N432CD

HISTORY OF FLIGHTOn June 15, 2022, about 1620 central daylight time, a Cirrus SR22, N432CD, was substantially damaged when it was involved in an accident in Gulf Shores, Alabama. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight.

The accident occurred at Gulf Shores International Airport/Jack Edwards Field (JKA), Gulf Shores, Alabama. The flight was destined for Destin Executive Airport (DTS), Destin, Florida.

On April 7, 2022, the pilot landed at JKA. He felt that “the brakes were a little soft,” so he asked a maintenance shop at the airport to look at them. The description of the work on the receipt that he received was “Trouble shoot brake problem - Bled brakes and ops check good.” When the pilot returned to pick up the airplane, he performed a preflight inspection and proceeded to taxi. He noticed that the airplane required more power than usual in order to taxi, and he felt that the brakes were “dragging.” As the pilot parked and shut down the airplane, the rudder/brake pedals “went to the floor.” Personnel from the maintenance facility examined the brakes and told the pilot that they would need to be rebuilt. The airplane was towed back to the maintenance facility, where the brake piston O-rings and the brake pads on both calipers were replaced.

The pilot subsequently operated the airplane on approximately 21 more flights, and on May 27, 2022, flew the airplane to JKA for an annual inspection by the maintenance facility that performed the brake rebuild. During the annual inspection, maintenance personnel once again replaced the brake pads on both calipers and bled the brake system, stating in the maintenance log entry, “Operational check good” and “No further defects noted.”

On the day of the accident, the pilot returned to the maintenance shop to pick up the airplane. Following a preflight inspection, he taxied the airplane to the runway for takeoff. The pilot reported that the airplane felt “a little sluggish” taxiing onto the runway, and that after applying takeoff power, the airplane was not accelerating normally. The pilot aborted the takeoff and taxied the airplane off the runway.

The pilot then called the maintenance shop, and they asked him to try taxiing the airplane slowly back to the facility. When he attempted to move the airplane forward, he once again lost all braking effectiveness. He immediately shut off the magnetos and the airplane rolled to a stop just off the corner of the taxiway.

The pilot saw smoke coming from under the airplane, exited the airplane to check on the smoke, and told his passenger to exit also. He observed a fire on the right main landing gear and used the fire extinguisher on board the airplane to put out the fire. He realized that the left main landing gear had caught fire as well. He then reached back into the airplane and grabbed two water bottles that he had in the airplane and used them to try to extinguish the fire on the left main landing gear, but was unsuccessful. He then called 911 and moved away from the airplane. AIRCRAFT INFORMATIONThe airplane used a free-castering nose wheel and relied on aerodynamic forces and differential braking for directional control while taxiing. AIRPORT INFORMATIONThe airplane used a free-castering nose wheel and relied on aerodynamic forces and differential braking for directional control while taxiing. WRECKAGE AND IMPACT INFORMATIONPostaccident examination of the airplane by the NTSB revealed that the left side of the fuselage and the left wing had been substantially damaged by the fire. The hydraulic fluid reservoir contained brake fluid. The parking brake was functional and was not engaged. The hydraulic plumbing in the cockpit did not display any evidence of leakage, and all four master cylinders (one on each rudder pedal) and their associated plungers were intact.

The right main landing gear wheel could be rotated by hand, and the brake caliper displayed surface discoloration on the top 1/3rd of the caliper. The brake caliper and brake pads were thermally damaged, and the brake line fitting could be moved by hand.

The left main landing gear wheel was separated from the rest of the landing gear assembly as a result of thermal damage. The tire was fire-damaged along with the brake caliper, which displayed cracking. One of the two pistons was partially extended. The caliper was missing its fittings, and the brake pads were not present. The brake line swage fitting was present, but required very little torque to remove. FLIGHT RECORDERSThe airplane was not equipped with a flight data recorder, nor was it required to be. It was, however, equipped with an Avidyne Entegra avionics suite, which was capable of recording event data, flight data, engine monitoring data, and performance data.

According to the recorded data, the airplane powered up at approximately 1559:00 and began taxiing at approximately 1609:00.

At 1611:36, the airplane had reached taxiway A and followed taxiway A due east to taxiway A5.

At 1611:52 it took about 1,250 rpm to get up to 15 kts after turning onto the taxiway. Once the airplane was rolling down the taxiway, it maintained 15 kts for 30 seconds with only about 1,040 rpm.

At 1612:22 engine power had increased to 1,260 rpm and the airplane was moving at approximately 20 kts.

At 1612:58, power was reduced to 1,100 rpm and the ground speed slowed down gradually over a 60-second period to around 12 kts, which was slower than the first 15-kt reference point.

At 1613:52, power increased to 1,450 rpm and the ground speed increased to 18 kts but no higher, indicating that brakes might have been applied. Power was then reduced to 1,300 rpm, but it gradually increased again up to 1,500 rpm, even as the ground speed decayed. Then as the airplane made the 90-degree turn into the hold short position while also decelerating, power decreased to 1,200 rpm going into the turn, increased to 1,400 rpm through the turn, and then decreased to idle range, with the airplane coming to a stop after the turn.

About 1617:44, the airplane lined up on runway 27. At approximately 1618:00, the airplane began to accelerate, reaching 62 kts airspeed before it began to decelerate.

At approximately 1618:52, the airplane exited the runway at taxiway A3. TESTS AND RESEARCHBrake System

The main wheels were equipped with hydraulically operated, single-disc type brakes. A parking brake mechanism held induced hydraulic pressure on the disc brakes for parking. The brake system consisted of a master cylinder for each rudder pedal, a hydraulic fluid reservoir, a parking brake valve, a single-disc brake assembly on each main landing gear wheel, and associated hydraulic plumbing. Braking pressure was initiated by depressing the top half of a rudder pedal (toe brake). The brakes were plumbed so that depressing either the pilot’s or copilot’s left or right toe brake would apply the respective (left or right) main wheel brake. The reservoir was serviced with MIL-H-5606 hydraulic fluid.

According to the airplane manufacturer, brake system malfunction or impending brake failure would be indicated by a gradual decrease in braking action after brake application, noisy or dragging brakes, soft or spongy pedals, excessive travel, and/or weak braking action. They advised that should any of these symptoms occur, immediate maintenance was required.

The airplane manufacturer also advised that proper braking practices were critical to avoid potential damage to the brakes and that the most common cause of brake damage and/or failure was the creation of excessive heat through improper braking practices. Pilots unaccustomed to free-castering nose wheel steering may be inclined to "ride" the brakes to maintain constant taxi speeds and use the brakes excessively for steering.

When taxiing, directional control was accomplished with rudder deflection and intermittent braking (toe taps) as necessary. The airplane manufacturer advised to only use as much power as necessary to achieve forward movement and deceleration and that taxi speed control using brakes without a reduction in power would result in increased brake temperatures.

Manufacturer guidance indicated that engine speed should not exceed 1,000 rpm for taxi operations on flat, smooth, hard surfaces. Power settings slightly above 1,000 rpm were permissible to start motion and for turf, soft surfaces, and on inclines. The manufacturer cautioned that, "riding the brakes" while taxiing is similar to driving a car with one foot on the brake and one foot on the gas. This causes a continuous buildup of energy that would otherwise be moving the airplane.

Examination of Brake Assemblies and Brake Discs

Examination of the brake assemblies and brake disks was conducted at Aircraft Wheel and Brake LLC (formerly Parker Hannifin's Aircraft Wheel & Brake Division), in Avon, Ohio.

Both brake housings exhibited evidence of extreme heat exposure. The paint was completely burned off and the brake housings appeared dark gray to chalky white in color. The identifying brake assembly name plates were no longer present.

Examination of the left brake assembly revealed that it had been serviced with metallic linings. Although no linings were present, it was determined that metallic linings were used because the back plates and the pressure plate had lining pins installed. Lining pins are only used with metallic brake linings.

The left brake housing displayed extreme cracking, and the section of the brake housing containing the anchor bolts was completely broken off. The backplates and pistons were still present in the left brake assembly. As noted during the wreckage examination, one of the pistons was partially extended.

The left brake disc exhibited an absence of paint and dark, non-metallic coloring consistent with exposure to extreme heat. The brake disc was made of steel alloy and was plastic-media blasted to clean it for bett...