The Many Factors That Lead to Runway Overruns

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.

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."

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

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.

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)

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