ATR 72 Crew’s Ingenuity Cited In Rare Sea Salt Incident
May 2, 2015 John Croft | Aviation Daily
"The crew of an Aer Arann ATR 72 flying for Aer Lingus is credited with “good airmanship” in finding a way to remove salt deposits that had completely blocked the view forward from the twin turboprop’s windscreen while attempting to land at the Cork Airport in January 2014.
While such incidents are rare, the wind and weather conditions that night also caused similar, but less severe, sea salt coatings to form on a second ATR 72 and an Airbus A321 approaching the airport, both of which were able to land, according to a final report by Ireland’s Air Accident Investigation Unit (AAIU).
Pilots on the incident flight, which had four crew members and 42 passengers aboard, aborted a first landing attempt due to a large change in winds, which were measured at 28 kt. and gusting to 41 kt. The windscreen was clear on the first approach.
Following the missed approach, air traffic control vectored the aircraft over land and sea back to the airport at 3,000 ft. altitude, during which time the captain noticed “a considerable build-up of white contamination forming on the windscreen” but did not immediately know its origin. During the second approach, the captain said the residue made the windscreen opaque, “diffusing the [runway] lights into a complete blur,” and forcing a second go-around.
The windscreen wipers had no effect in clearing the residue as the atmosphere was dry, the captain stated, adding that the windscreen heaters, turned on to prevent any ice build-up, may have exacerbated the problem by drying the salt residue. The ATR 72 does not have windscreen washer. Investigators asked the French civil aviation safety bureau, BEA, as well as ATR and Airbus if there had been any similar incidents in their records. All said no.
However research compiled by the U.S. National Oceanic and Atmospheric Administration (NOAA) shed light on the issue. A NOAA Lockheed WP-3D four-engine turboprop research aircraft in 2007 had been flying at approximately 3,000 ft. altitude about 500 nm. east of Newfoundland in wind speeds of 85-95 kt. when it lost power to three engines due to sea salt accretion. The crew was able to restart the engines and return to Newfoundland, but noted “very limited visibility through the windscreen” on landing due to the salt accretion. The final report on that incident linked high wind speeds and a lack of precipitation in part to “the presence of high concentrations of sea salt aerosols.” A follow-on report by the U.S. Naval Research Lab determined that under worst case conditions, the salt residue could ascend as high as 5,000 ft.
After the second landing attempt, the ATR 72 crew contacted the airline engineering center by mobile phone, learning about the visibility problems the other ATR 72 experienced earlier that evening due to sea salt. The captain decided to fly toward a nearby area of rain displayed on the weather radar in an attempt to clear the salt. Upon flying through the shower, “a small area at the base” of the captain’s windscreen “cleared of contamination,” the AAIU says. During the third approach, controllers turned the runway lights to full brightness as the aircraft declared an emergency due to the limited windscreen visibility.
An area of rain on the final approach further cleared the windscreen and the aircraft landed safety.
Following AAIU’s investigation, the aircraft operator, now Stobart Air, issued a Flight Crew Instruction on sea salt aerosol accretion, citing much of the information in the AAIU’s final report and advising crews “that it may be necessary to fly through precipitation prior to conducting a landing.”
Given the rarity of the event, the AAIU did not issue any specific safety recommendations."
http://www.aaiu.ie/sites/default/fil...202015-007.pdf