Introduction
On August 29, 2009, during a scheduled C-check maintenance inspection, personnel discovered damage to the fuselage tail section of a Bombardier DHC-8-200, registration N367PH. The aircraft was operated by Champlain Enterprises, Inc., doing business as CommutAir Airlines, flying as a Continental Airlines connection under 14 CFR Part 121. The date and time of the occurrence could not be determined; the discovery date was used as the event date.
Damage Details
The damage affected the skin, rivets, and center former of the aft pressure bulkhead, located between stations 545.00 and 600.00 along the longitudinal axis, with concentrated damage between stations 565.50 and 580.50. Laterally, the damage spanned stations 31 right hand to 31 left hand on the fuselage belly. The area was aft of the empennage curve and forward of the undamaged tail skid (bumper). The height of station 545.00 was approximately 30 inches above the ground; station 600.00 was approximately 40 inches above the ground. The damage was consistent with a tail strike during operation and resulted in a puncture of the pressure vessel. Maintenance personnel first noticed bowing and bending in the support structure and damaged rivets during an internal inspection; external inspection confirmed skin damage.
Inspection Procedures
The airline's maintenance line check form "General Exterior Walkaround" required personnel to visually inspect the underside of the fuselage, paying particular attention to drain holes, antennas, and the tail skid. The DHC-8-200 Series Service Check form similarly required a walkaround to check for obvious impact damage, foreign object damage, structural irregularities, and loose panels. The heavy check pre-wash walkaround work card specified visual inspection of the aft fuselage and tail for damage, leaks, and loose fasteners. The aircraft operations manual required preflight inspections including the empennage and tail cone condition; the abbreviated exterior preflight checklist included checking the tail skid.
Operational History
The aircraft was issued a transport category airworthiness certificate on December 2, 1998. At the time of the inspection, it had accumulated 23,846.5 total hours and 33,868 cycles. The three most recent "L" inspections were performed on August 7, 14, and 21, 2009. Service checks were performed daily when the aircraft was in revenue service. The airline interviewed four flight crews who operated the aircraft in the two days prior to the C-check; none reported a tail strike event. No towing events were reported by ground personnel.
Flight Data Analysis
The flight data recorder was downloaded by the NTSB, providing 23 flights. Review showed several flights with an angle of attack (AoA) of 7.5 degrees or greater during landing, but no flight had an AoA in close proximity to the ground that could have resulted in a tail strike. A manufacturer representative stated that if the landing gear were inadvertently retracted near the ground, a tail strike would require an AoA exceeding 3.69 degrees. Although several flights exceeded that angle, the gear handle position at those times could not be determined. The manufacturer also noted that for a similar aircraft, the aft fuselage contact angle with gear fully extended and zero runway crown is 12.5 degrees; with gear fully compressed and a descent rate over 10 feet per second, the contact angle is approximately 9.3 degrees.