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On July 15, 2006, about 1630 Pacific daylight time, a Lear 55, N554CL, had an in-flight fire on approach to Van Nuys, California. Clay Lacy Aviation was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 135. The airline transport pilot licensed captain, first officer, and three passengers were not injured; the airplane sustained substantial damage. The cross-country flight departed Las Vegas, Nevada, about 1546, with a planned destination of Van Nuys. Visual meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan had been filed.
The pilot stated that the airplane was on approach to landing. About 500-600 feet above ground level (agl), the emergency pressurization and right bleed air annunciator lights illuminated simultaneously. There was no change in the cabin pressurization, and the crew decided to continue and land. About 100-200 feet agl, the left bleed air light illuminated, and pressure went to emergency. The crew switched the cabin air off. They landed, taxied quickly to their parking area, and turned the left and right bleed air switches off prior to engine shutdown.
The flight line crew notified the flight crew that smoke was coming out of the ram air vent in the dorsal fin area. Both the flight and ground crew expedited off-loading of the passengers, and stood by with fire extinguishers. The smoke subsided. The pilot indicated that no smoke or smells entered the cabin or cockpit. He also pointed out that the air conditioner was blowing hot air and operation appeared to be intermittent; the passengers had complained about the high temperature in the cabin.
The operator reported that the pilot held an airline transport pilot certificate with ratings for airplane multiengine land. He held a commercial pilot certificate with ratings for single-engine land, glider, and instrument airplane. The pilot held a certified flight instructor (CFI) certificate with ratings for airplane single-engine land, multiengine land, glider, and instrument airplane.
The pilot had a first-class medical certificate issued on March 28, 2006. No limitations or waivers were listed.
The operator reported that the pilot had a total flight time of 3,798 hours with 395 hours in this make and model. The pilot logged 200 hours in the last 90 days, and 71 hours in the last 30 days. A biennial flight review was completed on April 16, 2006.
The operator reported that the copilot held an airline transport pilot certificate with ratings for airplane multiengine land. The copilot held a commercial pilot certificate with ratings for single-engine land and instrument airplane.
The copilot held a first-class medical certificate issued on January 23, 2006. No limitations or waivers were listed.
The operator reported that the copilot had a total flight time of 3,000 hours with 150 hours in this make and model. The copilot logged 170 hours in the last 90 days, and 71 hours in the last 30 days. A biennial flight review was completed on October 24, 2006.
The airplane was a Learjet 55, serial number 040. The operator reported that the airplane had a total airframe time of 10,343 hours at the time of the accident. The airplane was on a continuous airworthiness maintenance plan, and the last conditional inspection occurred on July 14, 2006.
The left engine was a Garrett TFE-731-2-2C, serial number P85184C. Total time recorded on the engine was 10,043 hours, and time since major overhaul was 3,468 hours.
The right engine was Garrett TFE-731-2-2C, serial number P85191. Total time recorded on the engine was 9,890 hours, and time since major overhaul was 2,458 hours.
COCKPIT VOICE RECORDER (CVR)
A Safety Board specialist prepared a summary report of information from the CVR. The report indicated that the copilot advised the captain about 25 minutes before landing that the cabin temperature gauge was pegged. Two minutes before landing, the copilot extended the landing gear, read the before landing checklist, and changed the air conditioner to fan. Shortly thereafter, the copilot made a comment about emergency pressurization; the pilot suggested that they make no changes right then. About 40 seconds before landing, the copilot made a comment about the bleed air, and the pilot commanded that cabin air be turned off.
Sixteen seconds after touchdown, the copilot suggested that they recycle a switch, but the pilot said not to. One minute and 50 seconds after touchdown, the pilot called for turning the air conditioning off. Fifteen seconds later, the crew shut the engines off. Ten seconds later, the pilot indicated that there was smoke in the cabin, and ordered the passengers to evacuate the airplane.
TESTS AND RESEARCH
The Safety Board investigator-in-charge (IIC) supervised examination of the airplane at Van Nuys, California, on July 19-20, 2006.
Visual Examination on Site
Examination of the cockpit revealed popped circuit breakers for the ECS (environmental control system) on the pilot's (left) side and the ECS on the copilot's (right) side, windshield heat, alcohol system, and right bleed air.
Investigators observed fire damage to the windshield heat shutoff valve, left and right mixing valve control boxes and associated wiring, landing light/taxi light/auxiliary hydraulic pump relay box, upper side of the flow control valve, and the windshield heat shutoff valve and wiring.
The steel braided low pressure air conditioning line burned from the compressor outlet to the aft cabin evaporator except for a 2-foot section in the middle of the line. This portion of the hose was the only section that did not have rubber hose wrapped around it.
Tests on Site
Maintenance personnel used a ground pressurization unit to apply 10 pounds per square inch (psi) air to the ground service port.
A slight air discharge from exhaust port was felt on the flow control valve. A larger air leak was detected from the cockpit air duct temperature sensor, which the Lear representative noted should not leak at all. Ten psi air pressure was applied, and no airflow was detected at the windshield heat duct outlets. Twenty-eight volt power was applied to the windshield heat shutoff valve, which opened the valve, and airflow was detected at the windshield heat duct outlets.
External visual examination revealed heat discoloration and wavy skin on the aft fuselage skin starting at station 512.39, frame 39, which extended aft to station 544.39, frame 41. Internal examination of the empennage in the tail cone access door revealed that frames 39, 39a, and 41 were scorched and sooty.
Windshield Flow Control Valve
The IIC supervised examination of the windshield flow control valve, Whitaker, part number 320335-3, serial number 507. It passed all parameters on a test bench with no anomalies noted.
The IIC supervised examination of the windshield anti-ice shutoff valve, Vickers, manufactured second quarter 1992 (2Q92), part number 6600201-1, serial number 2135. It passed all parameters on a test bench with no anomalies noted.
Windshield Anti-ice Modulating Valve
The windshield heat modulating valve, part number 32-2867-003, serial number 05860077, was functionally tested at three separate facilities under supervision of either the IIC or FAA personnel. With the actuator correctly grounded, actuator operation was normal. No pre-existing condition, either mechanically or electrically, was identified with the heat modulating valve that would have interfered with normal operation.
August 28, 2008 Testing
A visual examination revealed soot on the external surfaces of the main valve body housing. As received, the valve was not fully closed. There was evidence of blow-by on the outflow flange of the valve.
With 80 psig pressure supplied to the inlet of the air valve, there was leakage between the actuator motor and the main valve housing, and between the inlet flange housing and the main valve housing. The internal leakage was 0.1234 lb/min, which exceeded the 0.05 lb/min test limit. With the valve direction reversed, internal leakage exceeded the 0.05 lb/min test limit (The actual value of the leakage in the reversed configuration was not recorded).
After test personnel functionally tested the air valve, they performed a limited teardown of the air valve. The actuator motor was first separated from the main valve housing, and the actuator motor cover was removed from the assembly. There was a witness mark on the heat shrink covering the actuator wires, and on the corresponding inner surface of the actuator motor cover.
Once the actuator motor was disassembled from the main valve housing, the butterfly valve assembly was free to rotate. Two of four bolts attaching the inlet housing to the main valve housing were loose. The packing between the inlet flange housing and the main valve housing was dry, pitted, and had flat spots.
Lear engineers felt that more damage would be expected at the valve if bleed air had been the initiator. With the substantial damage to the wiring harnesses around and near the valve in question, they felt that it was equally plausible that the fire initiator could have been electrical in origin.