LAX08LA221

While performing air work during the instructional flight, the student attempted to increase engine power above idle, but upon pushing the throttle control knob forward, the engine's power did not increase. The certified flight instructor (CFI) verified that there was no change in engine power with movement of the throttle control, and he believed that the control had likely become disconnected from the carburetor. The CFI performed a forced landing on the nearby rough terrain. During landing, the airplane impacted a berm and nosed over. An examination of the airplane revealed the throttle control cable was in fact disconnected from its respective carburetor attachment fitting and undamaged. Also, the threaded portion of the cable's attachment end was found without damage. The jam nuts, which normally secure the throttle cable to the carburetor attachment fitting, were found tight against each other, but backed off from their designated location, and were not positioned close enough to the rod end to secure the cable to the carburetor throttle arm. The operator's mechanics were responsible for, and had performed, recent maintenance and inspections of the flight school's airplane. The accident airplane's last 100-hour inspection had been performed on July 3, 2008, 6 days prior to the accident. The security and condition of the engine control connections to the carburetor are part of this inspection.

On July 9, 2008, about 1646 Pacific daylight time, a Cessna 172RG, N9627B, experienced a partial loss of engine power about 3 miles east-southeast of Moorpark, California. The certified flight instructor (CFI) acquired the airplane's controls from his student who had been maneuvering the airplane, and he made a forced landing. During landing, the airplane impacted rough terrain, nosed over, and was substantially damaged. Both pilots sustained minor injuries. American Flyers, Santa Monica, California, operated the airplane under the provisions of 14 Code of Federal Regulations Part 91. The CFI held a commercial pilot certificate, and he was the assistant chief instructor for the flight school. The student held a private pilot certificate. At the time of the accident, the private pilot was undergoing the final flight phase check for a commercial pilot certificate under the Federal Aviation Administration (FAA) approved school's Part 141 examination authority. Visual meteorological conditions prevailed, and no flight plan had been filed. The local area instructional flight commenced from Santa Monica Municipal Airport, Santa Monica, about 1515.

The CFI reported to the National Transportation Safety Board investigator that he had directed the student to perform a ground reference maneuver (eights on pylons) over a field, and the student commenced a descent to 1,000 feet above ground level. When the student attempted to increase the engine's throttle to level out, the engine's power did not increase. The CFI verified the problem and decided to execute an emergency landing. He set the transponder to the 7700 squawk code and attempted to declare an emergency to a nearby air traffic control (ATC) facility. The CFI stated that due to the airplane's low altitude, the radio transmission was not heard by ATC, but another airplane's pilot relayed the distress call.

As the airplane descended toward the CFI's chosen forced landing site, the CFI executed a 180-degree turn with full flaps and landing gear extended, and he entered a full slip. During this time, the engine continued to develop a minimum (idle) level of power. The airplane touched down on upsloping terrain and impacted a rocky berm.

During an interview with the Safety Board investigator, the CFI opined that the throttle control had become dysfunctional, since it moved too freely, and it was obviously "disconnected" from the engine's carburetor. The student reported that they had moved the throttle control through its full range of operation (from its full forward to its full aft stops) without obtaining any noticeable change in the engine's power (rpm).

The Safety Board investigator's subsequent examination of the accident airplane revealed that the throttle control cable was, in fact, disconnected at its carburetor rod end attachment fitting. The cable's threaded bolt end indicated no evidence of screw thread deformation, and there was no evidence of thread deformation in the carburetor's rod end attachment fitting. Investigators noted that the jam nuts on the control cable, which are used to secure the cable to the rod end, were tight against each other, but were not positioned close enough to the rod end to secure the cable to the carburetor. Additional assembly discrepancies were noted with the throttle cable's attachment to the carburetor. (See the Wreckage Examination report in the docket for additional details and photographs.)

Investigators noted chordwise scratches on both propeller blades. No evidence of pre-impact oil leakage was noted in the engine compartment. All of the flight control surfaces were found with the airplane. Neither pilot reported having experienced any preimpact flight control malfunction.

Following examination of the accident airplane, investigators examined the flight school operator's fleet of airplanes located in Santa Monica. According to the operator's representative, the flight school employed two fulltime mechanics. One mechanic, who was employed as the maintenance director, held an FAA airframe and power plant certificate with inspection authorization. The maintenance director had responsibility for oversight of the FAA certified airframe and power plant mechanic who had performed a majority of the maintenance on the flight school's fleet of airplanes, and who had performed the last two accident airplane inspections.

The operator maintained its airplanes on a program of annual and 100-hour inspections. The accident airplane's last 100-hour inspection had been performed on July 3, 2008, 6 days prior to the accident.

The Cessna Aircraft Company publishes a Service Manual that delineates the procedures to be followed in maintaining the accident model of airplane. In pertinent part, the manual specifically addresses how to attach and secure the throttle control cable to the carburetor. It also provides instructions regarding how to verify that the attachment is correctly accomplished.

The operator's representative reported to the Safety Board investigator that the flight school utilized a record keeping system for pilots to log abnormal airplane conditions/discrepancies in the airplane's dispatch book and/or in the flight school's computerized tracking program. Discrepancies (squawks) logged in the computerized system were visible by all company management.

At the time of the Safety Board investigator's fleet examination of the six Santa Monica-based airplanes, no logged discrepancies were found in the dispatch books, or in the computer system for any of the airplanes. A CFI-employee, who was not associated with the accident, reported to the Safety Board investigator that he worked for the operator on a full time basis. The CFI stated that he routinely does not write down squawks in the company's records. Rather, as the occasion necessitates and avails itself, he verbally informs staff of problems with the airplanes. Flight school management responded to this employee's disclosure by indicating to the Safety Board investigator that it was unaware of the lack of adherence to its policy to make a written record of squawks.

During the Safety Board investigator's examination of the Santa Monica-based fleet of seven airplanes, maintenance-related anomalies were found with each airplane. For example, one airplane exhibited jam nuts on the throttle control cable that were not adjacent to each other. The Safety Board investigator turned the cockpit throttle control knob counterclockwise through 20 360-degree rotations, and the threaded bolt of the control cable correspondingly turned counterclockwise and completely disconnected itself from the rod end housing at the carburetor. (See the Fleet Examination report in the docket for additional details and other observed discrepancies including restricted movement of the cockpit fuel selector and mixture controls.)

The operator participated in the Safety Board's accident investigation. As a result of this participation and the investigator-initiated fleet examination, the operator took immediate action to address the noted airworthiness-related maintenance abnormalities. The operator reinforced employee reporting squawk procedures, and enhanced management's oversight of both the flight and maintenance departments throughout its nationwide base of 50 airplanes and 300 employees.