Date: 201601
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: PA-31 Navajo/Chieftan/Mojave/T1040
Operator: Air Taxi
Operating under: Part 135
Mission: Cargo / Freight / Delivery
Flight phase: Landing
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Air Taxi
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Commercial
Human factors: Other / Unknown
Second reporter function: Pilot Not Flying; Captain
Anomaly: Ground Excursion Runway; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
Result: General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Ambiguous

Narrative: On the descent the pilot flying prepared the aircraft for approach and landing.  Approach advised the crew to expect the visual for runway 03; after which the crew briefed the approach and landing. The winds were 340 @ 11 kts. A normal approach to landing was made in which the pilot flying landed the aircraft on runway 03 slightly right of centerline. The mains touched softly and the nose was slowly lowered down to the runway. The pilot flying then pushed the prop levers full forward for aerodynamic braking. While maintaining centerline for a brief period the pilot flying stated to the pilot monitoring 'it's gusty'. Meanwhile the pilot flying ensured the aircraft's ailerons were in the correct wind position. As the aircraft slowed; the pilot flying began softly applying both brakes. Initially the aircraft started slowly turning to the left. The pilot flying then applied slight right rudder. After applying slight right rudder with no change in direction the pilot flying pressed harder on the brakes and pushed harder with his right leg to counter the left turn with right rudder. It seemed as if the right rudder/brake input was not correcting the left turn. The pilot flying then applied brakes with more force as the aircraft continued its turn with greater rate. At this point the pilot flying called out 'Rudder; Rudder; Rudder' in hopes that the pilot monitoring would be able to counter the left turn or brake; stopping the aircraft. It happened extremely fast and before the pilot flying knew it the aircraft was sliding sideways to a stop on the left side of runway 03. The pilot flying's best guess as to the speed at which the sliding turn occurred was 30-50kts while rapidly decelerating.The pilot flying took a second to evaluate the current state of the aircraft and crew at which point both crewmembers immediately began securing the aircraft and shutting down the engines. The pilot monitoring handled all radio communications. Tower asked if the crew needed emergency vehicles and the crew declined; as there was no immediate threat or injuries. Tower informed the crew that they were shutting down runway 03. The pilot monitoring informed tower that they would call their maintenance team to have them towed to their ramp. An airport operations vehicle greeted the crew at their aircraft. The airport operations representative took the crews names; addresses; and phone numbers. An inspection was made of the aircraft; the runway; and the runway environment. The pilot in command; the second in command; and the airport operations representative performed the inspections. No damage was present to the runway; aircraft; or surrounding structures. Maintenance arrived and inspected the aircraft. Maintenance found no damage of immediate concern and cleared the plane to be towed.


Second narrative: The approach was normal in all respects -- aircraft configured properly (gear and flaps); approach speeds correct; the runway alignment was good; and checklists were accomplished appropriately. The wind was within the Chieftain's performance limits (demonstrated 20 knot direct crosswind component). Just before touchdown there were some wind gusts that required the pilot flying to address which he did appropriately. The touchdown was very smooth and very close to the centerline. After touchdown; including the nose tire; the pilot flying advanced the prop controls to the full forward/fine pitch setting and applied aerodynamic braking with up elevator as prescribed by standard operating procedures. The airplane began to slow down from its touchdown speed. The pilot monitoring did not have his hands on the control yoke or his feet on the rudder pedals during the approach; landing and runway departure sequence.Shortly after the touchdown and landing rollout began; the airplane started turning left and this left turn continued until the airplane was skidding sideways off the left side of the runway. After the departure sequence started; the pilot flying said 'Rudder; Rudder; Rudder' but the pilot monitoring did not have time to react before the skid had advanced to the point that directional control was still possible. The right main and nose tires slid off the shoulder of the runway into the dirt while the left main tire remained on the runway shoulder. The pilot monitoring estimates the airplane's heading slewed to the left by more than 90 degrees but less than 180 degrees from the Runway 3 heading -- say about 135 degrees. The pilot monitoring estimates that the airplane was moving at about 40 knots at the time the departure started and that the entire departure sequence lasted about 3 - 5 seconds.There were skid marks from each of the three tires. The skid mark for the left main tire started earlier and was narrower and darker than the skid marks from the right main and nose tires. The right main and nose tire skid marks correspond to the time when the aircraft was moving laterally/skidding. There were no personal injuries. The landing gear did not collapse. None of the tires were flat. There was no prop strike. The aircraft did not strike any runway lights or cause any other damage to the runway. There was no debris left on the runway as a result of the excursion. There was no damage to any of the cargo on board.The PIC; who was handling all radio communications; told the tower that the plane would have to be shut down where it was and then towed off the runway. The PIC told the tower that he would call the company and ask for maintenance to come out to tow the airplane. The tower closed Runway 3/21 temporarily. Tower asked if it should dispatch any equipment. The PIC declined that offer as it wasn't necessary. An airport representative drove to the plane within a few minutes and a few minutes later escorted maintenance personnel to the plane. The maintenance personnel briefly inspected the airplane to determine that it could be safely towed off the runway and then towed it to the maintenance hangar without any further issues. There is insufficient information at this point as to why this event occurred so I have no suggestions at this time as to how to avoid any recurrence.


Synopsis: A PA31 flight crew reported a loss of control during landing with the First Officer flying. The landing had been normal up until the brakes were applied; then the aircraft began a slow turn to the left rapidly increasing to a full skidding rotation to the left with a runway excursion.