Directorate of Assessments and Prevention
Aviation Division
U.S. Army Combat Readiness Center
Fort Rucker, Alabama

In the five-year-plus period of fiscal 2013 through June 2018 (1,033,833 flight hours), 74 Class A-C AH-64 mishaps were recorded. Of those, 65 had identified or suspected cause factors.

Nine of the mishaps had unknown or not yet reported cause factors. A breakdown shows there were 21 Class A mishaps (18 flight, one flight-related and two aircraft ground); 14 Class B (13 flight, one flight-related); and 39 Class C (30 flight, four flight-related, five aircraft ground). There were 14 Army fatalities and a cumulative mishap cost of more than $427 million. The Class A flight mishap rate per 100,000 hours was 1.74. Class A-C rate was 7.16. A review shows human error was the primary cause factor in 50 (76.9 percent) of the mishaps with a reported cause factor in 13 (20 percent) materiel failures; and 3.1 percent environmental related.
The following is a breakdown of mishap event types:

Object Strikes
Object strikes account for nearly 36.3 percent of the Class A and 24 percent of the total Class A-C mishaps. There were eight tree strikes recorded in the 74 incidents, five resulting in Class A and B damage. Other types of object strikes included three wire strikes (two Class A, one Class C); three ground taxi/aircraft run-up incidents (two Class A, one Class B); and seven incidents involving striking the ground (three Class A, two Class B, two Class C). Examples of object strike mishaps include:

Scenario 1
The aircraft was Chalk 2 in a flight of two, conducting mission training when it descended into a wooded area and crashed. The crewmembers were extracted with treatable injuries, and the aircraft was reported as destroyed. (Class A)

Scenario 2
While conducting night vision system (NVS) confined area operations, the aircraft drifted into trees. The aircraft came to rest on its side with potential Class A damage. (potential Class A)

Scenario 3
The aircraft contacted a ground obstacle during a movement-to-contact maneuver. The crew subsequently executed a controlled landing. (Class A)

Scenario 4
The crew was executing an approach to mountainous terrain in conjunction with readiness level progression training. The aircraft’s tail wheel contacted the edge of the terrain shelf that comprised the designated landing area. (Class C)

Power management
Power management/aggressive flight maneuvering was involved in five of the Class A and B mishaps for the five-plus-year time period. There were also three Class C incidents. Summaries of some of the power management mishaps include:

Scenario 1
The crew reportedly experienced a tailwind and airspeed/rotor droop once airborne from refuel, followed by loss of tail rotor effectiveness. The aircraft descended to ground impact, rolled and came to rest on its left side. The crew was able to egress with minor/superficial injuries. (Class A)

Scenario 2
The aircraft, as trail in a flight of two, lost altitude while on final approach at approximately 100 feet above ground level (AGL) and contacted the ground with the tail wheel. The aircraft sustained damage to the tail and left main landing struts and the gun turret and rear airframe mounts. (Class B)

Scenario 3
The crewmembers experienced a low-rotor warning as they were repositioning on the taxiway for incoming aircraft while performing a HIT check. (Class C)

Maintenance error
There were three (one Class A, two Class B) human error mishaps involving incorrect/ incomplete procedures being followed during aircraft maintenance. Summaries of some of the maintenance error mishaps include:

Scenario 1
While reinstalling the No. 5 tail rotor driveshaft, the bolts were not properly torqued and subsequent inspections failed to identify the problem. Consequently, the No. 5 tail rotor driveshaft vibrated and caused the aft hanger bearing coupling to shear, resulting in the loss of tail rotor thrust. The aircraft landed hard with damage. (Class B)

Scenario 2
The crew reportedly experienced a loud report, followed by a nose-down pitch and right yaw of the aircraft during flight. The crew executed an emergency landing to an open field. A post-landing inspection revealed the tail rotor came off in flight due to incorrect torque procedures conducted on the tail rotor retention bolts. (Class B)

Scenario 3
While in flight, the aircraft experienced a catastrophic failure of the main rotor system and crashed, resulting in two fatalities. (Class A)

Materiel failure
Materiel failure was the primary cause factor in 13 (17.6 percent) of the Class A-C mishaps with reported cause factors. Summaries of some of the materiel failure mishaps include:

Scenario 1
The crewmembers were participating in night operations when they detected a smoke odor in the cockpit caused by a No. 2 generator bearing failure. While conducting an emergency landing, the crew experienced an electric power outage in the cockpit and loss of night vision systems. During the unaided landing to a dusty environment, the main rotor blades contacted the ground and the aircraft came to a rest on its side. (Class A)

Scenario 2
Crew had just completed ‘hot’ refuel and were at approximately 100FT AGL when they noted a loud report from the #2 engine area, followed by a LOW ROTOR audio indication. Aircraft touched down ‘hard’ as the crew attempted to land the aircraft on a firing pad. (Class A)

Scenario 3
The pin assembly securing a main rotor blade to the main rotor head sheared, causing catastrophic failure of the main rotor system. The aircraft crashed, resulting in two fatalities. (Class A)

Scenario 4
The aircraft’s lateral servo actuator malfunctioned due to suspected contaminants in the hydraulic system. This resulted in the lateral servo actuator back driving the flight controls through the mechanical control input connected to the servo. As a result, the cyclic moved uncommanded to the left, rolling the aircraft approximately 60 degrees and causing an impact with the ground. The aircraft was destroyed with no significant injuries to the crew. (Class A)

Scenario 5
Failure of the outboard strap pack bolt retainer nut resulted in the failure of the strap pack assembly and loss of the main rotor blades. The aircraft crashed, resulting in two fatalities. (Class A)

Scenario 6
The crew reportedly experienced aircraft anomalies during takeoff, followed by a No. 1 Engine-Out indication. Upon landing, the No. 1 engine TGT reading was at 999°C, and No. 2 engine indicated a torque-exceedance reading (125 percent> <130 percent). (Class C)

Scenario 7
The crew reportedly experienced a torque split and high TGT indication exceedance on the No. 1 engine while on approach. The crew landed the aircraft and, upon shutdown, identified an engine No. 1 NG overspeed >102.2. (Class C)

Other
Scenario 1
The crew chief came out to recover the aircraft and observed the nacelle door open. He noticed both handles were extended in the open position and indicated to the pilots the door was open as they shut down. (Class C)

Scenario 2
After the flight was completed, the crew conducted a post-flight inspection and discovered a missing panel and damage to two main rotor blades and a tail rotor blade. (Class C)

Scenario 3
A post-maintenance test flight revealed metal debris on the transmission deck as residual damage from in-flight separation of a torque tube from its mounts. (Class C)

Scenario 4
The aircraft start-up was attempted with the No. 2 engine inlet plug still in place. Inspection criteria required engine replacement. (Class C)

Scenario 5
Six rotor blades stacked outside the hangar blew over from a passing aircraft’s rotor wash, causing non-repairable damage to two blades.

Scenario 6
The crew of aircraft No. 1 was conducting assault training with a sister ship when it collided with another aircraft on a separate mission conducting aerial recon of an objective in the vicinity. Both aircraft crash-landed, and crewmembers suffered no significant injuries. (Class A)

Summary
Looking at the fiscal 2008-12 time period, the numbers remain generally consistent with the most recent time period. The AH-64 Class A-C mishap rate was 7.12 with 85 incidents versus the 7.16 rate with 74 mishaps for the latter time frame. Mishap types are also similar, with object strikes, overspeed/overtemp/overtorque and power management events as the most prominent. Typically in manned aviation mishaps, human error is the primary contributing factor in 75-80 percent of mishaps.

Whether operating or maintaining the aircraft, strict adherence to established standards and procedures, coupled with good supervision, remains the most effective countermeasure in the reduction of human error mishaps.