Learjet 25

The Learjet 25 is an American ten-seat (two crew and eight passengers), twin-engine, high-speed business jet aircraft manufactured by Learjet. It is a stretched version of the Learjet 24.

Development

thumb|right|A Learjet 25B

The first Model 25 flew on August 12, 1966, and the first delivery was in November 1967. The Learjet 25A got its type certification on May 19th, 1970, while the 25B and 25C were type certified on September 4th 1970, and the later D and F models were certified on May 20th, 1976.

The Learjet 25 is similar to the Model 24 but is longer, allowing for three additional passengers. In 1970 the Learjet 25B was produced along with the Learjet 25C in the same year. Type development continued with the Models 25D and 25G, which included more advanced CJ610-8A engines and a ceiling increase to .

By 2019, 1970s Learjet 25s were sold for under $200,000.

Design

Engines

thumb|Learjet 25 about to take-off

Two General Electric CJ610-6 single-rotor axial-flow turbojet engines are pylon-mounted on the aft fuselage. Each engine is rated at of thrust at sea level. The engine has of an eight-stage axial-flow compressor directly coupled to a two-stage turbine, a through-flow annular combustion system, variable inlet guide vanes, controlled compressor interstage bleed, exhaust nozzle and an accessory drive system. Starting ignition is provided by a dual output capacitor-discharge system. As the ignition cycle is completed, the igniter plugs cease sparking and combustion becomes self-sustaining. A fuel control metering system selects the rate of fuel flow to the engine combustor.

The electrically operated RPM tachometer consists of a signal generator on the engine and an indicator located in the centre of the instrument panel. Dial markings are based on percent of maximum allowable engine speed. The large markings are graduated in 2% increments from 0% to 100% and the small dial is graduated in 1% increments from 0% to 10% to allow the pilots to accomplish more precise engine speed settings.

The engine pressure ratio (EPR) system enables the pilot to obtain power required to meet certified aircraft performance without exceeding engine limitations. The engine compressor inlet and turbine discharge pressures are sensed by the EPR transmitter and transformed into an electrical signal that is transmitted to the EPR indicator.

Fuel flow is indicated via a fuel flow system. The fuel flow through a rotor-turbine at each engine causes the rotor to spin and a pickup coil emits pulses as the rotor blades pass through the coil field. The pulsating DC voltage is averaged and forwarded through the selector switch to the fuel flow indicator.

Hydraulics

The landing gear, brake, flap and spoiler systems are hydraulically operated. On aircraft 25-061 through 25-180 the engine driven hydraulic pumps supply fluid under a pressure of . System pressure is maintained at by a pressure regulator. On aircraft 25-181 and subsequent the variable volume engine driven pump delivers fluid under a pressure of to the system and static pressure is maintained at . Over pressurization is prevented by a pressure relief valve which opens at . A pre-charged accumulator dampens and absorbs pressure surges. Two motor-driven shutoff valves will stop hydraulic flow to the engine-driven pumps in case of an emergency. The valves are controlled by the FIRE switch and activation of these valves are indicated with pinhead lights located in the cockpit next to the FIRE switch.

On aircraft equipped with an auxiliary hydraulic pump, the hydraulic pump switch located at the lower center of the instrument panel activates the auxiliary hydraulic pump to provide in-flight standby hydraulic pressure. A pressure switch will energize the pump if hydraulic pressure falls below a preset level and de-energize the pump when pressure returns to normal. A duty cycle of 3 minutes on and a cooling period of 20 minutes off is required to avoid overheating the pump motor.

Pneumatics

The Learjet 25A was the first to use the signature pneumatic clam-shell style cabin door design that has been used on all Learjet products since. Designed for the Learjet 25 in 1963 by Bill Lear to minimize the number of stairs for the passenger to climb. The door is opened by pneumatic pistons holding up the upper part of the clamshell, and a pair of pistons slowly letting down the bottom part of the clamshell.

Learjet 25A

FAA certified on May 19th, 1970.

On 2 March 1996, a privately chartered Learjet 25D had the Brazilian comedy rock band Mamonas Assassinas were killed while approaching Guarulhos International Airport, the major airport serving the city of São Paulo. The plane made a previous landing attempt and was approaching the airport for a second attempt. The aircraft extended its downwind leg and crashed into the Cantareira mountain range just north of the airport. All five members of the band were killed, along with two additional passengers and both crew members. The investigation showed several errors that led to the accident, including fatigue of the crew of the air taxi company hired for the transport of the rock band after a 17-hour duty cycle.
On December 9, 2012, a privately chartered Learjet 25 made an extreme departure from level flight while carrying seven occupants, including Mexican-American singer Jenni Rivera. The aircraft departed Monterrey at 3:15 a.m. for a planned one-hour flight, with Toluca, a city just outside Mexico City, as its destination. According to authorities, communication with the plane was lost 10 minutes after departure. The wreckage of the aircraft was found in the municipality of Los Tecojotes, and rescue personnel confirmed that all aboard were killed. From the lack of scatter of the wreckage, the aircraft is believed to have impacted at a vertical angle of over 80 degrees from horizontal.
On April 10, 2014, a privately owned Learjet 25D was destroyed on the ground by Venezuelan forces. The airplane had reportedly departed Belém, Brazil without a flight plan and with the transponder turned off. The Venezuelan armed forces forced the Learjet to land on suspicion the aircraft was being used for "illicit activities", possibly involving drugs smuggling. The airplane was destroyed on the ground.
On May 17, 2017, a Learjet 25B registration XA-VMC operated by the company Aerotransportes Huitzilin S. A. de C. V. crashed at 3:26 p.m. local time shortly after taking off from Toluca International Airport, Mexico bound for Durango. Both pilots died.

Specifications (Learjet 25D)

References

Taylor, John W. R. Jane's All The World's Aircraft 1976–77. London:Jane's Yearbooks, 1976. .

External links

A history of the LJ23-LJ29 series on Airliners.net
Listing of LJ25 accidents in the ASN Aviation Safety Database