What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
On 10/7/2015 the pilot of N505ZW, a Cub-crafter (an elsa/Cub) was landing @ lzu/rwy 25. The weather was exceptional, (ATIS p METAR klzu 072045Z 00000KT 10SM clr 27/12 A3007) with a no wind condition.
The pilot stated as the aircraft touched down, with the aircraft aligned with the runway, the left main gear touched down first in a normal/firm manner. The pilot then stated that he thought the left tire deflated because the left side of the aircraft fell limp and then the aircraft started to veer to the left. The aircraft came to a stop after the aircraft departed from the center of the runway with the left wing tip contacting the grass/soil area to the left of the runway.
When the aircraft was initially looked at (it was moved into the owner's hangar #5 on the eaa hanger row), it seems that the left main collapsed and folded under the aircraft, possibly due to a pilot induced sideload.
The initial mechcanical evaluation that was made indicated that the wheel/bearing assembly may have failed, which lead to the failure of the cabane vee assembly and the shock cover asseembly which allowed the gear to collapse and caused the aircraft to veer off the runway. This initial mechanical evaluation leads to an outcome that seems to be a mechanical issue verses a pilot induced error, but FAA waited for the results of the teardown of the wheel assembly to make this determination.
The inspectors asked the operator^/owner/^pilot to let them know when the tear-down of the left wheel assembly was to be conducted so they can determine what happened.
Instead, the operator^/owner/^pilot called the FAA after the teardown was completed. An a/w inspector went and looked at the replaced parts.
The first thing the a/w inspector noticed was that there was no main gear axle nut cotter pin. This could have caused the axle nut/bearing assembly/outter wheel half to come loose after multiple landings. This could have lead to the failure of the outter half of the wheel assembly.
As the FAA filed it
ON 10/7/2015 THE PILOT OF N505ZW, A CUB-CRAFTER (AN ELSA/CUB) WAS LANDING @ LZU/RWY 25. THE WEATHER WAS EXCEPTIONAL, (ATIS P METAR KLZU 072045Z 00000KT 10SM CLR 27/12 A3007) WITH A NO WIND CONDITION.
THE PILOT STATED AS THE AIRCRAFT TOUCHED DOWN, WITH THE AIRCRAFT ALIGNED WITH THE RUNWAY, THE LEFT MAIN GEAR TOUCHED DOWN FIRST IN A NORMAL/FIRM MANNER. THE PILOT THEN STATED THAT HE THOUGHT THE LEFT TIRE DEFLATED BECAUSE THE LEFT SIDE OF THE AIRCRAFT FELL LIMP AND THEN THE AIRCRAFT STARTED TO VEER TO THE LEFT. THE AIRCRAFT CAME TO A STOP AFTER THE AIRCRAFT DEPARTED FROM THE CENTER OF THE RUNWAY WITH THE LEFT WING TIP CONTACTING THE GRASS/SOIL AREA TO THE LEFT OF THE RUNWAY.
WHEN THE AIRCRAFT WAS INITIALLY LOOKED AT (IT WAS MOVED INTO THE OWNER'S HANGAR #5 ON THE EAA HANGER ROW), IT SEEMS THAT THE LEFT MAIN COLLAPSED AND FOLDED UNDER THE AIRCRAFT, POSSIBLY DUE TO A PILOT INDUCED SIDELOAD.
THE INITIAL MECHCANICAL EVALUATION THAT WAS MADE INDICATED THAT THE WHEEL/BEARING ASSEMBLY MAY HAVE FAILED, WHICH LEAD TO THE FAILURE OF THE CABANE VEE ASSEMBLY AND THE SHOCK COVER ASSEEMBLY WHICH ALLOWED THE GEAR TO COLLAPSE AND CAUSED THE AIRCRAFT TO VEER OFF THE RUNWAY. THIS INITIAL MECHANICAL EVALUATION LEADS TO AN OUTCOME THAT SEEMS TO BE A MECHANICAL ISSUE VERSES A PILOT INDUCED ERROR, BUT FAA WAITED FOR THE RESULTS OF THE TEARDOWN OF THE WHEEL ASSEMBLY TO MAKE THIS DETERMINATION.
THE INSPECTORS ASKED THE OPERATOR^/OWNER/^PILOT TO LET THEM KNOW WHEN THE TEAR-DOWN OF THE LEFT WHEEL ASSEMBLY WAS TO BE CONDUCTED SO THEY CAN DETERMINE WHAT HAPPENED.
INSTEAD, THE OPERATOR^/OWNER/^PILOT CALLED THE FAA AFTER THE TEARDOWN WAS COMPLETED. AN A/W INSPECTOR WENT AND LOOKED AT THE REPLACED PARTS.
THE FIRST THING THE A/W INSPECTOR NOTICED WAS THAT THERE WAS NO MAIN GEAR AXLE NUT COTTER PIN. THIS COULD HAVE CAUSED THE AXLE NUT/BEARING ASSEMBLY/OUTTER WHEEL HALF TO COME LOOSE AFTER MULTIPLE LANDINGS. THIS COULD HAVE LEAD TO THE FAILURE OF THE OUTTER HALF OF THE WHEEL ASSEMBLY.