Type development continued with the Models 25D and 25G, which included more advanced CJ610-8A engines and a ceiling increase to 51,000 ft (16,000 m).

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.

[3] The electrically operated RPM tachometer consists of a signal generator on the engine and an indicator located in the centre of the instrument panel.

The pulsating DC voltage is averaged and forwarded through the selector switch to the fuel flow indicator.

On aircraft 25-061 through 25-180 the engine driven hydraulic pumps supply fluid under a pressure of 1,500 psi (10.3 MPa).

Two motor-driven shutoff valves will stop hydraulic flow to the engine-driven pumps in case of an emergency.

Nose wheel steering is electronically controlled by the rudder pedals, utilizing the synchro principle.

Hydraulic pressure for retraction and extension of the gear is transmitted by a system of tubing, hoses and actuating cylinders and is electrically controlled by limit switches and solenoid valves.

Two shuttle valves in the pressure lines prevent fluid feedback between the pilot's and copilot's pedals.

The tip tanks provide additional fuel capacity to enable longer times aloft.

When the tank is full, a float switch de-energizes the wing boost pumps and closes the valve.

The control wheels operate the elevator and ailerons mechanically through a system of cables, pulleys, push-pull tubes and bell cranks.

Trim functions, microphone keying, autopilot override and steering system switches are located on the control wheels.

The vanes provide regulated voltage input to the angle-of-attack transducers, modified by a stall warning bias box to compensate for flap position.

When both angle-of-attack transducer vanes increase to 5% above stall, the pitch servo commands an aircraft nose down attitude.

The indicator face is divided into green (safe), yellow (caution) and red (danger) segments.

Engine bleed air is admitted through a flow control valve to a heat exchanger.

The H-valve position can be adjusted by the crew to increase or reduce the amount of bleed air cooling at the heat exchanger.

The refrigeration system consists of a compressor, receiver dehydrator and evaporative cooler located above the baggage compartment.

During ground operations, a solenoid limits the pressure differential to 0.25 psi (17 hPa) in order to ensure normal functioning of the door and emergency exit.

The engine fire system is of the continuous-element type and will provide a FIRE warning indication to the crew in the event that the rear nacelle area temperature exceeds 510 °F (266 °C) or if the forward nacelle area temperature exceeds 480 °F (249 °C).

This point is near the aircraft centre of gravity and minimizes weathervaning when the chute is deployed under crosswind conditions.

The spoilers provide an effective means of increasing normal rates of descent and may be used as a drag device to achieve rapid airspeed deceleration.

At this speed, the Learjet 25 glides approximately 26 nautical miles (48 km) for each 10,000 ft (3,000 m) of altitude loss.

Pilot workload is high and approach, landing and takeoff speeds are above average for civilian aircraft.

To become a medevac aircraft, the starboard seating is removed to allow for a stretcher as well as oxygen bottles and intravenous drip equipment.

In 1974 the Peruvian Air Force purchased two 25Bs with a belly pod that contained an aerial survey camera.

In 2013, the FAA modified 14 CFR part 91 rules to prohibit the operation of jets weighing 75,000 lb (34,000 kg) or less that are not stage 3 noise compliant after December 31, 2015.

Any Learjet 25s that have not been modified by installing noise compliant engines or "hushkits" are not be permitted to fly in the contiguous 48 states from December 31, 2015.

During a series of demonstration flights lasting from June 9 to 18, 1982, the 25G broke a number of long-distance speed and fuel consumption records.