Improper Brake Use To Blame, Says Cirrus
Bentley said Cirrus has studied the incidents extensively and determined there are no design or equipment faults at work, and for Cirrus this leaves only "operator error" as the cause. Unlike many aircraft pilots may be transitioning from, Cirruses have a free castering nosewheel and are steered only with differential braking, plus some positive or negative contribution from the rudder (dependant on relative wind). Bentley said some pilots may have a tendency to overuse the brakes to compensate for excessive power settings or may simply be riding the brakes. Last June, the company e-mailed all its customers (click here for a pdf version) with an owner service advisory that warned them not to overtax the brakes, which Cirrus also says are more than adequate for an airplane with the performance and weight of a Cirrus. Bentley said that after the first reported brake fire, Cirrus and the brake manufacturer, Parker Hannefin, intentionally overheated sets of brakes and cycled them 19,000 times without a failure. Bentley said the components must be subjected to "significant overheating" to cause a fire. Thanks to the multi-function display installed on most Cirruses, Bentley said they have hard data to show how the overheating occurs. The MFD records engine RPM and speed. If the speed drops and the engine RPM stays the same, the only place that energy can go, according to Cirrus, is into the brakes. "This isn't speculation. There's a lot of real information around," he said. In at least one case, it appears the plane was taxied with the parking brake on, says Cirrus.