Part 2 – The NTSB Missed a Critical Safety Recommendation in a Runway Excursion Accident Report: Is the Runway Contaminated?
- Dan Boedigheimer
Would you apply wet runway landing performance numbers in that instance? That is one of the key challenges in determining accurate landing distance data. At 200 knots 10 miles from the airport, how can you accurately assess runway condition at an uncontrolled airport? Sure you could always be conservative and assume the worst, but how often would you end up unnecessarily diverting?
The Aircraft Flight Manual (AFM) supplement for wet and contaminated runways states “contaminated runway performance assumes that any dry snow, wet snow, slush or standing water…possesses a specific gravity as shown” in the table. Even at a controlled airport where a trained observer is conducting a runway condition assessment, pilots are not given the specific gravity of any contamination. There is a note in the AFM supplement that “if specific gravity is not reported, then the value which gives the longest field length should be assumed.” Since the longest field length value would exceed 10,000 feet you would need to assume anytime there is precipitation in the forecast you should limit operations to only a handful of airports. Does the AFM for the aircraft you fly have a similar reference to specific gravity of contamination?
Knowing that there were some rain showers that had moved over the airport, the decision for me would have been a determination if I considered the runway wet or effectively dry. The AFM defines a wet runway as “sufficient moisture on the runway surface to cause it to appear reflective.” Although that definition is difficult to apply for your destination during the day, it would be nearly impossible to determine at night when landing. The definition for a dry runway includes runways which have been specially prepared with grooves or porous pavement and maintained to retain ‘effectively dry’ braking action even when moisture is present.”
Runway 28 at MAC was not grooved, which is an important lesson to take away from this accident. As part of your preflight planning, do you know where to look to determine if a runway is grooved? As you can see in the airport diagram in government TPP charts, it does not indicate if the runway is grooved or not. Jeppesen charts will note “grooved” in the additional runway information section and the airport facility directory will note “GRVD” next to the type of runway surface (NOTE: the airport remark “Possible standing water on Rwy 10-28 during and after heavy rain” in the airport facility directory was not published at the time of the accident). Based on the definitions provided in the AFM, if there is any moisture present on a runway that is not grooved, you should consider it to at least be wet.
For performance calculations in the Beechjet, standing water is defined as “a runway is considered to be contaminated when more than 25% of the runway surface area…is covered by surface water more than 3 mm (0.125 inch) deep.” This is as nebulous to a pilot as the specific gravity of the contamination. Wet runway condition reports are not given in mm of depth. This assessment is much easier done while on the ground for takeoff than as a landing assessment. The difference between the runway being wet or having standing water is the basis of a lawsuit between the aircraft operator and the city who owns the airport. I am not going to focus on that difference other than to point out that as a pilot, this only compounds the issue of an accurate runway assessment. Until airport real time runway assessments are reported in the same values provided in aircraft performance charts, their value remains limited. Previously my assumption was if the runway is reflective, it should be considered wet. Only in extreme precipitation would I have made an assessment there may be standing water, and in that case there are other reasons I should not be landing at that airport. A lesson I learned from this accident is not all runways should be considered to be effective at shedding water after a storm has passed over. The only determination of the effectiveness of a runway at displacing water a pilot has is if the runway is grooved or not. With this feeble standard, I will be more conservative when operating to runways that are potentially wet. This will include planning for and carrying the fuel for a suitable alternate, even if the forecast ceiling and visibility don’t require it.
Now to the moment that things went wrong for the crew of N428JD. The aircraft touched down approximately 1000 feet from the end of the runway. A witness reported seeing the aircraft “engulfed in a large ball of water vapor” while the crew hydroplaned down Runway 28 that had a friction coefficient of wet ice. Four seconds after touching down, the PM called “hydroplaning.”
Up next in this blog series is a focus on landing performance data as well as more lessons learned from this accident.