It was dark when he approached Steamboat Springs. Cleared for the RNAV (GPS)-E approach for Runway 32 at Bob Adams Field (KSBS), he began his descent 20 minutes out, turned eastward at the initial approach fix, HABRO, and then northward at MABKY intersection.

The design of the approach brings you up a valley between high terrain to the east—where a number of peaks rise above 10,000 feet—and 8,250-foot Quarry, aka Emerald Mountain, to the west. The final approach fix (FAF), PEXSA, is aligned with the runway; the 5.4 nm leg from MABKY to PEXSA, however, is oriented at 353 degrees and requires a left turn of 30 degrees onto the 4.6 nm final approach course.

The field elevation at KSBS is 6,882 feet. Category A minimums are nominally 1,300 and 1¼ with a minimum descent altitude of 8,140 feet. The missed approach, begun at the runway threshold, calls for a climbing left turn back to HABRO at 11,300 feet.

The descent profile specifies crossing altitudes of 9,700 feet at the FAF and 8,740 feet at an intermediate fix, WAKOR, 2.4 nm from the FAF. From WAKOR to the threshold is 2.2 nm. Once passing WAKOR, the pilot could step down to the minimum altitude and start looking for the runway.

The Meridian tracked the ground path of the approach with electronic precision. The profile was not so perfect. The airplane crossed the FAF at 9,100 feet, 600 feet below the required altitude. At WAKOR it was 540 feet low and for all practical purposes already at the minimum allowable altitude for the approach.

At WAKOR, rather than continue straight ahead toward the runway, the Meridian began a left turn, similar to the turn required for the missed approach but 2 miles short of the prescribed missed approach point. The ground track of the turn, executed at standard rate, had the same machine-like precision as previous phases of the approach—but not the profile. Rather than immediately climb to 11,300 feet, as the missed approach required, the Meridian continued to descend, reaching 7,850 feet, less than 1,000 feet above the field elevation. It then resumed climbing but not very rapidly. One minute after beginning the left turn at 8,200 feet and on a heading of 164 degrees, it collided with Quarry Mountain. At the time of impact, the landing gear was in the process of being retracted.

When the Meridian arrived in the vicinity of Steamboat, the weather had deteriorated to 1,200 feet overcast and 1 mile visibility—below minimums for the approach. The National Transportation Safety Board limited its finding of probable cause to the statement that the pilot had failed to adhere to the published approach procedure and speculated that he had become aware of the below-minimums conditions only during the approach. Indeed, he would have become aware of the low ceiling by the time he reached WAKOR because he was already practically at the minimum descent altitude there.

He was apparently unprepared for this unexpected development.

The Meridian was equipped with a lot of fancy avionics that recorded every detail of the approach, and the accident docket includes extensive graphic depictions of those records. (These are not included in the published report.) What is striking about them is the contrast between the undeviating steadiness of headings and the large random fluctuations in airspeed, vertical speed, and altitude, which are evidently being controlled by the pilot. During the last two and a half minutes of the flight, the Meridian’s airspeed fluctuated between 89 and 110 knots and its pitch attitude between minus-5 and plus-10 degrees. Approaching WAKOR, its vertical speed was zero. Crossing WAKOR and beginning the left turn, the vertical speed first dipped to 1,500 fpm down, then, 10 seconds later, corrected to 1,300 fpm up. Ten seconds after that, it slumped again to zero before shooting back up to 1,500 fpm, holding that rate momentarily and then dropping again. The impact occurred a few seconds later.

The pilot’s logbook, which recorded 580 hours total time with 43 hours of simulated instruments and 45 hours of actual, contained four instances of this same GPS approach in the month preceding the accident. In some of those log entries, no actual instrument time was recorded, and at least two of them ended with a low approach but no landing. In some, if not all, of those approaches, the pilot was evidently practicing in VMC. Plots of two of those approaches, one a month earlier and the other a week earlier, display the same precision in ground track as the one that led to the accident, so it appears that he was relying on his autopilot for horizontal navigation.

• READ MORE: When VFR Turns into IFR

Being based at KSBS and having repeatedly flown the approach in good weather, the pilot would have been aware that the terrain below him never rose above 7,000 feet. He might therefore have believed, consciously or unconsciously, that as long as he didn’t get much below 8,000 feet, he wasn’t going to collide with anything. That idea could have factored into his starting the missed approach 2 miles short of the runway. Or perhaps he simply forgot about Quarry Mountain. Or, possibly, he made the decision to miss at WAKOR and began the turn without even reflecting that an important element of any missed approach is the location at which it starts.

His unsteady control of airspeed and pitch attitude, and his failure to retract the landing gear until a full minute after beginning the miss, suggest a pilot unaccustomed to balked approaches and now struggling with a novel situation. Anticipating VFR conditions, he had not filed an alternate and would now have to make a new plan and execute it in the air.

The difference between simulated instrument flying and the real thing—compounded, in this case, by darkness—is difficult for novice instrument pilots to imagine. It is not just a matter of the complexity of the required actions. It is the effect that anxiety, uncertainty, or surprise may have on your own capabilities. What looks like a dry script on a piece of paper can become a gripping drama—comedy or tragedy—when the human protagonist steps onto the stage.

This column first appeared in the September 2023/Issue 941 of FLYING’s print edition.

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The local television crews captured video of the aircraft off the end of the 4,884-foot by 100-foot runway, noting “It traveled all the way to the end of the runway before sliding off, possibly due to the wet tarmac.” The airplane traveled through the airport perimeter fence before coming to rest on what appeared to be a street.

Then the questions began: Did the brakes fail? Was there insufficient braking action on the wet pavement? What caused this runway overrun?

The FAA and the National Transportation Safety Board (NTSB) have been studying that question for years.

Don’t Skimp on Preflight Planning

FAR 91.103 requires the pilot to be familiar with all available information prior to the flight which includes aircraft performance—takeoffs and landings. Yet many pilots get lazy and stop doing the calculations, falling into the complacency trap “it’s only me in the aircraft,” or “I’m just going out for touch-and-go flights, and I know the runway real well.”

Don’t be this pilot. Accidents happen when pilots become complacent.

In 2018 the FAA released Advisory Circular AC 91-79A, Mitigating the Risks of a Runway Overrun Upon Landing. According to the AC, the FAA and the NTSB determined runway overruns during the landing phase of flight account for approximately 10 incidents or accidents every year, “with varying degrees of severity, with many accidents resulting in fatalities.”

As a result, the NTSB recommended the FAA adopt training scenarios drawn from real-world conditions that a pilot might encounter. This scenario-based training is designed to increase a pilot’s recognition of higher-risk landing operations, for example when the runway is wet or contaminated by ice or snow, or if the aircraft is approaching with tailwind.

The AC goes on to state, “All pilots are responsible for knowing the operational conditions they will be encountering and being able to assess the impact of environmental situations on the airplane’s landing distance.”

What Causes Runway Overruns?

The NTSB and FAA have identified the causal factors of runway overruns.

• Unstabilized approach—be it too fast and/or too high. Basically, the pilot is behind the aircraft.
• High airport elevation or high density altitude (DA), resulting in increased groundspeed.
• Effect of excess airspeed over the runway threshold. This causes a floating tendency.
• Airplane landing weight. A heavier airplane takes longer to stop.
• Landing beyond the touchdown point, causing the pilot to run out of length and options at the same time.
• Downhill runway slope, requiring stronger brake application and difficulty slowing down.
• Excessive height over the runway threshold. You land further down the runway, eating up precious distance.
• Delayed use of deceleration devices, such as reverse thrust, beta, or ground spoilers.
• Landing with a tailwind. The FAA’s Small Aircraft Branch provided the following tailwind performance information for a few small airplanes: Cessna 150 and 152, note on the landing distance chart, “for operation with tailwinds up to 10 knots, increase distances by 10 percent for each 2 knots.” In larger, faster aircraft, the effect of a tailwind that leads to increases in landing distance can grow drastically, sometimes more than 20 percent for the first 10 kts of tailwind.
• A wet or contaminated runway. This results in a lack of braking action.

Note that the unstabilized approach tops the list—but fortunately, it is the easiest factor to address. When a pilot transitions from one type of aircraft to another—including everything from a two-place to a four-place trainer or a jet—there will be a learning curve when it comes to flying approaches. We’re taught to get the aircraft stabilized, have an aiming point for touchdown, to identify where the aircraft will come to a stop, and the go-around point if that doesn’t happen. In piston aircraft go-arounds are a little easier, as the engine usually doesn’t have to spool up like it does on a jet. When this doesn’t happen the pilot runs out of runway and ideas at the same time.

FAA’s Definition of Stabilized

The FAA definition of the stabilized approach, per Advisory Circular AC-25-735, is “a stabilized approach is one in which the pilot establishes and maintains a constant angle glidepath towards a predetermined point on the landing runway.”

The pilot does this by adjusting the airplane’s energy resulting in optimum airspeed and descent.

Stabilized approaches are based on the pilot’s judgment of certain visual clues and management of the aircraft configuration to maintain the approach.

While every runway is unique, a commonly referenced optimum glidepath follows the “3:1” principle. For every 3 nautical miles (nm) flown over the ground, the aircraft should descend 1,000 feet. This flight-path profile simulates a 3-degree glideslope.

According to the AC, factors leading to an unstabilized approach include excess airspeeds normally flown in the terminal area and or ATC clearances that require an airplane to remain at an altitude that makes interception of the normal glidepath difficult—this is the old ‘slam dunk’ approach which can be problematic even for the most experienced pilots.

If you can’t achieve a stabilized approach let ATC know, and initiate a go-around.

Arrived at the approach threshold with the aircraft configured for landing and on speed. Be very careful on approaches where a gust factor requires a few extra knots, because those extra knots mean a higher ground speed and more runway used.

According to AC-25-735, “a 10 percent excess landing speed causes at least a 21 percent increase in landing distance.” This excess speed means more braking will be required, which can result in tire damage.

The AC emphasized the management of the aircraft’s energy plus potential altitude as the approach is flown for best results, noting that flights that were above the “3:1” descent ratio, and not stable, “often had high rates of descent and high approach speeds” this was found even when the aircraft was 20 nm from touchdown, noting the approach is more at risk of being unstable when closer to the optimum “3:1” descent ratio, the approach is more at risk of being unstable when closer to the runway (i.e., 500 feet to 1000 feet height above touchdown)

More Stabilized Approach Guidance

• Multiply groundspeed in knots by 5 to estimate the appropriate descent rate in feet/minute to maintain a 3-degree glidepath.

• Use visual approach systems such as VASI or PAPI to maintain glidepath, if available.

For more information, look to Chapter 8 of the FAA Pilot’s Handbook of Aeronautical Knowledge, and Advisory Circular 91-79A.

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