Accident Lockheed SP-2H Neptune N4692A,

Date:	Sunday 15 June 2014
Time:	20:44
Type:	Lockheed SP-2H Neptune
Owner/operator:	Minden Air Corporation
Registration:	N4692A
MSN:	726-7247
Year of manufacture:	1961
Total airframe hrs:	10484 hours
Engine model:	Wright R-3350-32WA Cyclone
Fatalities:	Fatalities: 0 / Occupants: 2
Aircraft damage:	Substantial, written off
Category:	Accident
Location:	Fresno Yosemite International Airport, CA (FAT) - United States of America
Phase:	Landing
Nature:	Fire fighting
Departure airport:	Porterville Airport, CA (PTV/KPTV)
Destination airport:	Porterville Airport, CA (PTV/KPTV)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
A Lockheed SP-2H, N4692A, was substantially damaged when the nose wheel landing gear collapsed during landing roll at the
Fresno Yosemite International Airport (FAT), Fresno, California. The airplane was registered to Minden Air Corporation and operated as Tanker 48 by the United States Department of Agriculture (USDA), Forestry Service.
The captain reported that following an uneventful aerial drop, the flight was returning to Porterville. During the descent check, he noticed that the hydraulic pressure indicated 0 and that the first officer subsequently verified that the sight gauge for the main hydraulic fluid reservoir was empty. The first officer opened the jet engine doors successfully as the captain selected gear down with no response. The captain notified base personnel at Porterville of the situation, and informed them that they would be orbiting to the east of the airport to troubleshoot. The captain and first officer performed the emergency checklist, and verified that the nose wheel landing gear was extended. The captain stated that the first officer then installed the pin in the nose wheel landing gear as part of the emergency checklist.
The flight diverted to Fresno due to a longer runway and emergency resources as both pilots briefed the no-flap landing procedure, airspeeds, and approach profile. As the flight continued toward Fresno, the flight crew informed Fresno Approach Control of the hydraulic system failure, and continued to perform the emergency gear extension checklist. The first officer extended the main landing gear using the emergency gear release, which resulted in three down and locked landing gear indications in the cockpit. As the flight neared Fresno, the first officer added 2 gallons of hydraulic fluid to the main hydraulic reservoir while the captain attempted to extend the flaps unsuccessfully. Subsequently, the flight landed normally on runway 26R.
During the landing roll, the nose wheel landing gear collapsed, and the airplane came to rest nose low.
The first officer reported that following completion of the emergency nose gear extension checklist, he physically inserted the nose gear pin in place prior to the landing at Fresno.
Examination of the airplane by representatives from the Forest Service revealed that the forward portion of the fuselage was structurally damaged. The airplane was recovered to a secure location for further examination.

PROBABLE CAUSE: "The collapse of the nosewheel landing gear due to the disengagement of the nosewheel landing gear pin. Contributing to the accident was the failure of the main hydraulic system due to overpressurization for reasons that could not be determined during postaccident examination of the airplane. "

Accident investigation: