On an unknown date at an unknown time, a Bombardier DHC-8-200, N367PH, fuselage tail section was substantially damaged. The damage was found during a maintenance C-check inspection on August 29, 2009. The airplane was operated by Champlain Enterprises, Inc. d.b.a. CommutAir Airlines as a Continental Airlines connection flight under the provisions of Title 14 Code of Federal Regulations Part 121. Since it could not be determined as to the date or time of the accident, the occurrence date was the date in which the damage was found.

The skin, rivets, and the center former of the aft pressure bulkhead were damaged. The damaged section was located between stations 545.00 and 600.00 with the concentrated damage located between stations 565.50 and 580.50 along the longitudinal axis and between stations 31 right hand and 31 left hand along the lateral axis on the fuselage. The damage was located aft of the point where the empennage begins to curve up, and forward of the tail skid (bumper), which according to maintenance personnel was undamaged. The area of damage was located on the belly of the aircraft. The height of station 545.00 was approximately 30 inches above the ground and the height of station 600.00 was approximately 40 inches above the ground. The damage was consistent with tail strike damage during operation of the airplane and had resulted in a puncture of the pressure vessel of the airplane. The damage was found when maintenance personnel were inspecting the inside of the tail section. They noticed bowing and bending in the support structure and damage to nearby rivets. Further inspection of the exterior of the airplane revealed the skin damage.

According to the airline's maintenance line check form "General Exterior Walkaround," which was utilized for all "L" inspections, maintenance personnel were required to "Perform exterior walk around inspection of aircraft for, but not limited to; leaks, obvious impact damage/foreign object damage, structural irregularities… (5) Underside of fuselage paying particular attention to drain holes, antennas and tail skid (bumper)."

The operator's DHC-8-200 Series Service Check form stated in part "Exterior Walkaround Inspection. Perform an exterior walk around inspection of the aircraft for any of the following conditions which can be viewed from the ground…B. Obvious impact damage, C. Foreign Object Damage (FOD). D. Structural irregularities…F. Loose or damaged panels, latches, and fasteners."

According to the airline's maintenance DHC-8-200 Series Q Task Work Card "Heavy check pre-wash walk around inspection of the aircraft" Section 5: "Perform a visual inspection of the aft fuselage and tail for obvious damage, leaks, and loose fasteners viewed from the ground pay particular attention to the following:
A. Cargo door
B. Aft fuselage skin panels
C. Leading edges and skin panels of stabilizers
D. Rudder and elevators"

The DHC-8 Aircraft Operations Manual, Section 3 "Flight Preparation" stated in part "Before the first flight of the day for the crew. The SIC [Second-in-Command] will complete the first flight of the day preflight inspection duties… Before every flight. The SIC will complete all applicable preflight inspection procedure…" "Preflight Inspection Procedures" stated in part "First flight of the day preflight. This preflight inspection will be performed prior to the aircraft first flight of the day. It consists of the[sic] performing the following checklist…Exterior Preflight Flow." The section goes on to further require that when performing an aircraft acceptance preflight, turn-around preflight-after terminating checklist, and turn-around preflight-quick turn that the "Abbreviated Exterior Preflight" checklist will be utilized. The "Exterior Preflight Flow" stated in part "Empennage…Tail Cone Condition…" The "Abbreviated Exterior Preflight" stated in part "The PIC [Pilot-In-Command] will normally accomplish the walk-around, but it may be delegated to the SIC. The items to be checked include…Tail Skid…"

The multi-engine turboprop airplane was issued a transport category airworthiness certificate on December 2, 1998. According to airline maintenance records the airframe had accumulated 23,846.5 total hours of time in service and 33,868 total airframe cycles at the time of the maintenance inspection. The three most recent "L" inspections that the airplane had undergone were complied with on August 7, 2009, August 14, 2009, and August 21, 2009. Service checks were performed on the airplane each day the airplane was operated in revenue service including the days of the "L" inspections.

The airline had interviewed four sets of flight crewmembers that flew the airplane two days prior to its maintenance inspection and none of the crewmembers reported to airline personnel any tail strike events. Nor had there been any reported towing events reported to the airline from ground support personnel.

The flight data recorder was sent to the NTSB Vehicle Recorders Laboratory and downloaded. The download consisted of 23 flights and a review of all of those flights revealed several flights with an angle of attack of 7.5 degrees or greater during landing. However, no flight was located with an angle of attack in close proximity of the ground which could have resulted in a tail strike.

A representative of the airplane manufacturer reported that if the gear had been inadvertently retracted while in close proximity of the ground, the angle of attack would need to exceed 3.69 degrees in order to strike the tail section of the airplane. Although several flights exceeded that angle of attack it could not be determined what position the gear handle was in at the time of the exceedance.

According to documentation provided by the airplane manufacturer, the aft fuselage contact angle in a similar airplane would be 12.5 degrees with the landing gear struts fully extended and with zero runway crown. If the landing gear struts were fully compressed then the aft fuselage contact angle would be approximately 9.3 degrees with zero runway crown and with touchdown rates of descent exceeding 10 feet per second

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