Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 42; Flight Crew Total 2507; Flight Crew Type 146
Workload; Situational Awareness; Confusion; Troubleshooting
Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Chart Or Publication; Manuals; Procedure; Aircraft
The aircraft was being inspected by a Cessna mechanic due to veering left when the brakes were applied on wet pavement. Two crews had experienced this on two separate flights. I was on one of those previous flights into ZZZ. Our Lead Pilot also performed a high speed taxi the previous day. I was told to come out to the hangar to escort a Cessna Citation mechanic so that he could inspect the brakes. The Mechanic did several checks initially and found no issues. He informed me that he did not have all the tools needed to do all the inspections he needed to perform. The main equipment that he told me he needed was a pressure tester. He initially told me he thought the issue was related to a brake master cylinder or the metering valve. It was my understanding that the aircraft utilized cables from the toe brake pedals and actuated hydraulically by a brake metering valve. I saw that the Mechanic was in the process of reviewing the schematics. After looking at the schematics; he did confirm that the pilot and co-pilot brakes are controlled mechanically through cables from the toe brake pedals and actuated hydraulically by a brake metering valve. He showed me the schematics as well. Because he did not have a pressure tester; he said it would help him find the issue if we did a high speed taxi. He then talked to our Lead Pilot over the phone; and I was asked to perform a high speed taxi with the Mechanic. I was hesitant to do a high speed taxi because I've never done one in that jet or any jet. I also had a concern that the plane would veer to the left again as well. I called my Chief Pilot to inform him of the situation. I informed him that I had never done a high speed taxi and would feel more comfortable with another pilot with experience performing a high speed taxi in a jet. He told me he had full faith in me but understood I was uncomfortable with it having never done it before. He told me he would talk to the Lead Pilot. I talked to one of the other First Officers; with experience doing this procedure; while waiting and asked if he felt comfortable doing a high speed taxi with me. He said he was. He then called our Chief Pilot and told him he was comfortable doing the high speed taxi with me. Our Chief Pilot then told us to do the high speed taxi together.The Mechanic told us he wanted the brakes tested from the right and left seat. I was unsure why he wanted to test from both sides at this point and asked him specifically if checking both sides by doing a high speed taxi was needed and would help him in determining the cause of the issue. He told me it would and would still like to do it. Once the other pilot arrived; we boarded the plane and taxied out. I was in the right seat; [the other First Officer] was in the left seat; and the Mechanic was in the back. [The other First Officer] started both engines; I called Ground and we were told to taxi out to XX. It was agreed that I would do the initial check from the right seat. I took the controls at the hold short line and taxied out onto the runway. [The other First Officer] told me he would call my speeds. I powered up and allowed the aircraft to accelerate. [He] called 40 and 50 knots. At 40 knots; I began to bring the power levers back to idle. I subsequently applied the brakes and came to a complete stop. I did not notice any pull to the left. The Mechanic wanted to see it done from [the other side] (left seat) at that point. [The other First Officer] took the controls. I made the callouts at 40 and 50 knots. [He] pulled the power levers to idle. We accelerated to 60 knots. [He] applied the brakes and then we taxied off the runway. There was no pull to the left. We both confirmed to each other and the Mechanic that we did not feel a pull or veering to the left. I asked [the other First Officer] if he wanted me to ask Ground to taxi back to the hangar. [He] looked back at the Mechanic and asked if we should return to the hangar. The Mechanic said that he wanted to see one more high speed taxi from the left seat. I called Ground and they told us to taxi down to XY to perform the final high speed taxi. [The other First Officer] then powered up; and I repeated the speed callouts the same as our previous one. There was no veering to the left again. [He] then taxied off onto the taxiway. I called Ground and they told us to proceed back to the hangar. We were on a taxiway just getting ready to make the turn onto the tarmac in front of the hangar; when we started to feel vibration. [The other First Officer] stopped the plane and shut down the left engine. The Mechanic opened the door and informed us the left tire was flat. [The First Officer] then shut down the right engine. The Mechanic stepped out and informed us it was flat as well. We notified Ground Control and called the FBO at that point.The ground crew arrived with the tug and informed us they did not have any dollies to use for the aircraft and did not believe they would be able to get any that day because it was [a holiday]. [The other First Officer] asked the Mechanic his thoughts on how best to get it back to the hangar. The Mechanic said the wheels themselves would have to be replaced and to go ahead and tow it back. [The other First Officer] and I talked it over and agreed to call our Chief Pilot and Director of Maintenance before proceeding any further. It was decided that we should not move it until we could acquire dollies for both sides. We were able to acquire them later that evening so the plane could be moved to the hangar. This problem arose from a chain of events. I specifically informed my Chief Pilot that I was not comfortable doing the high speed taxi. A more experienced pilot was brought out to help perform the procedure. The Mechanic was the one that requested multiple high speed taxis and advised us on how he wanted it conducted and how many times. The problem could have been avoided if the Company and Mechanic didn't insist on a third attempt to check for veering to the left. The Mechanic could have had access to the correct tools (pressure tester) the following day to check the problem correctly. That in turn would have prevented the tires from overheating.
The cause of the dual tire deflation was caused by the thermal relief plugs melting in the rims; due to high rim/brake temperature. I feel that we weren't properly trained on this at CAE. I also feel that this wouldn't have happened if the Cessna Mechanic had known the proper tolerances and not request 3 high speed taxi tests from us. We assumed that if the Mechanic was asking for certain tests; that he felt it was within the aircraft limitations.
Two First Officers and a Mechanic performed three high speed rejects to test a C525 brake system and during taxi back to the ramp; the wheel fuses melted flattening the tires. No training was given about hot brakes and cooling times.