IF)

A friend lamented on Facebook that the NDB procedure at the airport where he learned to fly is no longer available. He added  “For some reason it makes me a little sad.” I’m guessing his sadness had more to do with his feelings about learning to fly at that airport, than it did about flying an NDB approach. Or perhaps he was reminiscing about the pride he felt in mastering the NDB approach.

I used to enjoy the intellectual challenge of flying an NDB approach and the even greater challenge of teaching others to master it. But no more. There are no NDB approaches left in the S.F. Bay area where I teach and I say “good riddance.”

The approaches were inaccurate and difficult to fly and former Secretary of Commerce Ron Brown was killed when U.S. Air Force pilots failed to correctly fly a rare “dual NDB” approach. I’m much prefer to see pilots expend their intellectual horsepower on mastering flying IFR approaches with modern GPS receivers, which can be more work than learning NDB approaches, and staying up to date on rule changes.

One rule change that frequently causes confusion among pilots and controllers alike relates to the third way to fly an instrument approach. All instrument pilots know you can fly an approach with vectors or use pilot navigation to start at an IAF (initial approach fix). However there’s a third way that’s been around since 2006, but word about it has been slow to get out to pilots and even to a few controllers.

Pilots can now start an instrument approach, with some restrictions, by flying directly to the IF (intermediate fix). Just to remind those who may have forgotten, the initial segment of a typical instrument approach procedure starts at an IAF and ends at the IF. So typically the IF is the next fix after the IAF as you fly toward the airport.

You might be wondering, “What’s the big deal, why would I want to skip the IAF.” For many approaches it won’t matter, especially if the IAF is along your direction of travel toward the airport. But for some approaches it can save a few clicks on the Hobbs meter. For example, at my home airport of Palo Alto, Calif., the GPS 31 approach has two IAFs, but both are in the boonies and most pilots start the approach at DOCAL, the IF.

You’ll find the details about starting an approach at an IF in section 5-4-7(i) of the Aeronautical Information Manual (AIM), where it first appeared in 2006 (yes eight years ago!). However, you won’t read about it in the FAA’s Instrument Flying Handbook or even in the FAA Instrument Procedures Handbook, both of which are excellent publications.

The rule applies to all approach types, not just RNAV (GPS) approaches. Here’s the current text from the AIM:

ATC may clear aircraft that have filed an Advanced RNAV equipment suffix to the intermediate fix when clearing aircraft for an instrument approach procedure. ATC will take the following actions when clearing Advanced RNAV aircraft to the intermediate fix:

1. Provide radar monitoring to the intermediate fix.

2. Advise the pilot to expect clearance direct to the intermediate fix at least 5 miles from the fix.

NOTE – This is to allow the pilot to program the RNAV equipment to allow the aircraft to fly to the intermediate fix when cleared by ATC.

3. Assign an altitude to maintain until the intermediate fix.

4. Ensure the aircraft is on a course that will intercept the intermediate segment at an angle not greater than 90 degrees and is at an altitude that will permit normal descent from the intermediate fix to the final approach fix.

Here’s what it means to a typical GA pilot.

1) You need to be GPS equipped (which is the only practical way for most GA aircraft to be RNAV equipped). This let’s you find your way independently to the IF.

2) The controller might advise you that you’ll be starting the approach at the IF, but more typically, you’ll have already requested that of the controller.

3) You’ll be assigned an altitude to maintain until reaching the IF. Most likely you won’t be on a published segment of the approach until the IF, so you need to be assigned a safe altitude.

4) The controller cannot clear you directly to the IF until you’re in a position from which you can make a turn of less than 90 degrees to join the approach at the IF.

It’s the last part, making a turn of less than 90 degrees, where pilot and controller sometimes get confused. The idea is that the turn at the IF needs to be an easy one, much like turning left or right at the intersection of two streets. It can’t be a hairpin turn or resemble something like a U-Turn.

Think of it this way. If you were to draw a line on your chart at the IF that’s perpendicular to the intermediate segment, on one side of the line, the side farthest from the airport, you are allowed to fly directly to the IF, since the turn inbound is less than 90 degrees. If you’re on the other side of the line, the side closer to the airport, you can’t be cleared to the IF until after you’ve been vectored across the perpendicular line.

All of this presents some new challenges for pilots and controllers, especially if they’re unclear on the rule.