HISTORY OF FLIGHT Use your browsers 'back' function to return to synopsisReturn to Query Page
On December 17, 1998, at 0856 Pacific standard time, a Learjet 55B twin-turbojet airplane, N554CL, made a gear-up landing at Los Angeles, California, after experiencing progressive loss of all electrical systems while en route. The aircraft sustained substantial damage; however, neither the captain, first officer, nor the five passengers onboard were injured. The aircraft was registered to IMP Inc., Van Nuys, California, and was being operated as an on-demand air taxi under 14 Code of Federal Regulations Part 135 by Clay Lacy Aviation, Van Nuys, when the accident occurred. The flight originated from San Diego, California, about 0830, and was destined for Los Angeles, California. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed.
According to the captain's written statement, the flight crew was told by clearance delivery to expect a takeoff time of 0835, so the captain "decided to start the right engine and taxi out while waiting for departure clearance." The flight crew was then given a takeoff clearance prior to their expected time, and "started the left engine while taxiing to the runway and did the take-off checklist." The flight crew was told to change to the southern California (SoCal) departure controller. After the flight crew changed frequencies, the departure controllers experienced difficulty hearing the accident flight's radio transmissions. The flight crew could hear the controller; however, the controller could not hear them. The SoCal controller told the flight crew to contact Los Angeles (LAX) approach control.
The captain stated that once they crossed Long Beach Airport (approximately 15 nautical miles from LAX), "my instruments failed and we could not communicate with approach." He added that since the sky was clear and visibility unrestricted, he elected to extend the flaps and lower the landing gear. The captain remembered selecting 20 degrees of flaps and attempting to lower the landing gear; however, he could not determine whether the landing gear were extended. The captain elected "to make a low pass with the intent to land if [the landing gear] were down. Since it was obvious that [the landing gear] were not down, [he] made a go-around." The captain then "pushed the blow down lever thinking that this would extend [the landing gear]."
The captain stated that he entered final approach with the expectation of landing with the landing gear extended; however, he was prepared for a gear retracted landing if they were not. The pilot landed the airplane "as smoothly as [he] could." He added that the airplane continued straight down the runway until he lost rudder control, at which time the airplane turned sideways and slid onto the high speed turnoff.
The captain stated that he had pulled the firewall shutoff handles just prior to landing; however, "they were inoperative because of the electrical failure." He added that the first officer opened the door and evacuated the passengers. The captain attempted to shutdown the engines "using the normal shut down procedure; however, he was unable to do so because the linkage had been damaged due to the landing." The crash/fire and rescue personnel stopped the engines by spraying fire retardant foam into the engine intakes. The captain added in his statement that they did not utilize the emergency landing gear free fall system to extend the landing gear.
The airplane's cockpit voice recorder was sent to and transcribed by the NTSB recorder laboratory in Washington, D.C. According to the recorder transcripts the flight crew was taxiing out to the runway and running through the takeoff checklist, when the co-pilot called for the engine instrument check. The captain indicated that they could not "do that yet until we...start the other engine." The first officer replied "we'll stand by engine and electrical," and the captain stated at 0826:26, to "just standby everything," to which the first officer responded in the affirmative. At 0826:43, the first officer contacted the departure airport tower and indicated that they were "ready to go, uh upon our clearance time." At 0826:50, the tower cleared N554CL to taxi into position and hold for a 30-second to 1-minute delay on the runway. At 0827:11, the captain called for the runway items on the takeoff checklist. At 0827:19, a sound similar to an engine ignition could be heard on the recording. At 0827:30, the first officer responded, "okay before takeoff checklist complete." At 0828:09, N554CL was cleared for takeoff.
At 0832:58, the captain asked if they had the navigation lights on, to which the first officer responded in the negative. The captain then replied, "I can't see any of these things. I think they must be." The first officer replied that the beacon and the navigation lights were not on. At 0833:25, the captain again stated that, "there's some lights on because this is dim. I can't see any of those." At 0833:38, the captain stated, "something isn't set right," to which the first officer responded, "I've got all my lights off on my side." At this point in the recording, the captain alerted the first officer that the altitude was increasing and that they were beginning to join their cleared course. At 0834:45, the first officer reported "I'll do the after takeoff checklist if that's okay," to which the captain responds in the affirmative. At 0834:51, the captain stated, "there's still something wrong with that light system." At 0835:03, the first officer reported that the after takeoff checklist was complete. Three seconds later, he reported that the climb checklist was complete. Four seconds after that, he reported that the descent checklist was complete.
At 0835:13, the recorder picked up a sound similar to an autopilot/yaw damper disengage tone. Two seconds later, the captain reported that the "autopilot isn't working." At 0835:55, the first officer attempted to get weather information for the destination airport. During this attempt, the recorded weather message became faint and unintelligible. During the first officer's attempt to retrieve weather information, the air traffic controller instructed N554CL to contact approach control on a different frequency. Review of the recording revealed that the flight crew attempted to contact approach control four times. After the fourth attempt, SoCal approach indicated that "whoever just called was broken and unreadable," and requested that whoever called to IDENT. The flight crew continued to try and contact the approach controller and at 0838:54, the controller indicated that N554CL's "radio is completely unreadable. I'm getting nothing but scratches and noise." The controller also informed the flight crew that he was not receiving any transponder signal from N554CL. Between 0839:01 and 0844:57, the flight crew attempted to contact approach control using different radios and different frequencies to no avail. At 0846:41, the captain told the first officer to check his circuit breakers. The first officer responded that all the circuit breakers were in. At 0847:24, the captain instructed the first officer to "see about the emergency and all that kind of stuff." At 0847:39, the captain again stated that he thought that the navigation lights were on "because it's too...these...are very dim." However, the first officer replied that they were "definitely off."
At 0848:38, N554CL was cleared for the instrument landing system (ILS) approach for runway 25L at the Los Angeles International Airport, and was told to switch to the tower frequency. After this point on the recorder, the flight crew could not hear any radio calls from air traffic control; however, they attempted switching radios and attempted contacting controllers until 43 seconds prior to landing gear up on the runway. It was apparent that the flight crew attempted to lower the landing gear; however, they were uncertain whether they were down and locked. Review of the recorder transcripts did not reveal which, if any, gear extension checklist was used. It also could not be determined if the flight crew ever completed the engine start checklist (which would include the online activation of the generators). Further review of the cockpit voice recorder transcripts revealed that the flight crew did not examine the electrical system switch positions nor did they perform the Dual Generator Failure checklist. The flight crew did not discuss any common denominator for the radio, autopilot, annunciator and indicator lights, and transponder malfunctions.
The captain held an airline transport pilot certificate for multiengine land airplanes, and commercial certificates for single engine land and multiengine sea airplanes. The captain was also type rated in the Learjet, along with the Boeing 727 and 747; DC-3, -6, -7, -8, and -10; and CV-240, -340, and -440 airplanes. The pilot was issued a flight instructor certificate; however, it had expired in 1973, and according to FAA records, it had not been renewed since. The captain was issued a first-class medical certificate on August 10, 1998, with a limitation that he "must wear corrective lenses." He was also issued a airframe and powerplant mechanic certificates in 1977. According to the captain's last medical application, he reported having had accumulated a total of 23,000 civilian flight hours. According to the Pilot/Operator Aircraft Accident Report that the captain submitted, he reported having had accumulated 25,000 total flight hours, of which 500 hours were in the same make and model as the accident airplane. The captain reported having flown a total of 70 hours within the preceding 90 days, of which 10 hours were flown in the same make and model as the accident airplane.
The co-pilot held an airline transport pilot certificate for multiengine land airplanes, and a commercial pilot certificate for single engine land airplanes. The co-pilot also held a flight instructor rating for single engine, multiengine, and instrument airplanes. He was issued a first-class medical certificate on November 23, 1998, with no waivers or limitations. According to his last medical application, the co-pilot reported having had accumulated a total of 2,100 flight hours. According to the Pilot/Operator Aircraft Accident Report, he had accumulated 2,231 total flight hours, of which 16 hours were in the same make and model as the accident airplane. The co-pilot reported that he flew 185 hours within the preceding 90 days, of which 9 hours were flown in the same make and model as the accident airplane.
Review of the Learjet 55 Pilot's Manual revealed that the aircraft's primary electrical power for aircraft and avionics systems requiring direct current (DC) is supplied by two engine driven, 30-volt (V), 400-ampre generators. Secondary DC electrical power is supplied by two 24-volt batteries. A voltage regulator is installed for each generator and they maintain a generator output of approximately 28 VDC throughout varying engine speeds and loads. During normal operation, the generators supply all aircraft DC power requirements by supplying a regulated 28 VDC output to their respective generator buses. The voltage on the generator buses is applied to the battery charging bus through 275-amp current limiters. Battery charge is maintained from the battery charging bus through the battery relays and battery buses. In the event that both generators either fail or are not on line, the batteries will supply electrical power the aircraft for a limited amount of time. The limited time will depend on the battery charge and condition at the time the generators go off line.
The starters and generators are controlled through the START L-GEN and START R-GEN switches on the center switch panel. Each switch has three positions: START, OFF, and GEN. During the engine start sequence, when the engine rpm reaches idle speed, the START-GEN switch should be set to GEN.
The GEN RESET switches are located on the center switch panel adjacent to the START-GEN switches. Each switch had two positions: RESET and NORM. The switches are spring loaded to the NORM position. Should an overvoltage relay open the affected generator field circuit, the flight crew can momentarily hold the applicable GEN RESET switch to RESET in order to reset the overvoltage relay, thereby closing the affected generator circuit.
There are two amber generator lights (L GEN and R GEN) located on the glareshield annunciator panel. The lights are controlled by the corresponding generator control circuits and will illuminate whenever the corresponding generator has failed or is off line. The light will also illuminate whenever the corresponding START-GEN switch is in either the START or OFF position and at least one battery switch is on.
The accident airplane also incorporated a Single Emergency Power System, which provides electrical power via another battery for the operation of flaps and landing gear if the EMER BAT switch is in the ON position.
The Learjet 55 Starting Engines checklist instructs flight crews to place the START-GEN switch to the GEN position once the engine is at idle. It then instructs the flight crews to check the DC VOLTS and AMPS for generator output.
The Before Taxi checklist and the Taxi and Before Takeoff checklists do not require an electrical system check. The Runway Lineup checklist requires the flight crew to check that the annunciator lights are out, "except STEER ON, GND IDLE, SPOILER ARMED (if applicable), and APR ARM (if applicable)."
The pilot's manual Emergency Procedures section informs flight crews to ensure that the GEN switches are on the GEN position and to activate the GEN RESET switches momentarily in the event that there is a "Dual Generator Failure (L and R GEN lights illuminated)."
According to the Learjet 55 Pilot's Manual, the landing gear is hydro-mechanically operated and incorporates an electrically operated selector valve. Electrical power for the selector valve circuit is 28 VDC supplied through a 2-amp GEAR circuit breaker. Alternate landing gear extension can be accomplished pneumatically in case of a hydraulic or electrical system failure. Pneumatic landing gear extension can be accomplished by using either the alternate landing gear blow down system or the alternate landing gear free fall system.
It is recommended that the blow down system be used prior to the free fall system. Air pressure to operate the blow down system is supplied by the "GEAR AIR" emergency air bottle and is controlled by the "EMERGENCY BLOW DOWN GEAR" lever on the right side of the center pedestal. Air pressure to operate the free fall system is supplied by the "BRAKE AIR" emergency air bottle and is controlled by the "EMERGENCY FREE FALL GEAR LEVER" located on the right side of the center pedestal forward of the blow down lever. The manual states that whenever alternate landing gear extension is to be selected, the landing gear selector switch should be placed in the down position and the GEAR circuit breaker should be pulled.
When the EMERGENCY BLOW DOWN GEAR lever is pushed down, air pressure from the GEAR AIR emergency bottle is admitted to the blow down system through the lever actuated blow down valve. If the air pressure is greater than the landing gear system hydraulic pressure, shuttle valves in the landing gear system will reposition to admit air pressure to the landing gear system inboard main landing gear door and door uplock actuators, the main landing gear actuators, the nose landing gear uplock and gear actuators, the landing gear control valve, and the door control valve.
According to the Learjet 55 Aircraft Flight Manual, under the Abnormal Procedures section for Alternate Gear Extension, flight crews are instructed to place the landing gear selector switch to the down position and pull the landing gear circuit breaker. The EMERGENCY BLOW DOWN GEAR Lever is to be pushed full down until the lever latches and the three landing gear LOCKED DOWN light illuminate. If the LOCKED DOWN lights do not illuminate, the flight crew is instructed to push full down on the EMERGENCY FREE FALL GEAR Lever until it latches. According to the procedure, the landing gear will extend and lock within approximately 15 seconds and the landing gear LOCKED DOWN lights should illuminate.
If any gear is not down and locked, the GEAR UP LANDING procedure should be referenced. The Aircraft Flight Manual's procedures for a GEAR UP LANDING recommends that the flight crew "select a long, wide runway," and should "plan the descent to ensure minimum fuel remaining on the aircraft."
According to the pilot's manual, with the navigation lights on, the instrument panel avionics annunciator lights, most instrument panel lights, pedestal lights, and landing gear position lights will automatically dim.
The flight crew obtained their last weather condition update from SoCal approach approximately 10 minutes prior to the accident. The weather conditions given in that report were wind from 120 degrees at 4 knots; visibility 6 statute miles in mist; few clouds at 100 feet agl; temperature 14 degrees Celsius; dew point 12 degrees Celsius; and an altimeter setting of 30.08 inches of mercury.
The Fairchild GA100 tape cockpit voice recorder (CVR) was sent to the audio laboratory of the NTSB on December 22, 1998. The CVR committee convened on April 2, 1999, and a transcript was prepared for the entire 32:01 minute recording. The exterior of the CVR showed no evidence of structural damage, and the interior and tape sustained no apparent heat or impact damage. The recording consisted of four channels of good quality audio information. The first channel contained the co-pilot's audio panel information. The second channel contained the audio information from the cockpit area microphone. The third radio channel contained the pilot's audio panel information. The fourth channel did not contain any usable audio information (nor was it required for this aircraft per Federal Aviation Regulations). Timing of the recording was established through a correlation to Southern California Air Traffic Control transmissions, supplied by the FAA.
From 0851:45 to 0852:28, the CVR recording speed changed; specifically the recorder decreased speed, which caused the recording to sound fast during normal playback. In order to decipher the conversation, the tape playback speed was varied to approximate normal playback speed. Although timing during this segment was correlated as accurately as possible to normal voice speed, there was no means to verify the correlation to local time. The recording ended at 0856:32, 22 seconds after a sound of impact was recorded on the CVR.
As part of the Safety Board's accident investigation process, the crewmembers were invited to review the CVR transcript and suggest corrections or additions. They have not responded to the invitation.
WRECKAGE AND IMPACT INFORMATION
The aircraft was examined on December 19 and 20, 1998, by an NTSB investigator, the FAA, and air safety investigators from Bombardier Aerospace Learjet, Inc. It was reported to the Safety Board that the flight crew had reentered the cockpit after the accident; however, it is not known if anything was moved or altered. The airplane sustained structural damage to its bottom side and right outboard wing, and minor damage to the landing gear doors and the left and right wing flaps. Four circuit breakers were found in the opened position; however, one of the circuit breakers was tie wrapped open. Of the three others that were found open, one was the GEAR circuit breaker. The landing gear system was examined and it was noted that the three landing gear actuator shuttle valves were found in the air position; however, the three main landing gear uplock actuator shuttle valves were found in the hydraulic position. The two main landing gear inboard door actuator shuttle valves were also found in the hydraulic position. The emergency gear extend air valve lever was not in the down and locked position, instead, it was found approximately 2/3 of the way down. According to Learjet representatives, this position would not supply continuous air pressure to the landing gear blow down system. The emergency free fall landing gear extension lever was found in the up (not actuated) position. The landing gear control panel was found to have a loose electrical connector. The connector was found approximately 0.10-inch from being completely connected. No current limiters or circuit breakers on the power distribution panel were open. General examination of the electrical system revealed that the No. 1 (left) battery was leaking through a crack in the battery case.
TESTS AND RESEARCH
The aircraft was lifted by two fork lifts and were placed on jacks. The landing gear blow down system was then activated and the landing gear position lights were observed utilizing the aircraft's emergency battery power. All shuttle valves moved to the air position and the landing gear locked in the down position. Testing of the loose landing gear electrical connector resulted in an intermittent connection for both the normal landing gear circuit and the emergency battery circuit.
The following items were tested at the Bombardier Aerospace Learjet Inc., facility in Wichita, Kansas, on January 13, 1999, under the supervision of a Safety Board investigator, the FAA, and representatives from Bombardier and Concorde Battery:
Generator Control Panel
Current Limiter Panel
Left Voltage Regulator
Right Voltage Regulator
Landing Gear Control Valve
Flap Control Valve
Left Hydraulic Pump
Right Hydraulic Pump
Left Generator Interface Box
Right Generator Interface Box
Landing Gear Selector Switch Assembly
The batteries, voltage regulators, generator control panel, and the generators were connected to a test stand and run as a system. The batteries were turned on and a simulated flight load of 50 amperes was applied for 33 minutes. A simulated battery dual engine start load of 100 amps was applied for 3 minutes then reduced to the 50-amp load. The generator switches were placed in the GEN position at a bus voltage of approximately 12 VDC and both generators supplied charging current to the batteries of 200+ amps to the undamaged battery and approximately 5.5 amps to the damaged battery. The generators were turned off and the batteries continued to discharge for another 20 minutes via the 50-amp load until bus voltage reached approximately 9 VDC, at which point the voltage was too low to close the generator relays. Both generators tested within operating specifications, and resistance checks and output ability were within limitations. Both generator interface boxes were bench checked and passed all requirements. The generator control panel functioned normally.
The landing gear control valve was connected to a test bench and checked for operation in the landing gear up, landing gear down, and landing gear blow down positions. All checks were within functional requirements and the valve continued to operate down to a hydraulic pressure of 100 psi. The flap selector valve was found to operate properly and tested within the functional requirements. Both hydraulic pumps were tested within operational specifications. The left hydraulic pump produced 5.0 gallons per minute (GPM) at 1,400 psi and the right hydraulic pump produced 4.9 GPM at 1,270 psi.