Ice on wings becomes main focus in Montana crash

WASHINGTON (AP) Speculation over the crash of a single-engine turboprop plane into a cemetery shifted to ice on the wings Monday after it became less likely that overloading was to blame, given that half of the 14 people on board were small children.

While descending Sunday in preparation for landing at the Bert Mooney Airport in Butte, Mont., the plane passed through a layer of air at about 1,500 feet that was conducive to icing because the temperatures were below freezing and the air "had 100 percent relative humidity or was saturated," according to, a forecasting service in State College, Pa.

The case for a thermic laser lance method of de-icing, both on the ground and in the air, is again apparent. What's needed is an integrated solution, one that's reliable and rides along with the airplane. The basic concept is for turboprops to have self-steerable cupolas, one above the nose and a second one beneath their radomes - with fields of view that can enable ongoing laser mensuration of icing thickness on ( and deformity of) aerodynamic surfaces and engine intakes/props. A follow-through de-icing "strike" with a heating "thermic" lance laser would dislodge ice build-ups symmetrically from wings, nacelles and empennage surfaces. Ultra-high density capacitor charging required to fire thermic lance lasers have been developed during the USAF's 747-mounted anti-missile laser weaponry program (see links to that proven capability here and  here).

Another plausible application of the thermic lance is for bird-strike deterrence. The laser (with cupolas now facing forward) sweeps ahead through a narrow swathe above and below (as well as left and right) of the aircraft's track. Birds constituting a threat along the flight-path would generate two instantaneous automated reactions:

a.  The aircraft would self initiate a much higher momentary rate of climb (restricted to a 2g progressive pull-up) to clear the hazard. Most pax would still be strapped in below 10,000ft on climb/descent and flight attendants wouldn't suffer ankle-breaks from a 2g non-instantaneous positive "g" application.
b.  The thermic laser would zap the threat birds (individuals, but in a flock, restrict its zapping to those constituting the greater threat). The normal bird reaction to an airborne predator threat is to instantly (and invariably) peel off into a dive. The birds would survive and the aircraft would pass above and clear the threat. The lower altitude limit for safe operation would need to be determined (for take-off for example)







Environmental Benefits:

Think about all the many thousands of gallons of de-icing fluid that daily pours down the drains at major airports all over the world. Perhaps it's a ground de-icing and airborne solution for more than just turboprops. Perhaps there's also a cost/benefit equation in play here for savings on that volume of fluids flushed away in both original de-icing and aircraft that have to be "revisited" for exceeding their on-ground "hold-over time" (i.e. the max time an aircraft can spend in a queue before having to return to the ramp for a second de-icing).

Safety experts said similar icing condition existed when a Continental Airlines twin-engine turboprop crashed into a home near Buffalo Niagara International Airport last month, killing 50.

A possible aerodynamic stall in which ice causes the plane to lose lift, and the pilot's reaction to it, has been the focus of the Buffalo investigation.

"It's Buffalo all over again, or it could be," said John Goglia, a former member of the National Transportation Safety Board. "Icing, given those conditions, is certainly going to be high on the list of things to look at for the investigators."

Mark Rosenker, acting NTSB chairman, told reporters in Montana that investigators would look at icing on the wings as a factor.

"We will be looking at everything as it relates to the weather," he said.

The plane, designed to carry 10 people, crashed 500 feet short of the Montana airport runway Sunday, nose-diving into a cemetery and killing seven adults and seven children aboard. Relatives said the victims were headed to an exclusive resort on a ski vacation, and gave the children's ages as 1, 3, 5, 7 and 9, plus two 4-year-olds.

Safety experts said finding the cause of the crash is likely to be significantly complicated by the absence of either a cockpit voice recorder or a flight data recorder, which isn't required for smaller aircraft that don't fly commercial passengers like airlines and charter services.

Former NTSB chairman Jim Hall pointed to similarities between the Montana crash and a March 26, 2005 crash near Bellefonte, Pa., in which a pilot and five passengers were killed.

The plane in both cases was the Pilatus PC 12/45 and was on approach to an airport. In both cases there were reports of conditions conducive to icing at lower elevations and witness reports that the plane appeared to dive into the ground.

"I'm certain they are also going to look at the weather conditions at the time and the pilot's training," Hall said. He pointed to a recommendation on NTSB's "most wanted list" of safety improvements that FAA test the ability of turboprop planes to withstand a particular type of icing condition called "super cooled liquid drops" before certifying the aircraft design for flight. FAA officials have said they're working on that recommendation.

"If you had some precipitation and the temperature was in the right range, that again is an area that investigators would look at," Hall said.

NTSB investigators, local police and members of the sheriff department investigate the scene of fatal plane crash outside the Butte Airport in Butte, Mont., on Sunday, March 22, 2009. A small plane, possibly carrying children on a ski trip, crashed Sunday as it approached the Butte airport, killing 14 to 17 people aboard, according to a federal official. The single engine turboprop nose-dived into a cemetery 500 feet (150 meters) from its destination.

Hours after the crash, federal investigators had focused on overloading as a possible cause.

"It will take us a while to understand," Rosenker said. "We have to get the weights of all the passengers, we have to get the weight of the fuel, all of the luggage."

Goglia said the Pilatus has a powerful engine for its size and is unlikely to be affected by the additional weight of a few children "unless they had an awful lot of baggage."

Standard flight procedures are for the pilot to file a report on the plane's weight, including the weight of the passengers and the baggage and how that weight would be distributed around the plane, before taking off, safety experts said.

Federal Aviation Administration certification records for the Pilataus PC-12-47, the type of plane that crashed, give the aircraft's maximum landing weight as 9,921 pounds, including a maximum baggage weight of 400 pounds stored in the baggage compartment at the rear of the cabin. The document doesn't specify a separate weight for passengers.

Peter Felsch, a meteorologist at the National Weather Service, said conditions measured on the ground not long after the 2:30 p.m. MDT crash were fair winds of about 9 mph, 10 miles visibility, a temperature of 44 degrees Fahrenheit and a "broken cloud deck at 6,500 feet."

The Pilatus PC 12/45 is certified for flight into known icing conditions, according to the manufacturers' Web site and pilots who have flown the plane.

However, like all turboprop planes, it relies on deicing boots strips of rubber-like material on the leading edge of the wings and the horizontal part of the tail that inflate and contract to break up ice. That technology, which goes back decades, isn't as effective at eliminating ice as the heat that jetliners divert from their engines to their wings.

One key in the Butte crash will be whether the pilot had changed the position of the aircraft's wing flaps for landing because changing the configuration of the wings by moving the flaps is where icing problems often show up, said Peter Goelz, a former NTSB managing director.

There won't be any radar data of the plane's final moments for investigators to examine like thousands of small airports, the Butte airport doesn't have a radar facility. The radar at the FAA's en route center in Salt Lake City, which handled the flight's last leg, doesn't extend as far as the Butte airport because of the mountains between.

The last radio communication from the turboprop's pilot was with the Salt Lake City Center when the plane was about 12 miles from Butte,

The plane crash that killed all seven children and seven adults on board began with a sudden nose dive just short of the airport in Butte, a federal official said.

National Transportation Safety Board Acting Chairman Mark Rosenker said his team is looking into the experience of the pilot and whether the 11-seat plane was overweight. The single-engine plane had no "black box" flight data recorder and the investigation could take months.

The Pilatus PC-12 turboprop plane was carrying three fewer passengers than originally reported on Monday and if infants were being carried on laps, the entire group could have fit on board.

The plane made three stops in California before heading to Bozeman, Montana, for a ski vacation but officials did not give details about the passengers. Bozeman and Butte are towns of about 30,000 each in the mountainous western half of the state.

The single pilot requested twice to divert to Butte from Bozeman, without giving a reason, and both times the Salt Lake City flight controller approved the change, Rosenker told a news conference.

He said witnesses saw the plane flying at about 300 feet and take a 90-degree nose-dive before crashing in a cemetery just short of the airport. Photos showed a ball of flame at the crash site.

See: "Super-cool" - the Short-cut to Cryogenic death



 said Doug Church, a spokesman for the National Air Traffic Controllers Association. The pilot told controllers he intended to land at Butte using visual landing procedures rather than relying on instruments, which is not unusual, Church said.

Rosenker confirmed that the pilot said nothing to controllers to indicate he was having trouble, including during radio conversations earlier in the flight when the pilot notified controllers he intended to divert from the flight's original destination of Bozeman, Mont., to Butte.

"We don't know the reason for the requested change to the flight plan," Church said. "We don't know whether weather was a factor in Bozeman. There was no apparent reason given for the change in flight plan from Bozeman to Butte."

John Cox, an aviation safety consultant and former crash investigator for the Air Line Pilots Association, said the lack of data means investigators will have to go "back to the old, traditional way of investigating aircraft accidents, looking at impact angles, looking at damage done to the aircraft, whether the engine was producing power or not."

"Then they'll have to look for anything unusual bird feathers, a piece missing off the engine it will be a series of exclusions," Cox said. "It will be sketchy, and it will not be nearly as definitive as it would be if they had had one of the recorders."

The particular plane that crashed Sunday was registered to Eagle Cap Leasing Inc. in Enterprise, Ore. It wasn't listed on any air carrier's operating specifications and therefore couldn't carry passengers for hire, but that wouldn't preclude leasing, FAA spokesman Les Dorr said.

The unrecognized problem with turboprop icing is the asymmetric distribution of ice along fuselage, wings and empennage caused by both props rotating in the same direction. This asymmetric icing build-up causes an asymmetric stall condition that will always lead to:
a. an overall much higher stall speed (that won't necessarily be detected by AoA vanes and so won't result in higher stick-shaker/stick-pusher actuation speeds)
b. An asymmetry between left and right wing stall speeds (that will always cause a fatal spin entry, especially at approach speeds).

c. Any pilot's natural reaction will be to try and "pick up" a dropped wing with aileron. This action will invariably embed that wing into its stalled condition and accelerate auto-rotation (i.e. spin entry).

The Unrecognized Hazard


FAA Issued Safety Directive on Montana Plane

Some Pilatus PC-12s Had Problem That Could Reduce Effectiveness of the Controls

Just 12 days before the fatal crash of a Pilatus PC-12 killed 14 people in Montana, the Federal Aviation Administration issued an airworthiness directive on the plane, requiring that a safety inspection be performed to check for a problem that could reduce the effectiveness of the plane's controls.

FAA Issued Safety Directive on Montana Plane

Just 12 days before the fatal crash of a Pilatus PC-12 killed 14 people in Montana, the Federal Aviation Administration issued an airworthiness directive on the plane, requiring that a safety inspection be performed to check for a problem that could reduce the effectiveness of the plane's controls.

The directive is not effective until March 30th, at which date the owner would be required to do the inspection within 150 flight hours.

Prior to the FAA directive, the plane's manufacturer sent out a service bulletin in January and the European Aviation Safety Agency issued its own directive in late February, regarding potential problems with the plan's stick-pusher.

Mark Rosenker, acting chairman of the NTSB, said at briefing on Tuesday that the stick-pusher and its cables were located at the crash site fully intact and that investigators did not see any problems. It is still unclear if the plane's owners had already conducted their inspection and if any problems had to be corrected, NTSB investigators continue to examine the maintenance records of the plane.

At issue, according to the directives, are occurrences where the rear stick-pusher cable clamp shifted forward on the elevator cable.

"This condition," said the directive, "if not corrected, may reduce the effectiveness of the stick-pusher and/or limit elevator control movement." The directive calls for an inspection of the stick-pusher cables.

ABC News aviation consultant John Nance explains that the stick pusher is a built-in backup mechanism that will help the pilot if he or she cannot or has not recovered from an impending stall. In some cases, the stick-pusher acts as a "last ditch effort" to save the plane.

In the case of Sunday's crash less than a mile from the runway in Butte, the plane banked at a sharp angle before nose-diving into a cemetery, killing everyone onboard. The investigation into the cause has been complicated by the fact that the plane did not have any flight data or voice recorders.

see also this link

Related articles