FAA searches for solution to Caravan icing accidents

 - September 20, 2006, 10:15 AM

Concerned about the growing number of Cessna 208 Caravan icing accidents, aviation authorities in the U.S. and Canada have issued a bevy of new recommendations, airworthiness directives and restrictions. Caravans continue to be plagued by icing accidents–more than 34 to date– and the number of lawsuits against the manufacturer is mounting.

The Caravan is considered a workhorse, used for overnight cargo hauling for carriers such as FedEx and United Parcel Service, as well as for medical and check-hauling operations by smaller entities. (FedEx and its contractors own and operate 264 Caravans; UPS contractors operate 44.) These missions do not lend themselves to no-go decisions and are frequently flown by young, inexperienced pilots.

In 2003 the NTSB studied 26 icing-related accidents and incidents resulting in 36 fatalities between 1987 and 2003. In 15 cases, ice accumulated while the airplane was in flight, during approach and landing. In 10, ice accumulated on the ground, before takeoff, and was not removed adequately. (There are no details on the 26th.) The NTSB said that most were in “flight in icing conditions that appeared to be within the parameters of the FAA’s icing-certification envelope.” Last April, the FAA recorded six accidents during the 2004 and 2005 icing season.

Two recent accidents have added to the authorities’ concern. On November 19 last year an Aruban-registered Caravan 208B, P4-OIN, crashed on approach to Moscow Domodedovo International Airport after the crew reported they had encountered icing conditions. The two pilots and six passengers were killed and the airplane destroyed.

The aircraft was equipped with a flight data recorder (FDR) and a cockpit voice recorder. Initial investigation by the Interstate Aviation Commission of Russia, with assistance from the NTSB, showed that the pilots, cruising at 9,840 feet on autopilot, were discussing severe icing only five minutes after they had reported to ATC they were not experiencing icing, which was forecast.

Cleared to descend for landing, the crew was reading the descent checklist about the time the FDR indicated the airplane pitched up as the airspeed began to decrease. At about 102 knots, the Caravan began to stall. The autopilot disengaged and the airplane descended with bank-angle excursions of plus or minus 40 degrees and reached 226 knots just before it hit the ground.

Authorities are also concerned about the Morning Star Air Express Caravan crash in Winnipeg last October, in which the pilot told ATC two minutes after takeoff that she needed to return to the airport because of icing. The airplane crashed three minutes later. Although the accident is still under investigation, witnesses have since reported that the ATP-rated pilot, who was killed, made a tactile examination of the wings for ice and frost during preflight.

After its 2003 study, the NTSB issued a recommendation (A-04-64 through -67) to the FAA in December 2004. The Caravan’s high wing “makes it difficult,” the recommendation said, for a pilot to see ice on the upper wing surface aft of the de-ice boots.

The recommendation further stated that the Pilot’s Operating Handbook warns
that an accumulation of one inch of ice on the leading edge can cause up to 500 fpm loss in rate of climb, a cruise-speed reduction of up to 40 kias and a significant buffet and stall speed increase of up to 20 knots. The POH also warns that the stall-warning horn may not function if one inch of ice has accumulated, and there may be little or no prestall buffet.

Operators told the NTSB that the Caravan pilot’s workload increases significantly in icing conditions because the pilot must constantly monitor the pneumatic boot
de-ice system.

Tactile Check of Wing Required
Last March, the FAA issued an AD (2005-07-01), prompted by “six accidents in the previous two icing seasons and nine events in the past few months” (and probably by the NTSB’s 2004 recommendations). Most of the accidents occurred on approach and landing, the FAA said, and one-third were suspected to involve supercooled large droplets, icing conditions that are outside the certification envelope.

The AD prohibited takeoff with any frost, ice, snow or slush adhering to the wings, horizontal stabilizer, control surfaces, propeller blades and engine inlets. It also required a pre-takeoff tactile and visual check of the wing leading edge, wing upper surface, horizontal-tail leading edge and propeller blades.

The check is required if the outside air temperature is less than 5 degrees C (41
degrees F) and visible moisture is present; if the airplane has been exposed to visible moisture since the previous landing; if it has accumulated ice since the previous takeoff; if the dew point-to-temperature difference is 3 degrees C (5 degrees F) or less; or if water is present on the wing.

This January, the FAA adopted a new Airworthiness Directive (2006-01-11) for the Caravan. Effective February 22, operators are required to install a pilot-assist handle to allow inspection of the upper surface of the wing and de-icing boots for the landing gear struts and cargo pod by June 27.

The new AD applies to Caravans already equipped with pneumatic de-icing boots. It does not apply to Caravans equipped with the TKS ice-protection system (see box on page 85). Operators also must install a placard stating that the airplane cannot be flown in known icing conditions if the new equipment is not added.

Inserting a copy of the AD satisfies required changes to the Pilot’s Operating Handbook and the airplane flight manual. Costs were originally estimated to be about $9,000 per aircraft (and the FAA said that 743 Caravans in the U.S. registry are affected), but that figure has increased to $14,434. The Regional Air Cargo Carrier Association, U.S. Parachute Association, the Alaska Air Carrier Association and Cessna Aircraft opposed the new AD.

Since the AD was issued, the NTSB recommended to the FAA that operators of Caravans be required to maintain 120 knots in icing conditions, even if a descent is required to do so; to prohibit flight into any icing conditions worse than light; and to require disengagement of the autopilot in icing conditions. The Board said the Russian accident showed that 102 knots should no longer be considered a safe airspeed in icing and that the pilots might have been able to react more quickly had they been flying manually.

On January 31 the Transportation Safety Board of Canada issued its recommendations, stating that Cessna 208s seem to be more significantly affected by atmospheric icing than other types of Cessna turboprops certified for flight in known icing. It cited 19 Caravan icing events between 1990 and 2005. The Canadian board recommendations were essentially the same as the NTSB’s.

At press time the FAA was considering further restrictions for Caravan operations. An agency spokesman said, “I would not be surprised if there were additional action.”
The FAA first officially recognized icing problems with the Caravan in 1996. The agency issued an AD (96-09-15), effective June 11 of that year, requiring operators to include information about recognizing and escaping icing conditions in airplane flight manuals. The agency estimated that 169 aircraft would be affected.

The 1996 AD stated that flight in freezing rain, freezing drizzle and mixed icing conditions might result in ice buildup on protected surfaces that exceeds the capability of the ice-protection system. The aircraft’s anti-icing system includes operational leading-edge de-ice boots on the wings and horizontal and vertical stabilizers, propeller anti-ice boots, windshield anti-ice panel, heated pitot-static and stall-warning systems, a standby electrical system, a wing ice-detection light and an engine inertial separator.

During flight in icing conditions, the AD continued, pilots should immediately request priority handling from ATC if unusually extensive ice accumulates on areas of the airframe that normally do not collect ice or if there is an accumulation of ice on the lower surface of the wing aft of the protected area. Pilots were prohibited from using the autopilot if they spotted ice in these areas.

Cessna Offers Cold-weather Training
In 1996, Cessna started offering a Caravan Safety Awareness Program for Caravan and other Cessna operators, covering cold-weather operations such as preflight de-icing procedures and operational tips about flying in and around icing conditions.

The program, according to Chad Martin, manager of pilot and maintenance training for Cessna, is free and available to all Cessna pilots. Martin said that some 300
to 350 pilots attend each year. Cessna takes the programs to some 20 locations all over the U.S. and Canada and this year expanded it to Mexico and Germany. Cessna will send the training materials to pilots who want to attend but are unable to.

Steve McNew, the Cessna training administrator who conducts the seminars along with Martin, told AIN that he finds it “interesting that the FAA requires endorsements for high-altitude flying and high-performance checkout but not for flight into known ice. So when does a pilot learn to fly in icing conditions?”

McNew added that “after the ATR icing accident in Roselawn, Ind., [in 1994] the FAA released numerous ADs against basically all booted aircraft that provided clear and concise procedures/operations…but still no training is required.” (The NTSB recommended that the FAA require all pilots and operators of 208s equipped for flight-into-known-icing conditions to undergo annual icing training, but the FAA has not acted on that recommendation.)

McNew said he tells seminar attendees, “There has never been a civilian airplane built that can withstand flight into continuous known icing under moderate or severe conditions,” and “it’s the pilot’s responsibility to recognize and exit those conditions.”

The NTSB found that only five of the pilots involved in the 26 incidents cited
in its 2004 recommendation had attended a Cessna safety seminar. The Board recommendation noted that the effectiveness of operators’ own cold-weather operations program varied widely. The NTSB interviewed 22 qualified Caravan pilots who worked for operators in different parts of Alaska and found that many displayed inadequate knowledge of Caravan operations in icing conditions. Six of the 22 interviewed were not aware that the Cessna 208 POH warns pilots not to operate into or out of airports where freezing rain or drizzle is reported, and several were unfamiliar with ground de-icing procedures and materials.

The recommendation concluded that Cessna and its operators should develop “effective operational strategies” and the FAA should verify that operators are using these strategies.

Cessna points out that there are 1,500 Caravans operating worldwide that have flown 8.6 million hours with a 98-percent dispatch rate. “When operated in accordance with the Pilot’s Operating Handbook,” said a spokeswoman, “they’re the safest airplane around.”