Five ILS Gotchas

Flying the ILS isnt rocket science, but there are a few mistakes pilots regularly make. Knowing what they are and how to prevent them can keep you out of the weeds.


How are your ILS approaches going? As the saying goes, it takes practice to make perfect, or even to keep current. The reward is the nice feeling and confidence boost received once you lock onto an actual-weather ILS approach, especially one you know from the beginning is going to turn out to be precise.

Of course, not everyone can get their approaches to work the way they want. Often, though, the reasons are well-known and, it should come as no surprise, so are the solutions. Lets review five of the basic problems pilots experience with the ILS and work on some solutions.


Before a pilot starts his ILS approach, there is considerable planning to accomplish for both the approach and the landing. The information used is what has been obtained during your preflight planning and weather briefings. Planning should include reviewing the surrounding terrain, hazards and the runway layout.

After ensuring you have the on-board equipment including current charts or data necessary to execute the approach, you also should determine which procedures you are likely to get and which, if any, you would be unable to shoot. Its also important to anticipate the type of landing you are most likely to use straight-in or circling.

Unfortunately, even if you have thought out the type of approach that you would like to use, you may not get it. It happens. So, if you want to be certain of a safe flight, youll need to do a little more homework. Be prepared to land on any runway that may be assigned to you at your destination. The terminal approach chart for the airfield of intended landing will show the airfield and runway layout, the type of approach lighting used and the obstructions.

Flying IFR into a strange airport, a pilot will want to be able to make the transition from instrument to visual flight as easy as possible. And this pilot will want to know in advance what are the minimum altitudes for straight-in and circling approaches. The field elevation, and the emergency safe altitude for the destination airfield, also are top priority information. If possible, it would be very useful to form a mental picture of the airfield layout, particularly the location of the buildings and any nearby obstructions.


While youre still at altitude and approaching the destination is the best time to plan the arrival, not when already getting vectors. This phase is when the pilot should already have the destination weather, the localizer and any other necessary avionics for the approach are tuned and the appropriate approach plate is retrieved. This also is when establishing a good mental picture of the traffic situation, any adverse weather and the airplanes position and relationship to the final approach fix must be done.

The pilot needs to know what the method of transition to the localizer final approach course will be. The transition gets the aircraft from the en route phase to the localizer course by radar vector, DME arc, transition fix, ADF, procedure turn, holding pattern, vectors or other maneuvers. Of course, its extremely important that the pilot know the relation to the inbound localizer course to the aircraft position. What is the angle that the aircraft is approaching the localizer course? What is the distance from the localizer course? The pilot needs to be able to anticipate what instrument indications to expect, and when to expect them. A careful study of the approach procedure can answer many of these questions.

Usually, youll be getting vectors to join the localizer at a point three to five miles outside the final approach fix. Early in the transition, the pilot needs to slow the aircraft to a speed allowing a safe transition from the en route environment to the approach and which considers other traffic. Ultimately, this speed is one which must allow the airplane to be slowed further, to the speed at which you want to shoot the approach. The pilot also needs to be aware of his intercept angle, as provided by vectors from ATC or via intermediate routing. To avoid overshooting the final, this heading should be between 30 and 45 degrees.

It goes without saying that a long, shaky intercept is to be avoided. Instead, what you want is a positive and smooth localizer intercept, followed by a precise turn to a heading that will lock you onto the localizer.

Whats next? The before-landing checklist needs to be accomplished, and the aircraft configuration modified as required. If the airplane isnt slowed up enough to get gear and flaps down, or somehow ends up on an impossible intercept angle, it will certainly result in a final approach course overshoot. From there, things rapidly can get worse. Attempting to get the airplane slowed down, while trying to capture the localizer, is the start of an unstabilized ILS approach. This is usually followed by an unsuccessful approach and being forced to execute the missed approach procedure.

During the transition phase, as much of the final checklist as can be managed is accomplished usually right up to flap and landing gear extension. Of course, at this point the pilot should be familiar with all the details on the approach plate, particularly the missed approach procedure. Its surprising how many pilots that I have seen on instrument currency rides, who are totally wiped out by ATC (or my) calling for a missed approach.

It happens in the real world of wet, stormy IFR, too.


The final approach is the most critical of the ILS procedure. It can be the easiest phase to fly if all the details have been addressed but it does call for the most precise flying.

Beyond the final approach fix, errors magnify, as pointed out earlier. The closer the aircraft comes to its decision height, the more the pilot must increase his instrument scan rate; the altimeter becomes very important, too. The single pilot needs to bring into his scan cycle a quick glance for the runway environment.

The most common mistake is overcorrecting: forgetting that when close-in to the runway threshold, deviations appearing large on the ILS localizer/glideslope instruments are really very small deviations. If the pilot thoroughly understands the system, plays it cool and doesnt panic, the approach can be successful.

But there is a caution. The glide-slope indications cant be ignored. From the final approach fix to the missed approach point, the pilot cant allow the aircraft to get below the glide path. This is the catastrophic zone.

The FAA criteria for designing instrument approaches doesnt allow for a lot of errors. Obstacle clearance at a point located 3000 feet from touchdown the glideslope can be as low as 92 feet from obstacles. So, if you flunked an instrument flight check because you were any amount below glideslope on final approach, you know why.


The first time a pilot on an ILS approach is involved with sneaking under the glideslope is almost always a situation where he or she is on an ILS final, approaching minimums. Hes close to decision height and suddenly there are patches of ground surface appearing intermittently in the clouds below.

An instant later, the strobes are visible. He drops below the glide path, and finds the runway straight ahead. Later, thinking about it, the pilot realizes that if he had remained on glideslope, descending to decision height (DH) would have led to executing a missed approach.

This tempts the pilot further for the next ILS at another time. On the next gamble, he descends a little bit more below the glideslope and it works again. In fact, it works a number of times. The best estimates seem to indicate that more-experienced pilots often professionals are involved in “ducking under” accidents than lower time instrument pilots.

The last few hundred feet of the approach requires the greatest amount of concentration and discipline. There are pressures. A commercial pilot and crew wants to get home on time, and they are tired they want to get the bird on the ground. They are not thinking “missed approach.”

This is where cheating on the glideslope eventually leads the risk-taking pilot to a disaster. Trees, wires, buildings and hills all suddenly are a split-second away.


There are a number of difficult points in any IFR approach, certainly, depending on the pilots experience level. The most difficult is undoubtedly the missed approach: Everything seems to be going well, the ILS approach is on greased rails, the approach lights are due any second and, then, whoa! The middle marker is flashing and sounding, but there is no runway environment in sight. What went wrong? Dont know, but now its missed-approach time.

Some keys to executing the missed approach:

Apply full takeoff power. Once the airplane has stopped descending, raise the landing gear and adjust the flaps to the en route climb configuration.

If there is a different frequency required for the miss, it should already be in standby. Hit the button and let ATC know your intentions.

Climb to the missed approach altitude. Proceed to the designated fix, or as directed by your approach clearance.

But, as long as the weather is decent and youve followed these suggestions, you shouldnt need to go missed, should you?

Ray Leis holds ATP, CFII, Commercial and glider certificates, and has served as a Designated Pilot Examiner.


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