Slick Runways

American Eagle Embraer-145 at rest off Runway 10L at ORD after crosswinds blew it from the icy runway (courtesy WLS-TV).

Author: Karsten Shein, Ph.D  

A passenger video making its rounds on the Internet shows the moment an Embraer 145 lands and is pushed off runway 10L at O’Hare International Airport (ORD) on November 11, 2019.

Fortunately, though the gear collapsed, no one was injured. Unfortunately, such events occur several times every winter. ATIS at the time of landing indicated winds from 350 at 19 kts gusting to 28 kts (35 kph gusting to 53 kph), a ceiling of 150 m (500 ft) and an RVR of under 1500 m (5000 ft) in blowing snow. Not only does this suggest a crosswind component of around 22 kt (the aircraft has a limit of 30 kt), the video clearly shows that the runways and taxiways were covered in snow.

Any time a runway is anything but dry, pilots should expect reduced handling. Although runways may be grooved for increased traction and water channeling, aircraft tires are generally not designed for traction on wet or snow-covered surfaces. As a result, it may be difficult, if not impossible, to stop on a snow-covered runway, and crosswinds well below an aircraft’s limit can push an aircraft laterally from the pavement (crosswind limits are based on the maximum crosswind the test pilot was able to land in on a dry runway).

Larger airports may be continually clearing the runways, but in doing so, the plows and sweepers often compact snow into the runway grooves, rendering their benefit useless. In several accidents, emergency responders noted that they had great difficulty reaching the aircraft due to the slickness of the runway. Even when snow has been cleared, blowing winds can re-cover a runway in seconds, and often the initial warmth of the concrete causes early snow to melt and refreeze beneath later snowfall, hiding icy patches. Importantly, airports usually do not apply chemicals or salt mixes to runways or taxiways because of their corrosive properties. This means that ice on those surfaces may not be fully eliminated until the surface temperature rises above freezing.

Departing pilots should monitor the weather with regularity, even as they are taxiing. Not all taxiways will be lined up with the wind, and a strong crosswind on a narrow, icy taxiway can spell disaster. Also, any report of freezing rain means surface icing should be assumed. Ground controllers may provide a report on taxiway and runway condition, received from other pilots and ground crew.

Similarly, landing pilots need to be aware of the condition of the runway and any crosswind. It is a good idea when runway conditions are less than optimal to cut your aircraft’s crosswind limit in half to compensate for slick conditions. Also, just because an aircraft landed safely before you, doesn’t mean that you will as well. They may have landed during a lull in gusts, while you get hit by a strong gust just after you plant your mains on some snow-covered ice.

Pilots should be especially wary of blowing snow. Not only can it reduce or eliminate visibility at a critical time, it also tends to form a thin and very slippery film that has not had a chance to compact and fuse with the surface. As a result, you may experience something akin to hydroplaning, where your tires are not actually in contact with anything but loose snow. This makes it very easy for any lateral forces to throw you off your track. No amount of cross-control or differential engine braking will help to stop your drift. Often, because adverse winter conditions may last a while, a prudent choice is to try a landing at an alternate airport where conditions are more favorable.

Once you land on a contaminated runway, you should slow as much as possible without hard tire braking (use spoilers and even reverse thrust within acceptable engine pressure limits). Braking often leads to a skid. Turning can also break the tires free on slick pavement. You should be moving very slowly (~ 5 mph (8 kph)) before turning onto a taxiway. If a skid is encountered and your aircraft is equipped with antilock brakes, maintain firm pressure, otherwise release the brakes and attempt to steer into the skid. If the tires can roll, there is a chance to regain some control.

METAR REPORTS FOR ORD AT THE TIME OF THE RUNWAY EXCURSION ACCIDENT:

  • KORD 111345Z AUTO ///19KT 1SM -SN VV011 M05/M06 A3020 RMK P0000 T10501060
  • KORD 111350Z AUTO ///17KT 1SM -SN VV011 M05/M06 A3021 RMK P0000 T10501060
  • KORD 111351Z 35017G26KT 3/4SM R10L/4000V5000FT -SN BLSN VV011 M05/M06 A3022 RMK AO2 PK WND 35028/1331 SLP240 P0001 T10501061 $

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