Monday, May 19, 2014

Early turns on missed approaches; ILS MAPs

There you are flying down final (on any kind of approach) in real IMC, and something happens - the needle goes full deflection, you have an equipment problem, whatever - and you need to go missed. ATC isn't available, either due to RADAR or radio coverage, so you need to fly the published missed. Simple enough, we fly missed approaches all the time in training. You're on the ball and already had the missed all briefed and set up well before you reached the FAF. So it's a simple matter of flying it, right?

Many missed approaches have as a part of the instructions something like "climb to XXXX MSL then turn..." (in other words a delayed turn) because there's probably a good reason for the delay. Yes, it might be airspace, or traffic flow or ATC preference, which might not be your most significant concern when facing an emergency. Or it could very well be to avoid buildings, tower, or mountains, which obviously would be a very big concern! The problem is, when flying the procedure and looking at the chart, it may not be obvious which is the case. With the proliferation of tall antenna towers, you could have the same problem with antennas in Iowa that you'd have with mountains in Idaho.

So far so good. But where do you perform this turn? Regardless of the situation, you are expected to not perform any of the missed approach instructions until you reach the MAP. Of course, during training we almost always descend to the DA/MDA and decide to go missed when we're already at the MAP. Using the Burlington, Vermont ILS OR LOC/DME RWY 33 as an example:

Note the missed approach is "climb to 1200 then climbing left turn to 2800 direct  BTV VOR/DME". Let's say you're somewhere between JIDSO and KOTDE and find yourself well below glideslope and off course. You are clearly well behind the airplane. Maybe you're already down around 1700 before KOTDE. You (wisely) decide to go missed. Since the missed approach instructions say "climb to 1200 then..." and you're already above 1200, you can turn direct the VOR, right? No! Remember, all missed approach instructions presume you start the missed approach AT the MAP. There is some allowance for timing errors and such, but not this much.

From the Instrument Procedures Handbook, page 5-33, "When a missed approach is executed prior to reaching the MAP, the pilot is required to continue along the final approach course, at an altitude above the DA, DH, or MDA, until reaching the MAP before making any turns. If a turn is initiated prior to the MAP, obstacle clearance is not guaranteed. It is appropriate after passing the FAF, and recommended, where there aren't any climb restrictions, to begin a climb to the missed approach altitude without waiting to arrive at the MAP."

The Aeronautical Information Manual, section 5-4-21b and h, and the Instrument Flying Handbook page 10-21 have essentially the same information.

Looking at the previous example, you can see there is some terrain between you and the VOR if you were to make that left turn before KOTDE. How high is this terrain? I don't know, and you probably don't either. The one clue we do have is that the shading of the contours implies it's at least 1000 MSL, but less than 2000 MSL. That could put us in a pretty dangerous situation if we're starting at 1700!

So we need to wait until the MAP to turn. How do we know where that is? On a non-precision approach, of course, the MAP is often defined by crossing the VOR or NDB, a DME fix, an intersection, or lastly, timing from the FAF. However, the MAP on an ILS is defined as when you reach Decision Altitude on glideslope. If you are having some kind of situation (emergency or otherwise) requiring a missed approach, though, you don't want to keep descending. Much safer to get further away from the ground, so you level off and start to climb. Due to this climb, however, you can no longer identify the ILS MAP since you're well above DA.

Can you use the Localizer MAP? Probably the best idea if you're set up for it. In the BTV example, you've probably been using DME all along the procedure, so the best solution is to just climb straight ahead, wait until you reach the LOC MAP (0.2 DME past the VOR) then begin the turn.

If, however, the LOC MAP is identified by timing, did you start your timer at the FAF? Many people forget or neglect to do that when flying ILS procedures since it's normally not needed. If you didn't start your timer, then you might be out of luck as far as identifying the MAP goes.

Notice the next example, Grand Junction, Colorado, ILS OR LOC RWY 11. Part of the reason for the straight-ahead climb here is probably to gain some altitude first before turning toward the mountain that the VOR sits atop. If you turn before the MAP here, do you have enough distance to climb before you get to the rocks? (How's your high altitude climb performance? Any downdrafts to consider?) Let alone you're supposed to intercept the R-085 inbound, this could make for some confusing maneuvering.

But at least that one has a timing table. How about at Reno, Nevada, the ILS RWY 16R?

No timing table or even a LOC MAP, since it doesn't even have Localizer minimums (that's a separate chart). Now, the climb-to altitude is only a couple hundred feet above the DA (which is very high in itself), but you still wouldn't know when you were at the MAP and therefore when exactly to turn. In addition, since the DA is so high, the MAP is actually about 6 nm prior to the runway!

Any time you turn before the MAP you are stepping into uncharted (hah!) territory. Most of the time it would probably work out okay, but do you want to take that chance?

So what can you do? First, a good approach briefing is critical, and I recommend starting your clock at the FAF on every approach just as a habit. But if you didn't do that, then you're really in an emergency situation - you've lost situational awareness and don't know your true position. First, of course, climb! Then, ultimately, it's about making a "best guess" as to where the MAP is. If you have a portable GPS up and running, use that. If you can get a DME source, use that. Maybe there's a VOR on the field that, while not used on the procedure, would give you a TO/FROM flip when you cross over it and at least tell you where you are. If none of these are available, then consider climbing up to the MSA before turning - you know that will provide obstacle clearance for a 25nm radius. And in fact, it provides at least 1000 feet of obstacle clearance - an extra cushion when it's really needed.

Sometimes approach planning can take a lot more thought than normal, and identifying the MAP on an ILS can be one of those situations. As always, the best time to figure this out is on the ground before takeoff. Fly safe!

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