FAA begins rulemaking process to extend runway safety margins

 - September 28, 2006, 9:54 AM

The FAA has decided to create a new rule to mandate a 15-percent runway landing safety margin for commercial operators instead of trying to impose the requirement via a policy letter and changes to operations specifications. The rule will likely affect Part 91 (Subpart K fractional operations), 135 and 121 operators.

To help promote safer operations while the rulemaking takes place, the agency published a Safety Alert for Operators (SAFO 06012) that, while targeted to commercial operators, could enhance safety for any jet operator.

The SAFO, titled Landing Performance Assessments at Time of Arrival, is available at www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo.

The safety margin requirement first came to light in an FAA policy letter published on June 7 and was the result of the Dec. 8, 2005, fatal overrun accident of a Southwest Airlines Boeing 737 at Chicago Midway Airport. In the policy letter, the FAA explained that an audit of applicable regulations, advisory circulars, policies, orders, notices, ICAO and non-U.S. government requirements and other material conducted after the accident uncovered issues regarding landing performance assessment, especially on contaminated runways. The FAA found that:

• About 50 percent of operators surveyed don’t have formal policies for assessing whether enough runway is available to land, even if conditions deteriorate at the destination.

• Operators that do assess landing distance during the flight don’t all take into account runway contamination, and many do not apply a safety margin to the expected actual landing distance.

• Some third-party contaminated runway performance data indicates shorter landing distances than airplane manufacturer data, and some operators’ data isn’t updated as manufacturer data changes.

• Flight-test-derived landing performance data published in flight manuals is “not representative of everyday operational practices.” While some manufacturers provide factored landing distance data that is more operationally realistic, landing distances determined for certif- ication are shorter than normal operational landing distances.

• There is confusion about credit for the use of thrust reversers in landing performance.

• While pre-takeoff calculations of landing distance add a safety margin and commercial operators perform these calculations and take into account forecast runway condition, there is no regulatory requirement to add a safety margin to landing distance assessment at time of arrival.

SAFO 06012 recommends that jet operators add a procedure during flight and before arrival to “assess landing performance based on conditions actually existing at time of arrival, as distinct from conditions presumed at time of dispatch. Those conditions include weather, runway conditions, the airplane’s weight and braking systems to be used. Once the actual landing distance is determined, an additional safety margin of at least 15 percent should be added to that distance.”

If the landing distance available is less than the actual landing distance plus 15 percent, “flight crews should not attempt to land” unless it’s an emergency. The SAFO notes that the landing distance available may be shorter than the actual runway length.

In a 2005 study of overrun accidents by National Aerospace Laboratory (NLR), Amsterdam, The Netherlands, researcher G.W.H. van Es sought to “estimate the risk associated with the various landing factors (excess speed, tailwind, runway condition and so on),” according to the study. The NLR study looked at more than 400 airline overrun accidents between 1970 and 2004.

The NLR study (see facing page) breaks out the number of accidents and their associated risk factors. Some accidents involved multiple risk factors, which is why the total number of accidents listed is more than the total number of accidents studied and why the percentages add up to more than 100. “The highest risk increase occurred when the aircraft touched down far beyond the threshold (long landing), followed by excess approach speed,” the study stated. Non-precision approaches, while a normal procedure, add a high amount of risk to landing attempts.

The study also calculates risk ratios for six risk factors–non-precision approach, long landing, excess approach speed, visual approach, significant tailwind, high on approach. The larger the risk ratio value the stronger the association between the factor and the landing overrun accident risk. All of these risk factors increase the chances of an overrun accident, but some add more risk than others. The study recognizes that some of these factors are interrelated.

This report and the information that is available regarding the Southwest Airlines accident raise the question of whether the FAA’s landing margin recommendations and rulemaking will have any effect on the root causes of runway overruns.
Rich Boll, a pilot for a large Midwest corporate aircraft operator, believes that addressing the root causes of overruns is exactly what the SAFO does. “It was never the intent of the SAFO that the pilot/operator simply adds 15 percent to the FAR 25 actual landing distance as found in the AFM,” he explained.

“Rather, the intent was and is with the SAFO that the operator/ pilot add 15 percent to the actual landing distance based on the weight at arrival, configuration, approach speed, runway conditions existing, operator/pilot operational landing technique and expected use of deceleration devices like thrust reversers.” Making this calculation should force pilots to consider the associated risk factors.

The NLR study commented on two specific areas related to the Southwest accident, use of stopping devices and runway contamination. First, the report noted that in 15 percent of the accidents studied “there was late or no application of the available stopping devices. In many of these accidents an overrun was avoidable if the available stopping devices would have been properly used. Also late or no application of thrust reversers was often found in the accidents (67 percent of all cases with late or no application of the available stopping device).”

With regard to runway contamination, the NLR study added, “Unfortunately, despite the great effort made so far, an acceptable solution to this problem of measuring runway friction and correlating it to aircraft landing performance is still to be found.”

The FAA is concerned about runway contamination issues and held a workshop on the subject on August 7 and 8, inviting commercial operators and airport personnel to discuss the issue and share information. Presentations and contact information from the workshop are available at www.faa.gov/news/conferences_events/
runway_cond/. The four work groups, which welcome additional industry participation, are addressing contaminated runway terminology, condition, technology and dissemination of information.

Rulemaking takes a long time, and runway overruns remain a problem. Boll, who has studied runway performance issues in depth, offered his opinion about the FAA’s action: “I hope operators will take the SAFO to heart. Just because [the FAA policy change] was dropped doesn’t change the problem at hand. The aircraft doesn’t care about legalities. The aircraft obeys two laws, the laws of physics and the laws of aerodynamics. It knows how much distance it needs to land and stop and if that length of runway is not available, an overrun will occur.”