How Compounding Risks Drive Runway Excursions

Runway excursions rarely result from a single factor. More often, they develop when several manageable risks combine into a situation that leaves little margin for error.

FAA Advisory Circular 91-79B emphasizes the “compounding effect” of operational hazards, and runway excursion accidents in business aviation repeatedly demonstrate how tailwinds, unstable approaches and contaminated runways can align to overwhelm crews who fail to recognize the deteriorating picture early enough.

The Anatomy of a Compounding Accident

A Learjet 35 runway excursion in San Marcos, Texas, provides a textbook example. The NTSB investigation found the crew landed with a 15-knot tailwind on a wet runway after an unstable approach in gusty weather conditions. The airplane touched down halfway down the runway at 124 knots with only about 2,600 feet remaining and subsequently hydroplaned off the departure end. Together, these conditions created an accident chain.

The flight crew initially received weather information that was approximately one hour old and reported winds favoring Runway 13. However, convective activity near the airport caused the wind to shift significantly before arrival. By landing time, there was an approximate 15-knot tailwind for Runway 13.

Managing Dynamic Wind Conditions

Dynamic wind conditions are a major runway excursion hazard because they often evolve faster than crews anticipate. A preflight risk assessment should not only identify the forecast winds but also evaluate the likelihood of changing conditions at the estimated time of arrival, especially when convective weather or frontal activity could significantly alter runway conditions before landing. Thunderstorms, gust fronts and frontal boundaries should immediately raise concern for runway changes or rapidly shifting winds.

AC 91-79B stresses the importance of continuously reassessing operational conditions during the approach phase. That means crews cannot rely solely on the METAR received earlier in the flight. Staying ahead of changing conditions requires an active strategy. Crews should brief how they will monitor winds during their arrival by requesting updated tower wind checks, listening for AWOS or ATIS updates, monitoring FMS wind indications and tasking the pilot monitoring with visually checking the windsock on final approach.

The Perils of Unstable Approaches

In the San Marcos accident, changing winds were only one piece of the problem. The NTSB found the approach itself was unstable. Recorded flight data showed descent rates exceeding 2,000 feet per minute shortly before landing, beyond the operator’s stabilized approach criteria.

An unstable approach, combined with a tailwind, almost always results in a long touchdown. That is exactly what occurred here. The airplane touched down halfway down the runway, eliminating much of the stopping distance needed for a wet runway landing.

This highlights one of the most important principles in runway excursion prevention: A go-around is not a failure. It is often the safest and most professional decision a crew can make. AC 91-79B and the NTSB both emphasize that crews should not attempt to “salvage” an unstable approach. The accident first officer later stated that a go-around should have been initiated before landing.

Summer Convective Hazards and Runway Contamination

The final hazard in this accident was runway contamination. Many pilots primarily associate contaminated runway operations with winter weather, but summer convective weather creates hazards as well.

The San Marcos runway was reported wet, and the first officer stated the airplane appeared to hydroplane after touchdown. The challenge with convective weather is that runway conditions can deteriorate faster than airport reporting systems can update. Standing water from a passing rain shower may develop within minutes, while braking action reports lag behind actual conditions.

This is why crews should maintain a conservative mindset anytime rain showers are near the airport environment. Even if runway condition codes appear acceptable, pilots should recognize that heavy rain and standing water can significantly increase stopping distances and reduce braking effectiveness. Combining those conditions with a tailwind or long touchdown can quickly erase all available safety margins.

Final Thoughts

Business aviation runway excursion data continues to show the same recurring pattern: Accidents are rarely caused by a single issue. Instead, they result from multiple operational threats combining during the approach and landing phase. The safest crews are the ones who identify those threats early, continuously reassess changing conditions and are willing to execute a go-around before a manageable situation becomes an accident.