Uncontained APU Turbine Failure During Deicing (N1426A)

Incident Overview and Damage Assessment During a deicing operation, the aircraft's auxiliary power unit (APU) ingested deicing fluid and snow, leading to an uncontained turbine failure. The incident resulted in minor damage to the pressure bulkhead. All four crew members and 40 passengers on board were uninjured. The specific aircraft type, registration, operator, date, and location are not provided in the source material. ## Weather Conditions at YUL At the time of the incident, the weather at YUL was reported as follows: wind from 050 degrees at 25 knots, gusting to 33 knots; visibility of 15 statute miles; drifting snow; a broken cloud layer at 2,800 feet and an overcast layer at 7,600 feet; a temperature of -1 degree Celsius; a dew point of -5 degrees Celsius; and an altimeter setting of 29.57 inches of mercury. ## Technical Findings and Maintenance Advisories A teardown inspection of the Honeywell APU revealed evidence of an engine overspeed event with a commanded auto-shutdown in the Electronic Control Unit (ECU) non-volatile memory. The investigation report noted that in February 2001, American Airlines issued a 'Winterization Bulletin' for the F-100, advising that de-ice spray should not be directed into the APU inlet. Furthermore, the Fokker 100 maintenance manual, section 12-31-00, page 301, specifically states: 'Do not let de-icing and/or anti-icing fluid/water mixture go into the APU inlet. Injury to persons and/or damage to equipment can occur.'