Tips and Tricks #30
Missed Approaches

Keith Thomassen, PhD, CFII
www.avionicswest.com

Anytime you do an IFR approach there is the possibility of having to do the missed approach (ma). Having to "go missed" can be stressful, particularly if you’re still in the clouds at the missed approach point (map). Being well prepared and knowing exactly what to do and when to do it will reduce that stress, so let’s review the various issues involved in executing a missed approach.

Just before entering the terminal phase of the flight, (30nm distance from the airport), you will review the approach, including the missed approach procedure. In addition to memorizing the final approach course direction, step-downs and minimums, you should look at each leg of the missed approach procedure, with particular attention to the first one, and understand them (more later). On the final approach leg (after the faf) think about the sequence of pitch, power, gear and flaps that you need to do at the map should it be necessary to do so. Mental preparation is everything – expect to miss, and not to land.

Variables in this procedure include the particular GPS navigator and autopilot you have. The FAA dictates that leg sequencing be interrupted at the map, requiring pilot intervention at this very inconvenient time. An exception is that the GNS 480, which was WAAS certified before all other navigators, escaped that requirement and sequencing to the ma legs is automatic. With the GNS 430W/530W and the G1000W the suspend light comes on at the map so you must push the SUSP button to make the first ma leg active. This is when you need to increase pitch and power, then raise the gear and flaps, but you should at least pitch up and add power before sequencing, particularly if you are at 200ft minimums and still in the clag. First things first.

On a Chelton, tiles for Miss and Arm appear, the first allowing you to execute the missed at that time, the second to remove the suspension that would otherwise appear when the map is reached. Arming the ma removes the suspension and continues sequencing after the map. As shown in Figure 1, the Avidyne (440/540) shows an “Enable Missed” tile that appears at the faf, allowing you to arm the ma legs early when not so busy. The GTN 6xx/7xx present touch screen tiles on reaching the map. The point here is that (except for the 480) you need to intervene to sequence to the ma legs, and you need to know how your specific navigator works in that regard.

Figure 1

Figure 1. On the Avidyne 540 screen (left), an “Enable Missed” tile appears on reaching the faf, while the “Activate GPS Missed Approach” tile appears (right) on a Garmin Touchscreen at the “map”. Note the SUSP light on the Garmin; The Avidyne unit does not have a SUSP tile or light.

 

If you want to start the missed early you can always activate the first ma leg at any time by selecting it in the flight plan. You can also do that with the “Arm” tile on a Chelton, or go to the flight plan (touch the approach tile) or procedure page in the GTN’s and “Activate Missed Approach” as shown in Figure 2.

Figure 2

Figure 2. Activating the missed in the Garmin Touchscreens before arriving at the “map”, from the flight plan page (left) by first touching the Approach banner, or from the Procedures page (right).

If this was a coupled approach, sequencing to the missed and having the autopilot fly it can be helpful at this busy time. I’ll assume you have a go around (GA) button in conjunction with your autopilot, but without it you disengage the AP mode at the map and engage the FD mode if you have it to follow commands from the ma legs. After establishing the initial climb choose new AP modes.

The recent GFC 500/600 digital autopilots from Garmin have a GA switch that commands a pitch up to a value specific to your aircraft, keeps the wings level, and does not disconnect the autopilot. After pushing the GA button you need to select a lateral mode such as NAV or HDG, the former to track the first ma leg, the second if ATC gives you a vector. If you don’t like the pitch angle and want to get out of GA mode, select another pitch mode (VS or IAS) or use the up/down scroll to change pitch.

If you have the S-TEC 3100 digital autopilot, the manual states that pressing the GA button does the following things simultaneously; disengage the autopilot, engage the flight director, engage roll mode with wings level, engage pitch mode appropriate to your aircraft, and cancel any armed pitch and roll mode and target altitude. Since each autopilot is different, refer to your manual for the recommended go around procedure.

Once on the missed, you’ll switch from Tower back to Approach, and you’ll be asked for your intentions. You have three options; try the approach again, do the missed to the hold, or proceed to your Alternate. If the weather at your destination was forecast, 1 hr before and after your ETA, to have ceilings better than 2000’ AGL with 3 statute miles visibility (the 1-2-3 rule), you won’t need one. But if you do need an Alternate the weather at there must be 600-2 if there is a precision approach, and 800-2 if the approaches are not precision. You’re also required to have fuel at cruise power to get you to your destination and then the alternate with a 45 min reserve. ATC will not know about your Alternate unless you put it in the remarks on your flight plan.

If you don’t want to try the approach again, the safe alternative is to do the missed to the hold. There, you will have the time to reorient your thinking and create a new flight plan to the alternate. While in the hold you can declare your intentions and get a further clearance and add those legs to your existing flight plan. So let’s discuss flying the missed to the hold.

First, be aware that many of the ma flight legs may be unusual for you. For example, they may begin with a heading to an altitude (VA leg), sequencing to a heading to an intercept (VI leg), onto a course to a fix (CF leg). If you have a GNS 430W/530W you will not see these first two heading legs, since they can't create any of the 5 heading legs (the other 3 being headings to a radial, DME distance, or manual termination), The first leg might instead be a fixed course (instead of heading) to an altiitude (CA leg), which provides analog deviation signals to your CDI and digital roll commands to the autopiloit. Will these legs sequence automatically?

It depends on your navigator. Does it know when you reach the end of each of these legs? To sequence from the VA leg it needs to know your baro-corrected altitude, so if the GPS is not fed this signal it will not sequence and you will have to force sequencing (Un-Suspend) at the specified altitude. Knowing if you’ve reached the intercept of the CF leg depends on the software built into your navigator. Some can do this (including the GTN 6xx/7xx) and some can’t. Also, these first two legs are heading legs, so there must be a magnetometer to let the GPS know your heading, and the software must be able to compare it to the desired heading and create a roll command to correct course. All legs ending in a fix will sequence, so the third leg sequences on every GPS.

Figure 3 (left) shows the ma legs for the ILS 34L into Sacramento Metro airport, which has 224’ minimums. The legs for this ma are the 3 legs described above. The VA leg, on runway heading (348°),

Figure 3

Figure 3. The missed approach legs for the ILS 34L at KSMF (left screen). The first VA leg is on the runway heading up to 500’, then the VI leg on a 320° heading that intercepts the 333° course (CF leg) to the GRIME intersection, where you will hold at 2000’ on that inbound heading. The approach to the Alternate at Redding, KRDD is on the right screen. Note that while on the missed approach legs to KSMF, this approach can be added to the existing flight plan, after the hold at GRIME. It can either be loaded or activated (don’t do that yet).

is followed by a 320° heading leg to intercept the 333° course to GRIME. So, after pushing the GA button, establish the climb then choose a lateral mode on the autopilot to follow these legs. Only roll commands (no CDI deviations) are issued from the first two legs, so you need an autopilot that can track in GPSS mode. With an analog autopilot in HDG mode and a GPSS convertor you can do that. Or, the above two digital autopilots track these roll commands in NAV mode. If you have altitude preselect on the autopilot, set it to 2000’ and it will level off there.

Now, in the hold at GRIME, we alert ATC to our intention to go to our Alternate at KRDD requesting the ILS 34 there. The GTN’s have is a unique feature that allows you to add a second procedure to the flight plan, but only when you are on one of the ma legs of the first approach. So go to the Procedures page, choose Approach, and select KRDD, ILS 34, and the RBL transition in the 3 boxes (right screen in Figure 3). These are added after GRIME in the flight plan as shown in Figure 4. Request the routing in this plan, D-> RBL followed by the ILS. If given a different clearance while in the hold ask ATC to standby, load the route, then comply.

Figure 4

Figure 4. The ILS 34 at our Alternate, KRDD, loaded into our flight plan after the hold at GRIME. Not that the missed on this approach has the same 3 leg types, a VA to 1100’, a 090° VI leg to intercept the 044° CF leg to ITMOR.

A missed approach can be stressful, but preparation and experience can ease that stress. Practice makes perfect, so when next you take an approach training flight, be sure to do the ma on each one. Carry these all the way to the hold, then practice adding another approach or route to another airport.

 

Home