Finding from 2005 accident investigations alerts board to deficiencies in aircraft’s cold-weather procedures
Immediate action to reduce the risk of icing accidents involving the Cessna 208 Caravan has been demanded by the US National Transportation Safety Board. The board has issued urgent recommendations to raise the minimum airspeed in icing, prohibit flight into more than light icing and require pilots to disengage the autopilot and fly manually in icing conditions.
The NTSB’s demand is based on preliminary findings of investigations into two Cessna 208B fatal crashes last year, in Winnipeg, Canada on 6 October and Moscow, Russia on 19 November. The board is “very concerned” about deficiencies in cold-weather operational procedures and aircraft performance in icing, concerns it says are shared by investigators in Canada and Russia.
In 2004, an NTSB review of Caravan icing accidents produced a series of recommendations that resulted in US Federal Aviation Administration airworthiness directives requiring tactile checks of the wing for icing, and installation of de-icing boots on the cargo pod and landing-gear fairings.
Cessna is working with the FAA and NTSB, but says the Caravan is safe “when flown in accordance with the flight manual”. The company faces several lawsuits related to Caravan crashes in icing conditions, but won a trial in Alaska in November when the jury determined there was no design flaw.
In the Canadian accident, the Morning Star Air Express aircraft (C-FEXS) crashed 5min after take-off from Winnipeg airport and 3min after the pilot informed air traffic control she needed to return because of icing conditions. The board is concerned the aircraft did not maintain flight in what is believed to have been moderate icing long enough to land.
In the Moscow accident, the aircraft (P4-OIN) crashed on approach to Domededovo airport, killing all eight on board. Cockpit voice and flight data recorders, fitted to comply with Russian certification requirements, show the aircraft stalled and crashed when airspeed slowed from 120kt (222km/h) to 102kt within 9min of entering icing characterised as moderate. The aircraft was on autopilot, and the NTSB is concerned this masked the aerodynamic effects of icing.
As a result, the board urges that the minimum operating airspeed in icing be increased from the 105kt in the flight manual to the 120kt limit used by Cessna test pilots. The NTSB also wants the FAA to prohibit Caravans from flying into anything more than light icing, and to require pilots to fly manually when in icing conditions.
GRAHAM WARWICK / WASHINGTON DC
Source: Flight International
