AINsight: Keep It Clean

 - February 24, 2023, 11:59 AM
Deicing procedures being performed by ground crew on a business jet
(Photo: AIN)

Operating an aircraft in conditions where there is either frost or freezing or frozen precipitation present creates several hazards and challenges. On the ground, pilots must have a plan to ensure that all lifting and control surfaces are free from any form of contamination before takeoff.

A contaminated wing and/or empennage on an aircraft will decrease lift, increase drag, and can lead to a disastrous outcome. Accident reports suggest that pilots do not fully use ground deicing and anti-icing procedures or understand the intent of the FAA’s “clean aircraft concept,” which prohibits takeoff with frost, ice, or snow adhering to any critical surface of an airplane.

As an example, in November 2004, a Bombardier Challenger 601 was destroyed during an attempted takeoff at Colorado’s Montrose Regional Airport. The aircraft stalled shortly after takeoff due to ice and snow on its wings. Of the six occupants, the pilot, flight attendant, and one passenger were killed. The first officer and two passengers were seriously injured. 

In its final report, the NTSB determined the probable cause as “the flight crews’ failure to ensure that the airplane's wings were free of ice or snow contamination that accumulated while the airplane was on the ground, which resulted in an attempted takeoff with upper-wing contamination that induced the subsequent stall and collision with the ground. A factor contributing to the accident was the pilot’s lack of experience flying in winter weather conditions.” 

Weather at the time of the accident was reported as calm winds, a low overcast layer at 900 feet, 1.25-mile visibility with light snow and mist, and a temperature of -1 degrees C with a dewpoint of -2 degrees C. 

According to the report, the aircraft was on the ground for approximately 50 minutes while it was being refueled and passengers loaded. Personnel from the FBO and a lineman that was deicing another aircraft stated that the accident flight crewmembers did not request deicing services and that none were provided. 

One of the surviving passengers reported that during taxi-out, slushy clumps of snow and water slid down the side of the fuselage. The other surviving passenger stated that water ran off the skin of the airplane, “like it had taken a shower.”  

According to the CVR transcripts, pilots planned a “performance takeoff.” Approximately 30 seconds after setting takeoff thrust the first officer announced “V1” then “rotate.” Moments later as the aircraft began its initial climb, the stick pusher horn activated followed by the mechanical voice stating, “bank angle.” The recording ended less than 45 seconds after the application of takeoff thrust. 

Analysis of the accident flight indicated that the aircraft climbed to 20 to 50 feet, banked abruptly left, then right, and then left again before hitting the ground. 

Recent accident reports continue to suggest that pilots do not fully understand the concept of the clean aircraft concept or have a solid plan to deice or anti-ice an aircraft when conditions warrant.

In the first case, a Pilatus PC-12 crashed shortly after takeoff in low IMC conditions and moderate snow at Chamberlain Municipal Airport in South Dakota on November 30, 2019. The NTSB final report, published in May, listed a loss of control after takeoff, resulting in an aerodynamic stall as the probable cause.

Contributing to the crash was the pilot’s improper loading of the airplane. The aircraft was not only overloaded with an extreme aft c.g., but there were 12 occupants in an aircraft with only 10 seats.

Additional details in the report highlighted a persistent period of light to moderate freezing drizzle and snow in the 24-hour period before the accident. The pilot reportedly bought isopropyl alcohol at a local hardware store and worked for about three hours to remove snow and ice from the aircraft. A seven-foot-tall ladder that was available was not tall enough to reach the top of the aircraft’s tail. 

According to a witness, the pilot stated that “the airplane was 98 percent good, and the remaining ice would come off during takeoff.” The same witness recalled it was snowing “hard” when the pilot took off.

A study of photos and video footage recorded as the aircraft began to taxi for takeoff revealed that snow had accumulated on the upper surface of the horizontal stabilizer with icicles on the horizontal stabilizer bullet fairing. 

Data from the lightweight data recorder (LDR) indicated that the aircraft reached a peak altitude of 380 feet agl after takeoff with a maximum bank angle of 64-degrees. At that point, the airspeed decreased to 80 knots and the stall warning and stick shaker became active for the remainder of the flight.

The crash site was located less than three-quarters of a mile from the airport—the pilot and eight passengers were killed; the three remaining passengers were severely injured. 

A more recent accident occurred on January 2 at Provo (Utah) Municipal Airport (KPVU). In this accident, an Embraer Phenom 300 was substantially damaged during an attempted takeoff. The pilot was killed, while the three passengers were injured. 

According to witnesses, the aircraft was observed to takeoff and climb to about 20 to 30 feet agl and then the wings began to wobble “back-and-forth.” The aircraft then banked right and then “hard left” as the left wing struck the ground. Upon impact, the wings and engines separated from the fuselage. 

Of importance, only the NTSB preliminary has been published and the probable cause of the accident has not been determined. However, this report provides additional insight into an event where there was an opportunity to deice an aircraft before takeoff. 

In this case, the aircraft was removed from a heated hanger at 10:55 a.m. local. Shortly afterward, the fueler began to fuel the aircraft and noted unfrozen water droplets on the wing. Once fueled, the pilot boarded the aircraft and started the engines.

The aircraft began its takeoff roll at 11:35 a.m., when witnesses observed light to moderate snow and misty rain falling on the airport. The temperature and dewpoint at the time of the accident were both -1 degree C.

Clean Aircraft Concept

According to the FAA—specifically FAR 121.629, 125.221, 135.227, and 91.527—the clean aircraft concept prohibits takeoff when snow, ice, or frost is adhering to wings, propellers, or control surfaces of an aircraft. 

The FAA warns, “The degradation in aircraft performance and changes in flight characteristics when frozen contaminants are present are wide ranging, unpredictable, and highly dependent upon individual aircraft design. The magnitude of these effects can be significant. It is imperative that takeoff not be attempted unless the pilot in command (PIC) has made certain, as required by the FAR, that all critical areas of the aircraft are free of ice, snow, and frost formations.”

FAA Advisory Circular AC 135-17, “A pilot guide for small aircraft deicing,” reminds pilots that “to achieve compliance with the clean aircraft concept, it is imperative that takeoff not be attempted in any aircraft unless the PIC is certain that critical components of the aircraft are free of frozen contaminants. The revised rules in Parts 121, 125, and 135 of the FAR are intended to achieve implementation of the clean aircraft concept. The new regulations require that the operator develop specific procedures for the PIC. Those procedures may require having, in place, specific procedures, qualified personnel, and adequate equipment, and supplies.”

Furthermore, FAA Advisory Circular AC 20-117 is an additional resource that provides general information for the basic understanding of aircraft ground deicing issues and philosophy, including the definition of frozen contaminants and how they can affect aircraft performance and flight characteristics. 

Bottom line: the clean aircraft concept is essential to safe flight operations. The PIC has the ultimate responsibility to determine if the aircraft is clean and that the aircraft is in a condition for safe flight.

A good “rule of thumb” to ensure compliance with the clean aircraft concept is to deice the aircraft any time there are frozen contaminants on any of the critical surfaces and to prepare for and treat the aircraft with anti-ice fluids whenever local weather observations (or the pilot visually observes) any freezing or frozen precipitation.

The opinions expressed in this column are those of the author and not necessarily endorsed by AIN Media Group.