Hangar Talk: Editorial
What's Really Involved in the Certification of that Jet? (Pg. 2)
Learjet 35a Safety Certification Highlights
WEIGHT AND CENTER OF GRAVITY
Weight and C.G. certification require extensive testing under a variety of weather and weight conditions. Certain criteria must be met for atmospheric and weight/c.g. variables such as:
Between these two temperatures, the relative humidity must vary linearly.
Structural Members: The Learjet structural members, throughout the aircraft, are in close proximity of each other. This design and construction offers a FAIL-SAFE structure. If a structural member should fail, this will not create a catastrophic situation since the nearby structural members are capable of absorbing this additional load. The fuselage is built around a main keel beam in the cabin area and utilizes round shape frames, which are ideal for a pressurized vessel.
Cabin Door: The Learjet cabin door is designed with two halves (an upper half and a lower half), which are locked together with ten heavy steel pins. When the door is closed, it is an integral part of the cabin structure.
Amongst other things, FAR 25.1351 specifies that:
Compliance with the above requirements is provided by a dual generator system. Each engine has a respective DC generator rated at 30V and 400AMPS. Both generators provide DC power to all the required DC (and, through inverters, AC busses). However, with the failure of one generator, the remaining generator can provide the same buss powering. Therefore, the failure of one generator will not adversely affect the total electrical systems in flight.
If both DC generators should fail in flight, the aircraft's two 24VDC batteries will provide an additional backup (redundancy) to a double-generator failure for approximately 30 minutes in night IFR conditions.
If both DC generators, and both ship's batteries become depleted, a standby emergency battery will provide DC power to only a few select systems. These are the standby gyro and its light, the landing gear circuit, the flaps circuit, and landing gear green locked-down lights. This battery will last 3:45 minutes in the STANDBY position (gyro and light only), or: 30 minutes in the ON position (powering all the above components). Should the standby battery become depleted, there would be no additional sources of electrical power in the aircraft.
Means of providing control and monitoring of the electrical systems is provided by switches and gauges accessible to the flightcrew. Each respective generator has a switch and a reset switch for generator control. Each battery also has a respective switch that can be placed in the ON or OFF position.
Should an engine fail during takeoff in the Learjet 35a, certification under Part 25 guarantees a positive climb gradient on the remaining engine, provided certain criteria are met. The criteria must be the most restrictive of the following:
If the aircraft is above the maximum weight as required from above, there will be no guarantee of the climb performance advertised in the performance charts.
The fuel system in the Learjet 35a is self-sustaining once the engines have been started. The fuel is supplied through Jet Pumps (Motive Flow System). Jet pumps have no moving parts and require no electrical power. They operate by the Venturi Principle (pressure differential causes the fuel to enter the pump). Therefore, a total loss of DC electrical power in flight will not adversely affect the engine fuel system. Further, the aircraft can be descended below 25,000 feet, if necessary, where the engines can suction feed fuel through their respective fuel pumps.
Fuel Jet Pump
Additional requirements of the fuel system include venting, filtering, and draining capabilities. Since the Learjet 35a does not have fuel heaters, a fuel anti-icing additive must be added to the fuel to prevent fuel icing at higher altitudes.Continue =>
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