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48C48641 – Bombardier OEM L5 Gear Selector Valve Assembly
Available now on the Airparts.aero Marketplace.
The Bombardier 48C48641 is a high-precision, flight-critical hydraulic selector valve engineered for the landing gear system of the Learjet 45 (L45) and Learjet 75 (L75) series aircraft. As the primary control interface between the pilot's landing gear handle and the hydraulic actuators, this valve is responsible for directing 3,000 PSI of hydraulic fluid to either the "Extend" or "Retract" side of the main and nose landing gear circuits. The 48C48641 ensures that the landing gear sequence—including the opening and closing of gear doors—occurs in the precise mechanical order required for safe flight operations.
Constructed from aerospace-grade aluminum alloy and featuring hardened stainless steel internal spools, the 48C48641 is designed to handle the high-pressure surges and rapid cycling characteristic of "cycle-heavy" regional and business flight profiles. This valve assembly often incorporates internal thermal relief valves and "check" logic to maintain the gear in the "Up-and-Locked" position against aerodynamic air-loads, even in the event of a momentary drop in system hydraulic pressure.
Key Features
Precision Spool-and-Sleeve Design: Utilizes ultra-tight tolerances to minimize internal "blow-by" leakage, ensuring that hydraulic pressure is efficiently translated into mechanical movement without wasting pump capacity.
Integrated Sequencing Logic: Specifically ported to manage the timing between landing gear door actuation and strut extension, preventing mechanical interference between the airframe and the gear.
High-Pressure Resilience: Rated for a nominal operating pressure of 3,000 PSI, with a burst-pressure safety factor that meets or exceeds FAA/EASA Part 25 certification standards.
Corrosion-Resistant Architecture: Finished with a hard-anodized coating to resist the aggressive chemical properties of Skydrol (Phosphate Ester) hydraulic fluids.
Direct-Action Feedback: Designed to provide consistent "feel" and response time, ensuring the gear transit time remains within the aircraft's certified limits across a broad temperature range (–55°C to +70°C).
Technical Specifications
Part Number: 48C48641
Manufacturer: Bombardier Aerospace (OEM) / Often produced by Woodward or Tactair
Component Type: Landing Gear (L/G) Selector Valve
Operating Pressure: 3,000 PSI (Standard System)
Fluid Compatibility: Skydrol LD-4, Skydrol 5, or equivalent Phosphate Ester fluid
Material: Anodized Aluminum Housing / Stainless Steel Internals
Certification: FAA-PMA / EASA Form 1 (with OEM Traceability)
Application Group: Landing Gear Hydraulics (ATA 32)
Aircraft Compatibility
Bombardier Learjet 45 (L45): All standard and XR variants.
Bombardier Learjet 40: (Short-fuselage variant).
Bombardier Learjet 70 / 75: The modernized L5/L7 series.
Note: The 48C48641 is a specific "L5" series designation. Always verify the part number and "Mod Status" against your aircraft’s Illustrated Parts Catalog (IPC) Section 32-31 to ensure compatibility with your specific serial number.
More specifically:
- Learjet 24
- Learjet 25
- Learjet 28
- Learjet 29
- Learjet 31
- Learjet 35
- Learjet 36
- Learjet 55
- Learjet 60 / 60XR
Applications
The 48C48641 is utilized for Hydraulic Flow Direction. Its primary roles include:
Gear Extension/Retraction: Governing the flow of fluid to the landing gear actuators.
System Isolation: Maintaining pressure in the "Up" line during cruise to keep the gear stowed without mechanical locks (where applicable).
Ground Testing: Serving as the central point for functional "swing tests" during scheduled maintenance inspections.
Why Choose 48C48641?
Choosing the genuine Bombardier 48C48641 is essential for preventing "Gear-in-Transit" warnings or uncommanded gear drops. Non-OEM or improperly overhauled selector valves can suffer from "spool-sticking" due to seal swelling or microscopic debris, which can lead to asymmetric gear extension—a critical safety risk. The 48C48641 is calibrated to the specific volumetric flow rate of the Learjet’s hydraulic pumps, ensuring that the gear retracts and extends symmetrically to maintain aircraft aerodynamic balance.
The 48C48641 operates on the principle of Fluid Power Directional Control governed by the Continuity Equation ($Q = A \cdot v$). When the pilot moves the gear handle, the internal spool of the 48C48641 shifts, aligning high-pressure ports with the "Extend" or "Retract" manifold. Because the landing gear is a large-mass system, the valve must manage Pressure Spikes caused by the sudden stop of the heavy gear at the end of its travel. The 48C48641 utilizes precision-tapered spool lands to provide "metering," which cushions the hydraulic shock and prevents structural fatigue in the actuator mounts. The internal seals are made of Ethylene Propylene (EPR), specifically chosen for their chemical compatibility with Skydrol, ensuring zero external leakage over thousands of flight hours.
Note: This is a flight-critical hydraulic component. Installation must be performed by a certified A&P/AME. Prior to installation, the hydraulic system must be fully depressurized and the gear must be physically pinned on jacks. Post-installation, a full "Landing Gear Swing Test" (including emergency extension checks) is mandatory. Ensure all hydraulic fittings are torqued to the AMM specification to prevent high-pressure "pinhole" leaks.
