Improper IFR

Thats the coldly clinical term the NTSB uses to describe a host of IFR sins eventually leading to wrecks. Most occur on non-precision approaches.


Even the casual student of why aircraft accidents happen knows that in a large percentage of them, weather is a factor. (Its about 15 percent.) Thats not to say weather caused the accident, just it was implicated as one link in the chain of events that led to the typical accident. When we think “weather,” icing, thunderstorms, low visibility and turbulence come to mind, as well they should.



But the NTSBs accident files reveal a particular subset of accidents in which pilots operating in flyable if challenging IMC prang perfectly good airplanes into terrain and obstacles for no apparent reason. The agency throws these into a grab bag category it blandly calls “improper IFR.” This catchall describes a narrow range of sins, but most of them relate to vertical rather than horizontal transgressions.

We read enough accident reports to confess a certain discouragement at the level of skill-or lack thereof-of the typical pilot in the U.S. But theres good news: The number of incidents of NTSB-reported improper IFR have declined markedly in recent years. The NTSB reported no accidents in this category between 2006 and 2009, but there were 47 between 1989 and 2005.

We suspect some of this is due to coding and reporting variations, for in reading reports at random, we see some that should clearly be improper IFR that are assigned to another cause. Its possible that we uncovered only a fraction of the total occurrences. Further, as flight activity has decreased, so has the incidence of instrument-related crashes. On the other hand, could it also be that in general, the pilot population is retaining a sharper IFR edge? Could it also be that advancing technology such as terrain warning gear and the wider availability of EFIS displays, with their improved situational awareness, are also having a positive effect? Theres no way to say, of course, because we have no data for accidents that didnt happen, much less why they didnt happen.

But we can distill some useful advice from the mishaps we did find. Some of these were not specifically coded as improper IFR; we simply knew of them from other research. For our definition, improper IFR means a published procedure wasnt followed, thus loss of control in IMC or VFR-into-IMC arent improper IFR.

High Lethality

Accidents classified as improper IFR are quite likely to involve fatalities. Of the 47 accidents, 32 or 68 percent were fatal to some or all of their occupants. Thats less surprising than the fact that more than 30 percent didnt involve fatalities, given that improper IFR accidents typically occur in a phase of flight in which the aircraft is flying at least at its approach speed, or is climbing out on a departure. These arent as benign as runway excursions or gear-up landings.

Some pilots and occupants walked away from wild rides through the tops of trees, along road sides and the rough stuff short of runways. One pilot returned to his homebase with wood embedded in the wing fasteners. Survivors often got a little damp, because improper IFR invariably occurs in real IMC, sometimes really snotty IMC.

There are themes and patterns in botched IFR operations but, frankly, we were somewhat surprised at what we found. Ducking under on an ILS, for example, and honest-to-goodness busted mins on an ILS were so infrequent that we would label them no factor. The same cant be said of non-precision approaches.

What MDA?

The leading culprit in improper IFR accidents is descending below the MDA on a non-precision approach after passing the final approach fix. Pilots argue about technique here-should you drive-and-dive and run out the clock, or set up a constant-angle descent to reach the missed approach point just as you reach MDA? Even before the advent of GPS approaches with LNAV guidance, the rapid descent to MDA to a timed (or DME) missed approach was hardly standard procedure for everyone.

Seventeen of the accidents we found involved pilots who simply descended right through the published MDA, either right after the fix or closer to the airport.

Unfortunately, as a pilot, you never know where the controlling obstacle is on a non-precision approach, although youre guaranteed at least 250 feet of baro-derived obstacle clearance once youre past the final approach fix. But with the slightest moment of inattention, that can shrink to zero.

Interestingly, although general aviation pilots may fly the most non-precision approaches by dint of operating into small airports which dont have an ILS, airline pilots are hardly immune from the hazards of descent below MDA.

On a gusty, stormy night in November of 1997, the crew of an American Airlines MD-83 narrowly averted disaster on a seldom-used VOR approach into Hartfords Bradley International. They deviated below MDA and impacted trees, debris from which all but snuffed the engines. The airplane managed to make it to the runway, but with significant damage. Stale altimetry data was mentioned in the report, but ultimately wasnt a factor. The pilots had simply deviated below MDA prematurely.

Although most NTSB reports lack the detail for us to know what the pilot was thinking, our guess is that MDA deviations occur for two reasons: Pilots just dont notice-that was the case for the crew at Hartford-or theyre trying to sneak below the clouds to get a glimpse of the runway to complete the landing. Instrument flying is all about discipline and thats what it takes to avoid looking out the window or windshield as you start to notice flashes of ground contact or, at night, ground lights.

The only right way to fly a non-precision approach-and this applies whether you dive and drive or fly a constant angle-is to keep your head inside on the gauges until you reach the published missed approach point. Then look outside and see what you see before continuing.

The advent of vertical guidance for near-precision GPS approaches may improve the overall safety of these procedures, but it doesnt change that fundamental equation.

Back It Up

We didnt find many improper IFR incidents that occur outside the final approach fix, on the intermediate segment. We would have expected that given the confusion over when to fly them and when not, botched procedure turns would pop up in the reports. But we found only one of those. We also found a couple of accidents where pilots missed the localizer intercept, or just couldnt track it and came to grief as a result. One bold pilot tried to fly the ILS in foggy Nantucket without benefit of a glideslope receiver, with predictable results.

From our previous accident research and that done by others, weve generally found that improper IFR is more often a thing of vertical dimensions than of horizontal. Only two of the accidents we found involved significant deviations off the course centerline, and even then, lateral clearance wasnt a factor. It seems generally true that most approach wrecks occur on the centerline or within the horizontally protected obstacle zone. Its just that the pilots descended too soon, or failed to climb during the missed approach phase or during departure.

We found a total of four botched missed approaches, one involving a Cessna 421 that, tragically, resulted in five deaths. Botched misses involved the aircraft cruising right over the top of the airport in hopelessly low weather and crashing beyond it, off the departure end of the runway being approached. Again, this isnt necessarily the realm of the weekend warrior GA pilot.

A for-hire pilot flying boxes into Aspen, Colo., for a freight company in low vis and snow missed the airports rather demanding approach. He told investigators that because he was worried about turbulence, he flew 3.5 miles past the missed approach point before commencing the procedure, something you simply cannot afford to do anywhere, but especially in high terrain as threatening as that around Aspen. The Caravan collided with trees-both occupants were lucky to survive.

We expected to see more examples of pilots turning in the wrong direction or failing to climb while executing a missed approach, but these kinds of accidents seem rare. Only one accident involved an aircraft which failed to climb sufficiently during an IFR departure.

Cat and Dogs

The rest of the improper IFR accidents we reviewed followed no particular pattern from which we can draw any useful conclusions. They were a mix of pilots encountering weather they couldnt handle, mis-set nav frequencies, inability to intercept and track course and spatial disorientation. In our view, the latter doesnt really meet the test of improper IFR because the basic scan and the ability to keep the airplane upright isnt a procedure, its a skill. If you lack it, you cant even play the procedural game and expect to survive.

Two other types of accidents are worth mentioning: busted ILS mins and unstable approaches. Flight instructors often sell the ILS as the safest possible instrument approach, and the accident data would seem to support this: We found only three accidents in which pilots came to grief over what appears to be intentionally or accidentally busting ILS minimums. Descending below decision altitude/height on an ILS while searching for a runway in low weather probably happens more often than most of us are willing to admit. But if the glideslope needle remains centered and the pilot is just trying to squeak out another 50 feet, hes probably not going to merit an NTSB file. But you certainly cant count on that.

Weve seen enough accidents involving multiple approaches to flag them as potential trouble. But on second review, the risk may be somewhat overrated for a disciplined, competent IFR pilot who can fly centered needles all day and miss when he needs to miss or try again somewhere else. Nonetheless, get-home-itis can be a powerful lure to the dark side.

In one accident, a Cessna 210 pilot trying to get into Peoria, Ill., in zero-zero weather (at night) came to grief on his second ILS attempt. Controllers told the pilot that nearby Quincy and St. Louis had landing minimums, but he replied, “I dont want to spend the night in Quincy.”

The airlines have a superb safety record for many reasons, one of which may be their insistence on flying stable approaches. Thats not to say that general aviation pilots cant fly an unstable approach safely, say, one in which airspeed is carefully reduced as the approach progresses. But there are limits.

In one accident in Chino, Calif., the pilot of a Swearingen SA-226 caught a bad vector for the ILS that put him 650 feet above the glideslope at the outer marker. Instead of reverting to the missed approach to try again, he pitched the nose over in search of the glideslope, flew right through it and crashed 1000 feet short of the runway in thick, 1/16th-mile fog. Incredibly, he survived.

Wrapping It Up

Whats most encouraging about this review of improper IFR accidents-hardly our first, by the way-is they appear to be in decline. Theres no way to know if this is due to decreased flight activity, better trained and more experienced pilots, or the impact of GPS with vertical guidance. Or, perhaps, a combination of these factors.

Still, we think our analysis reveals what it always has: The highest risk level is descending below MDA on a non-precision approach. Whether pilots do this inadvertently or by design is immaterial to the outcome. A pine tree coming through the windshield is remorselessly uncaring about the pilots intentions, good or bad.

Although many of these accidents occurred at night, were not sure we can directly attach darkness as a factor. None of them occurred because the pilots couldnt see the runway or airport environs-they happened because pilots departed from the published procedure. Thats what defines improper IFR, and the way to avoid it is to do exactly what the approach plate says.


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