December 1, 2006
By Dan Namowitz
This article launches a 13-part series highlighting the types of accidents that occur in a particular season of the year. Each month we'll look at a primary accident cause, examine the reasons for the accidents, and provide tips and advice on how to avoid those accidents. This month it's contaminated runways. Next month it's icing scenarios. We welcome your feedback and experiences.
Every day's a weather day after the first snowfalls of winter arrive in colder regions. Now a whole set of conditions, accompanied by a cryptic stream of abbreviations to describe them, shows up in notams, regular and special surface weather reports, automatic terminal information service broadcasts, and verbally from the tower. After the season's first light dustings of snow give way to accumulating storms and snow-removal operations, pilots need to inform themselves continually about runway, taxiway, and ramp conditions.
Meanwhile, the unwary and the unlucky will fall victim to traps that contaminated surfaces hold in store for aircraft. If you are a pilot who can't or won't let winter conditions keep you down, ramp up your efforts to proceed safely. Some object lessons in the pitfalls that have ensnared others are worth studying too.
A snowy runway isn't just a slippery place for a takeoff or a landing, stealing traction when you need it most, as in crosswinds. It's a place where aircraft performance is mysterious: The runway may not have been plowed full length and width, making its surface inconsistent and unpredictable, or if it's a grooved runway, it will drain better than one that isn't. Bottom line: Know what you've got.
A snowy runway can be hard to spot from the air — a not-so-nice distraction on a tricky approach. Many airports don't plow all runways or taxiways. Get in trouble on a runway notamed closed, or mired on a taxiway not maintained for winter use, and life gets complicated. Check the airport/facility directory's airport remarks for your destination. Then check notams for late developments.
No casual preflight research allowed here. Much information you'll need will be tucked away in obscure places. What are the weather conditions at the surface at your destination right now? To find out, you need to get the METAR (aviation routine meteorological report) or any SPECI (special report) for the airport. There's nothing poetic about a METAR; it's a string of symbols, codes, and shorthand that takes practice to comprehend.
What you most want to see about runways comes at the end of the METAR code stream, in the remarks (after the altimeter setting and separated from it by a slash). An example: SB15E40 — this looks like a license plate number or someone's login password. Don't mistake it for a line of code only of interest to geeks. It says that snow began at 15 minutes after the hour and ended at 40 minutes past. Remarks include: SNOINCR 1/8. Snow increased an inch in the past hour, and there are 8 inches on the ground. Show me where you'd look in your pilot's operating handbook to know how your aircraft performs when taking off on 8 inches of snow.
Along with snowstorms come snow-removal operations (see "Keeping a Big Airport Snow-Free," right). When you arrive, these may not be complete. During a briefing, or when checking notams en route or from an automatic terminal information service broadcast, you may learn that one or more runways are closed for snow removal. Or that some time is required before you can land. That's known as a PPR time, say, 20 minutes prior permission required.
Even if the runway is available there may still be, in notam language, PSR (packed snow on the runway), SLR (slush on the runway), or LSR (loose snow on the runway). If you land off the centerline to avoid ice, or when taxiing, watch out for SNBNK (snowbanks caused by plowing). There could be snow-removal equipment in proximity. Some of these vehicles are huge; most have flashing lights. Occasionally someone doesn't get the word that it's time to let the aircraft land again, so be ready to make that out-of-the-flare go-around.
If braking advisories are in effect, monitor whether runways have BRAG, BRAF, BRAP, or BRAN — notam contractions telling you that braking action is good, fair, poor, or nil. A pilot once read me some weather and construed the N in BRAN for normal instead of nil. Review those contractions! Note whether the report was given by a pilot of an aircraft that recently landed — and of what type — or by a ground vehicle.
That's the planning side. But winter weather moves fast. Information also arrives during airborne updates; you'll use it to cope with changing conditions. As with any notam or pirep, when the report originated is as important as what it says. Then consider how the weather has been behaving since the report was filed. Better? Worse? Traps still loom. Long ago a student pilot landing a Cessna 172 on a sunny day encountered a runway contaminated by refrozen, melted snow from a recent storm. He sat perched atop glare ice, unable to turn onto a taxiway. The aircraft was shut down and turned by hand. Taxiing was treacherous and slow.
Get that thing off the runway
If the idea of a ground vehicle infringing on an aircraft approaching to land on a snowy runway seems melodramatic, consider what happened in Huntingburg, Indiana, on December 18, 2000. An iced-up Beechcraft 58 Baron landed just short of the runway, under night instrument conditions, having missed one approach after conflict with a ground vehicle. It was a web of events that the NTSB said was caused by the "snow-covered runway, the ice-contaminated windshield, and the airport snow removal performed by the driver of the vehicle."
The flight from Fort Myers, Florida, had coped with icing en route. The right side of the windshield was iced by the time Evansville Approach told the pilot to expect the VOR Runway 9 approach in Huntingburg.
From the pilot's written report: "Talked with Huntingburg [and] told them we were about 15 [minutes] out. Flew VOR 9 [approach] to Huntingburg. Broke out over Holland [Indiana]. Had the airport [at] 5 miles clear [and] cold [at] 1,500 feet. Started picking up a little precip. No problem. Upon arrival (at the) airport I was about 1 1/2 [miles out and] started to call in. Saw movement on taxiway. At 1/2 mile out tractor with snowplow pulled out on [runway] — I started a missed [approach]. Talked with Evansville [approach] told them I could do a go around (circle to land). At about 1,200 to 1,300 feet pick up more ice on windshield. I still had good vision. But [finding] the alcohol bottles would not work, I set up on final. Had the runway made and decreased power and touched down 15 feet short of centerline. Wheels landed on wet ground [and] caught the edge of runway. Mains broke off. Flew down the runway, landed. Skid down [runway] and off the side."
Here's the other side of the story: "The driver of the snowplow stated that he made a 'swipe' on the runway when he heard a '15-minute call' from an aircraft. At this point, he was at the end of the runway when he pulled onto the taxiway. The driver stated that he did not hear any additional radio transmissions while holding short of the runway. He contacted the terminal to confirm that there were no additional radio transmissions prior to his taxiing onto the runway. Personnel within the terminal reported that they had not heard any additional radio transmissions. He stated that prior to taxiing onto the runway, he did not see any traffic when he 'glanced,' but did not 'look,' for traffic on approach for Runway 9. He did not make any radio transmissions when he taxied onto the runway. While on the runway, he heard an aircraft fly overhead and a radio transmission saying, 'Get that thing off the runway.' According to the airport manager, all the vehicles are equipped with two-way radios and lights. The strobe lights on the snowplow were on during plowing."
The pilot had additional reflections. "There are several things I could have done. One, I could have stayed in Florida. Two, I could have gone to Evansville with a tower and ILS. Three, when the tractor pulled out I should have done a full missed approach, and not let myself get rushed, with the windshield and vision. Four, I should have carried more power instead of trying to land for a long roll out. I was trying to use as much runway for the roll out as...the braking action was only fair. Five, this was my decision and it was not the best decision."
The NTSB report reminded readers of recommended procedures for using common traffic advisory frequencies: "At 1540 [3:40 p.m.] a notice to airmen (notam) was issued for 1/4 inch snow and poor braking action. At 1831 [6:31 p.m.] a second notam was issued for closure of the airport." The accident occurred at 6:15 p.m.
'The driver then exited the vehicle before the impact' Although the report above describes a whirlwind of motion, it is also true that things can go wrong even when everyone is almost at a standstill. On December 20, 2004, an early morning American Airlines flight from Theodore Francis Green State Airport, Providence, Rhode Island, was pushed back. There were 82 passengers and five crewmembers aboard the McDonnell Douglas MD-82.
Two narratives appear in the NTSB report, and they are excerpted here: "The flight crew reported that the airplane was being pushed by a tug, on an icy ramp. During the push-back, the tug slid left on a patch of ice, and struck the airplane's right side, damaging the nose landing gear, three longerons, and two frames."
And, "The driver of the tug stated that during push-back, he initiated a slight turn and the airplane began to move toward the tug. The driver then exited the vehicle before the impact." Weather reported at Providence about 30 minutes prior to the mishap was "wind from 330 degrees at 14 knots; visibility 9 miles in light snow; broken ceiling at 1,700 feet; overcast ceiling at 2,100 feet; temperature 25 degrees F; dew point 22 degrees F; altimeter 29.56 inches Hg."
One problem when contending with a contaminated surface is that it is simply hard to see. Nine days later, an iced-up Piper PA-32 and a snow-covered runway conspired to foil a landing at Fulton County Airport, Johnstown, New York.
From the NTSB report: "According to the pilot, while performing the GPS approach to Runway 28, ice accumulated on the airplane. He broke out of the clouds at an altitude of 1,600 feet; however, he had difficulty visually identifying the runway, due to the snow cover on the ground. The pilot stated he was at an airspeed of 100 knots (about 65 percent power) while on short final, and as he reached the runway threshold, he 'cut the power,' and applied the third notch of flaps. The airplane then 'stalled,' and landed hard on the runway." There were no injuries to the pilot or passengers.
This was not Stewart airport
Here's what a crewmember on a Boeing 727 had to say in a filing with the NASA Aviation Safety Reporting System (ASRS) about nearly landing at a misidentified airport in New York. "Visibility was day underneath but milky in early morning daylight. Ground was entirely snow covered. Vector was 090 degrees for Runway 9. At about 2,800 feet we saw a runway straight ahead for which we were lined up. We called the runway and were cleared to do a visual approach and cleared to land. We were fully configured to land. The captain realized once we got closer that this was not Stewart [International] Airport. We did a go-around, contacted approach and got vectors to Stewart. We also firmly requested them to turn the ILS on. Landing was uneventful."
When a Cessna 560 Ultra Citation V went off the end of a runway after landing at Westchester County Airport, New York, nil braking compounded other problems, recounted in an ASRS report. "The approach and landing were normal and at touchdown max braking was applied and continued throughout the rollout. The aircraft exited the end of the runway into a grassy/muddy area approximately 100 to 150 feet from the departure end of the runway." The reporter added, "Possible contributing factors were: rapidly changing conditions, anti-skid cycling could not be felt throughout the rollout, speed brakes may not have been deployed, duty day was at eleven and a half hours."
Update those charts
The combination of expired charts and blowing snow doesn't spell trouble — until a frequency for turning on the runway lights changes. The NTSB stated this as a probable cause when a Hawker Siddeley HS-125-700 found itself misplaced in the snow 195 feet from the centerline of the 150-foot-wide runway while landing at Jackson, Wyoming, on December 20, 2000: "The pilot's failure to follow IFR approach procedures and perform a missed approach when the runway was not in sight below approach minimums. Contributing factors were the copilot's failure to follow current ILS approach procedures and use the correct frequency to turn on the runway lights, the snowy whiteout conditions near the ground, and the dark night light conditions."
This happened to an airliner but it could happen to you: A Boeing 737-300 landed successfully on 2 to 4 inches of dry snow at Bradley International Airport in Windsor Locks, Connecticut, but after exiting the runway, "turning became impossible," reported a crew-member to the ASRS. "It took three attempts to break loose (the) steering. I suspected frozen or iced-up nosewheel steering."
Just type "snow" as a search parameter into the ASRS database query tool — your screen will fill up with reports. Not always as a primary culprit in mishaps, often just the tip of the iceberg. See what causes accidents at an airport by checking accident reports in the AOPA Air Safety Foundation Accident Database or by using a new feature of AOPA's Airport Directory online, which provides a link to accident reports associated with individual airports. Yes, it's a winter wonderland. Minding the hazards will keep your N number out of the databases that track keyword combinations such as "snow" and "aircraft."
Dan Namowitz is a writer and pilot living in Bangor, Maine.
Keeping a big airport snow-free
Bangor, Maine, is snow country. Bangor International Airport is a former Strategic Air Command air base with a runway that is 11,440 feet long and 200 feet wide.
When the weather is bad in Boston, airlines tap Bangor as an alternate. Keeping an airport like this open when winter weather sets in might not be a challenge relished by everyone. Marty Kelly, Bangor's assistant supervisor of airfield maintenance, says the trick is having a good team and good communications.
When it's time to plow that huge runway, the first thing you do is contact the airport's air traffic control staff and "find out how much of a window you have," he says. Seven trucks, each bearing a 22-foot plow blade, attack the snow, employing a technique that "wind-rows" the snow from the centerline toward the edges. Two blowers follow the trucks. It takes seven or eight minutes to do a pass in one direction. Doing one pass north and one south is best. Twenty minutes is the most time that's usually required during delays.
Different precip gets different treatment. If the Doppler radar shows freezing rain approaching, the crew lays down a coat of potassium acetate to break the bond. Slush takes longer to remove than snow; it must be scraped off. A big challenge is keeping lights and signs visible, especially approach lights and signs at intersections of the parallel taxiway and those leading to the single runway.
The plowing crews can talk to their supervisor on a city radio and can monitor his communications with ATC. The drivers cannot communicate on ATC channels.
Braking-action reports are done in three zones (touchdown, midfield, and rollout) by an SUV-size vehicle equipped with a Tapley meter, an FAA-approved instrument, also called a "decelerometer," which measures friction. "He goes to 20 mph, shifts to neutral, and slams on the brakes." The readings are averaged. Some airlines want the numbers; some just want to know whether braking is good, fair, poor, or nil.
A high-pressure job? Lately it's been pretty sweet. Last winter Bangor was almost snowfree. And the runway at this former SAC base used to be much larger at 300 feet wide. — DN
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