Service Difficulty Advisory
22 September 1999
De Havilland DHC 8 300 Series
Emergency Exit Type I Door
A recent Service Difficulty Report indicated that the flight crew and passengers had had a bad day. After landing on the last leg, the crew could not get the main airstair door open as the assist cable kept snagging on itself. An attempt was then made to deplane the passengers through the forward emergency exit. Unfortunately, it would not open either and appeared to be frozen in place.
The main door cables and struts were replaced. However, this advisory is about the emergency exit P/N 85220283001. This is the second occurrence of the problem in recent months for the submitter. Bombardier is attempting to resolve the situation. It is likely that this door issue will be a subject for their next ISAR.
The forward emergency exit is a door that is not used often, and may only be checked at inspection. Transport Canada recommends that operators who may have had problems with this door in the past send in SDRs. Whether the service difficulties have been found during inspection or operation, SDRs will provide a better picture of in-service difficulties with the emergency door.
This service difficulty with the Type I emergency door apparently occurs only on the 300 Series aircraft. Initial investigation by the submitter indicates that the problem may be associated with substantial amounts of moisture having pooled inside the door and freezing. This water may have collected at the cam, frozen while the door was at normal altitude, then jammed the door internal linkage for the handle. The submitter suggests the insulation blanket may be trapping the moisture and allowing it to drop onto the cam and roller.
With the door laid out full length on a bench there was pooling of water in low areas. Condensation was found on both the insulation blankets and the structure of the door. In addition, a large amount of ice was observed both free and within the blankets. The submitter notes that without considerable time to thaw, the ice prevented the water from draining away (impossible considering the type of operation). The aft lower external cam was found seized and the forward lower roller was stiff. The operating cam spigot also had some small amount of moisture on it. There was no corrosion and the seal valve was found serviceable.
The submitter concluded that water in this door is not unusual and winter operations do not allow enough time for any formed ice to melt. Water can collect in the operating cam with the door at normal attitude. Although moisture has not been proven to be the cause, it remains the prime area at this time for corrective action. The submitter has instituted a temporarysupplemental inspection and lubrication of this emergency door. This will include increasing the frequency of the door functional check from the 5A Check to every A Check, in other words, from 2500 hours to 500 hours. In addition, they will increase the frequency of the door internal inspection from 5000 hours to 2500 hours.
Service Bulletin 8-52-35 dated April 1995, which provides instructions for the addition of drains had been complied with in November 1995. A new Service Bulletin, 8-25-145 dated 16 August 1999 has just been released. It provides for the installation of waterproof insulation around the door.
In the meantime the operator and the manufacturer are working together to solve the problem.
For more information please contact a Transport Canada Centre, or Mr. Peter von Moos, Continuing Airworthiness, Ottawa, telephone (613) 952-4428, facsimile (613) 996-9178 or e-mail firstname.lastname@example.org.
For Director, National Aircraft Certification
Chief, Continuing Airworthiness
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