Any time repairs or other work is performed on an aircraft, it’s a good idea to conduct a post-maintenance test flight to ensure everything is working as it should. There’s even a regulation, FAR 91.407, covering such flights and the “operational check of the maintenance performed or alteration made.” In many ways, someone conducting such a flight is a test pilot, determining whether the work performed was completed properly and the aircraft performs as intended.
During such flights, we generally plan to conduct a functional check of any and all systems potentially affected by the work performed and return. This, of course, presumes we don’t find a problem with the work performed. If we do find a problem during our post-maintenance check flight, an obvious response is to get the aircraft back on the ground expeditiously and resolve the issue. Depending on the problem, we may or may not be in a hurry: To us, an engine oil leak would mean hurry up and land, while a flight-control system issue might encourage us to take things easier and handle the aircraft gently.
In any event, we’re likely to be a bit busier when trying to return and land safely than might otherwise be the case. In a potential worst-case scenario, we’re flying an aircraft with a leaking hydraulic system operating various primary and secondary controls: If the leak continues, it’s a matter of time before we no longer can deploy landing gear, flaps or speed brakes, or control the airplane.
That’s apparently what happened when a former military jet trainer crashed short of a Florida runway two years ago: It’s likely hydraulic leaks resulted in secondary control system failures, leading to an over-enthusiastic attempt to land.
On February 2, 2011, at about 1729 Eastern time, a Potez-Air Fouga CM 170 Magister was substantially damaged when it impacted terrain during a traffic pattern approach to landing at the Kissimmee (Fla.) Gateway Airport (ISM). The commercial pilot/owner and the commercial pilot/mechanic were fatally injured. Visual conditions prevailed. The flight was the first after maintenance to repair a number of hydraulic leaks.
Radar data indicate the airplane flew a right downwind leg, about one nm northwest of the runway, and at about 1100 feet msl and 210 knots groundspeed. Approaching the runway’s extended centerline, the airplane was at about 1000 feet msl at 212 knots groundspeed. It flew down the runway, arriving at the mid-field break position at about 700 feet msl and 216 knots groundspeed. The airplane then commenced a left break, climbing to 900 feet msl after about 90 degrees of turn. By about 180 degrees of turn, and almost abeam the runway threshold, the airplane was again at 700 feet msl, at 215 knots.
A plot of the radar track, together with the impact location, indicate that from the overhead position, the airplane made a half-circle turn to the abeam position, then eased out of the turn briefly to a straight course that angled toward the runway. The airplane then entered a steeply banked turn and descended to arrive at the impact location.
According to a flight instructor waiting to take off, he saw the airplane fly overhead to a left break. As the airplane turned toward the final approach course, it pitched up and its angle of bank increased. The airplane overshot the final approach course, and was banked approximately 90 degrees when it lost altitude and impacted the ground short of the runway.
Another witness saw the airplane approach then make a “steep” descent. It appeared the pilot attempted to “gain control,” but the airplane made a “second drop” before the witness lost sight of it.
Both pilots were ejected from the airplane upon impact; neither cockpit contained personal items indicating which pilot was seated where. However, both pilots held commercial certificates with multi-engine land ratings plus FAA authorization to serve as PIC aboard the CM-170.
The initial ground impact scar was located in an open field about 1750 feet and 060 degrees from the Runway 24 threshold. Ground scars continued for about 175 feet, along a heading of 225 degrees, to the main wreckage. Crush damage to the left wingtip tank was consistent with ground impact in a 40-to-45-degree, left-wing-down bank; an attitude indicator from the rear cockpit was jammed in the 45-degree, left-wing-down, five-degree nose-down position.
The landing gear lever in both cockpits was in the down position, and damage to both separated main landing gear and the attached nose landing gear was consistent with their being extended at the time of impact. The emergency landing gear push-button selectors were in the “normal” position.
The airbrakes were operated by a throttle-mounted thumb toggle switch. The emergency airbrake selector was found in the “out” position; the hydraulic hand pump handle was not extended. The left airbrakes were found in the stowed position; the right airbrakes were found extended about an inch. Both engines exhibited rotation at impact.
According to the NTSB and the aircraft’s crew manual, the hydraulic system operates the landing gear, brakes, wing flaps, airbrakes and aileron servo-control. Emergency operation is accomplished by a hand pump in the front cockpit, which operates only the landing gear and airbrakes. Manual aileron control is accomplished by applying “right and left ailerons to engage the locking plungers of the servo-actuators.”
Configuration of the aircraft’s secondary flight and emergency system controls were consistent with the pilots sustaining a hydraulic system failure while configuring the airplane for landing.
The NTSB determined the probable cause(s) of this accident to include: “The pilot/mechanic’s improper decision to continue a tight-turning landing pattern after a loss of hydraulic pressure, and his subsequent failure to maintain adequate airspeed during that pattern, which resulted in an accelerated maneuver stall. Contributing to the accident was a loss of hydraulic pressure after the extension of the landing gear.”
Presuming the NTSB is correct about hydraulic system failure, a prudent response would have been to abandon the overhead landing approach, fully configure the airplane for the failure—including aileron application for manual reversion—and return for a landing. Instead, the pilots apparently tried to regain aileron control with steep banking during the break, leading to an accelerated stall at low altitude.