Pilots Should Study Runway Condition Reports, Part 2

What is the FAA criteria for the siting of a wind sensor? According to Order JO 6560.20C, “Siting Criteria for Automated Weather Observing Systems,” the preferred siting of the wind sensor at an airport with only a visual or non-precision runway is adjacent to the primary runway 1,000 feet to 3,000 feet down runway from the threshold.  

The author added the italics for emphasis. Clearly, these indicators are not able to accurately sense the shifting wind currents in the threshold of a runway such as Telluride’s Runway 9.  

This type of rapidly-changing adverse wind close to the approach end of the runway was a contributing factor in the crash of a Socata TBM 700 on Feb. 15, 2003, at Aspen-Pitkin County Airport, Colorado. The approach was stabilized at 100 kts with landing gear and flaps in the landing position. The approach was normal until approximately 100 ft. above the runway at which time the airplane encountered a turbulence condition, causing rapid-roll tendencies right and left. 

As the pilot began his landing flare at about 15 ft. above the runway, the left wing dropped rapidly combined with a sudden high sink rate and struck the runway. Fortunately, none of the four occupants of the aircraft was injured. Winds at the time were reported 310 deg. at 6 kts. Records suggest that the winds were variable throughout the day. The NTSB determined the pilots had failed to maintain aircraft control. Contributing factors include the tailwind and the turbulence.
    
What Really Is The Temperature At The Runway?
The heat on the ramp was unbearable while walking out to the aircraft on a hot August afternoon in Lincoln, Nebraska. ATIS was reporting 108 deg. F, but it felt much worse than that on the ramp. 

Mechanics from Duncan Aviation walked out to the aircraft with their recently acquired infrared temperature detector. Their “temperature shot” from the cement showed a temperature of 127 deg. The blacktop was even worse. It showed 143 deg. 

As per company operating procedures, our takeoff performance was calculated using the reported ATIS temperature. Fortunately, we had no passengers and only a modest amount of fuel for the post maintenance test flight. Normally the takeoff distance would be relatively short at that light weight and low altitude but the end of the runway seemed unusually close when we rotated for takeoff. 

Months later I was flying with a colleague whose primary passion in life is competitive racing of high-performance automobiles. He informed me that the auto racing industry is cognizant of the difference between the race track’s temperature versus the reported air temperature. In fact, teams will purposely tune-up their engine performance in conditions as close as possible to the track conditions replicating the time of their race.
 
Certainly, this same principle applies to aircraft. When the temperature of the air at the height of our engines and wings is significantly hot, we should expect longer takeoff runs, anemic climb rates, higher speeds for takeoff, reduced engine longevity, and reduced climb gradients. Excessive temperatures will undoubtedly bake the tires and brakes during ground operations, increasing the risk of high speed tire failure and overheating wheel and brake assemblies

According to JO 6560.20C, the temperature sensor must be mounted so that the aspirator intake is 5 plus or minus 1 ft. above ground level or 2 ft. above the average maximum snow depth, whichever is higher. It can be placed at any convenient location on the airport that is protected from radiation from the sun, sky, earth, and any other surrounding objects, but at the same time, be properly aspirated.

The sensors must be installed in such a manner as to ensure that measurements are representative of the free air circulating in the locality and not influenced by artificial conditions such as large buildings, cooling towers, and expanses of concrete and tarmac to minimize the effect that the underlying ground itself might have on temperature.

I put those final words in italics for emphasis hoping that you might reach the same question I have. For the record, heat transfer is not within my engineering specialty. Many of you with soaring backgrounds will recognize the drawings in training manuals of the warmer air over heat-soaked ground to include large expanses of concrete or asphalt becoming more buoyant than air over adjacent grass-covered landscape and eventually rising as a thermal. This further reinforces my curiosity in the micro-scale temperature differences around an airport.
  
When will this adverse heat problem over the runway be most problematic? The amount of solar radiation absorbed by the ramp depends on various factors, such as the angle of the sun with respect to the ramp (the noontime sun directly overhead bombards the ramp with the highest ratio of sunshine), clear-vs-cloudy days, etc.  Dark surfaces such as asphalt absorb more radiation than lighter colored surfaces, which tend to reflect some of the radiant energy. 

It takes a lot of incoming radiation to “heat up” concrete, but once it does reach a warm temperature, it tends to retain that heat for quite some time.

Astute flight crews should scrutinize the possible sources of uncertainty when planning a takeoff or landing, we advise in Part 3 of this article.  

Pilots Should Study Runway Condition Reports, Part 1: https://aviationweek.com/business-aviation/safety-ops-regulation/pilots…