GET SET, GO!

 

This is the last of three parts on pre-approach setup. As explained in the first installment, most IFR pilots lean on some form of mental checklist to assure they cover all the necessary bases as they prepare for approach clearance. Mine is AHARMMMS: Atis, Heading, Altitude, Radios, Markers, Minimums, Missed, Slow. So far, I've toppled the first four; still to go: Markers, Minimums, Missed and Slow. For reference purposes, I've used a slightly altered ILS approach chart for John Wayne airport (SNA) throughout the series.

MARKERS
Of all the checklist items, this is the only one that is truly optional: your planned approach either uses beacons or it doesn't. If, like the SNA ILS, it does, don't take your on-board equipment for granted. Check that the receiver is turned on–some have switches–that the audio is directed where you want–speaker or headphones, and that there is electricity to the unit(unfortunately, there is no way to perform a real receiver function check: the "test" button only verifies that the bulbs light up). Finally, the AIM recommends using the "low" setting on receivers equipped with a selective sensitivity feature.

MINIMUMS
Like Radios, this item tends to be complex. For some pilots, "minimums" triggers only a quick glance at minimum visibility and DH or MDA, as appropriate. However, a minimums check should be much more: a review of all step-down altitudes, a check of the required minimum visibility, and deliberate consideration of how you will go about determining if flight visibility actually meets the minimum at conclusion of the approach.

This last suggestion will be new to a predictable number of readers. Few instrument CFIs put sufficient emphasis on flight visibility and the planning needed to make quick decisions about it at the end of the approach. It's an understandable failing–most IFR training is done under the hood in VFR conditions, making minimum visibility an abstraction for the majority of newly rated graduates. Understandable, but also potentially very dangerous. Not surprisingly, the termination of the approach is the stage of IFR flight most prone to fatal mistakes. In other words, this is where confusion and slow decision making can kill you.

FLIGHT VISIBILITY
If you arrive at or close to the missed approach point (MAP) still solidly in the clouds, decisions about visibility are easy: give up the approach and start climbing. Far more difficult is the quagmire created by partial visibility and dimly seen terrain. Remember, reported ground visibility may have little relevance to what actually faces you as you begin to see surface details. Is that the runway? How much of it can I see? Is the visibility good enough to land? Just how far is 1/2 mile, 3/4 mile, 2400 RVR, 5000?

Unless you have memorized some local landmarks, the three most reliable clues to unravel questions about visibility are distance of the MAP from the threshold (most useful on ILS approaches), the length of the approach light system (ALS), and the length of the runway itself. Here are a few examples.

Precision Approaches: On an ILS, the single best clue for determining visibility is location of the MAP. The location is determined exclusively by the glideslope (GS) angle. John Wayne's GS is a standard 3°, which works out to a gradient of 20:1 and places the MAP (after just a little bit of math) precisely 3500' from the threshold. The standard minimum visibility for a Category 1 ILS is 1/2 mile, and since 3500' is well over that, it follows that if you can see the threshold at or before MAP on an ILS approach, you have the required visibility. I think this is one of the nicest features of the approach type.

When visibility is very poor and the runway still not in view as you arrive at the MAP, the regulations permit an additional 100' descent below DH, provided you have the ALS in sight. In addition to authorizing this descent, the ALS also provides a useful guide to visibility. Here is how it can work. On precision approach runways, the light arrays vary from 2400' to 3000' in length. Continuing to use SNA as an example, the ALS is a MALSR, 2400' long. This means the end of the array is a little more than 1000' from the MAP–if you can see any portion of it from that point, you have at least 1000' visibility. You need 1/2 mile, only 1600' more, a further calculation you may find facilitated using the yardstick provided by the ALS.

Two conclusions should stand out at this point. One, continuing an approach when the visibility is very poor is not for the faint of heart. Two, it is also not for pilots who have failed to give the issues considerable thought before starting the approach. Although the AHARMMMS checklist can serve to trigger considerations about minimums, it can't substitute for genuine understanding.

Non Precision Approaches: In the absence of a glide slope, neither of the methods presented above are much use in determining flight visibility. For one thing, the minimum is probably going to be higher than 1/2 mile. For another, of course, there is no DH. By far the most useful tool on a non precision procedure is therefore the yardstick provided by runway itself. As an example, the instrument runway at John Wayne is 5800' long–more than a statute mile and immensely helpful in determining just how far you can really see. And once again, this data is no use at all if you haven't already familiarized yourself with it by the time you come to make the actual decisions.

MISSED
We have come to the last of the three M's–review of the missed approach procedure. Unless the approach you are making is one you fly often, it is unlikely–and unnecessary–you will have the entire procedure memorized. However, certain details must be clear from the start: Does the missed begin with a turn or a straight ahead portion (the plan view is the quickest source of this information)? Will you need to tune a new navaid, or can you use one already selected? And, finally, where does the missed actually start? The last M is an ideal reminder to pre-set a timer, verify a DME frequency, set an OBS, or recheck DH.

SLOW
We all aspire, I imagine, to fly airplanes that cruise at airspeeds faster than wanted on the approach. This means slowing down as you prepare for arrival. One easy way to drive yourself crazy in the instrument environment is to forget to do this until it is too late. By too late, I mean a point where you have already lowered the nose to begin the approach descent and find you cannot slow down without making drastic power reductions that promise earlier than necessary engine overhaul.

The need to slow underlines the importance of starting and completing the entire AHARMMMS checklist early–at least twenty miles out in training types, further in faster aircraft. If you choose to start later, you risk being rushed and forgetting items —precisely what you were attempting to avoid by using the checklist in the first place.

BUT WAIT. THERE"S MORE…
Finally, with all pre-approach items done, it still isn't time to relax. Most pilots have at least one more checklist waiting in the wings at this stage: 6 (or however many you use) Ts. That checklist was discussed in detail in this space in past columns (IFR Refresher, April-May 2001) and contains all the items you are likely to want to check off as you pass the outer marker or final approach fix, as appropriate. In many cases, these items require some pre-setup activity, so conclusion of AHARMMMS is an ideal place to get started on a "rehearsal" of the Ts–a check to make sure the required data and actions are ready to proceed smoothly.

THAT"S IT
The end. It can sometimes seem to take as long to complete AHARMMMS in the air as it did to explain it here on the ground. Unfortunately, there really aren't any short cuts–every item requires attention on every approach. If you are accustomed to flying only a couple of approaches–an easy pattern for some pilots to fall into–you may take many of the actions for granted, doing them almost without thought. If so, beware of unfamiliar procedures when you do fly further from home. The best possible preflight preparation for an unfamiliar instrument approach is to thoroughly review each approach chart using the AHARMMMS checklist to alert you to the necessary setup items.

Next, the "6 Ts."