M4006-4 - Honeywell Aerospace Hobbs Hour Meter Pressure Switch

M4006-4 – Honeywell Aerospace Hobbs Hour Meter Pressure Switch

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Overview

The Honeywell M4006-4 is a premier, OEM-grade electromechanical pressure switch from the Hobbs product line, the brand that originated the aircraft hour meter. This is a high-precision instrument, not a simple switch, engineered to provide exceptionally reliable and accurate automatic activation of an aircraft's flight time recorder. Its function is to translate the presence of normal engine oil pressure into a closed electrical circuit, thereby starting the Hobbs meter. When the engine is shut down and oil pressure decays, the switch opens the circuit, stopping the meter. The accuracy of this component is fundamental to the entire maintenance and operational life tracking of an aircraft.

Built to Honeywell's exacting aerospace standards, the M4006-4 features a robust, environmentally sealed housing to protect its internal components from the harsh engine compartment environment. The switch's internal diaphragm and contact mechanism are calibrated to a precise actuation pressure setpoint, ensuring that flight time is logged consistently and correctly, flight after flight. For any aircraft requiring an accurate, reliable, and long-lasting Hobbs meter trigger, the genuine Honeywell M4006-4 is the industry standard for quality and performance.

Key Features

• Genuine Honeywell/Hobbs OEM Part: The industry benchmark for quality and reliability, from the original manufacturer of the hour meter.

• High-Precision Actuation: Factory-calibrated to a tight pressure tolerance, ensuring repeatable and accurate activation and deactivation of the hour meter.

• Exceptional Reliability: Engineered with a high-cycle life diaphragm and contacts, designed to withstand tens of thousands of pressure and thermal cycles without setpoint drift.

• Environmentally Sealed Construction: Protects the sensitive internal electrical contacts from oil, moisture, and contaminants, preventing premature failure.

• Broad OEM Acceptance: Specified as the component of choice by numerous general aviation aircraft manufacturers.

Technical Specifications

• Part Number: M4006-4

• Component Type: Electromechanical Oil Pressure Switch

• OEM Manufacturer: Honeywell Aerospace (Hobbs Division)

• Application: Hobbs Meter / Flight Time Recorder Activation

• Switch Type: Normally Open (NO), Single Pole, Single Throw (SPST)

• Actuation Pressure: Calibrated to close at a specific setpoint, typically in the 30-40 PSI range. The exact pressure setpoint is proprietary to the Honeywell specification and should be matched to the aircraft's requirements.

• Thread Size: 1/8"-27 NPT (National Pipe Taper)

• Electrical Connector: #8-32 UNC Stud Terminal

• Voltage Rating: Compatible with 12V and 24V DC aircraft electrical systems.

Aircraft Compatibility

The Honeywell M4006-4 is a widely specified OEM and PMA part used across the general aviation industry on aircraft equipped with Lycoming, Continental, and other piston engines. Manufacturers include but are not limited to:

• Piper Aircraft

• Mooney International Corporation

• Cirrus Aircraft

• Commander Aircraft

• Various Experimental Aircraft

Note: While this is a common industry part, the aircraft's specific Illustrated Parts Catalog (IPC) is the final and absolute authority for determining part applicability.

Applications

• Primary Flight Time Logging: Serves as the primary automatic switch for activating and deactivating the Hobbs meter based on engine oil pressure.

• Accurate Maintenance Tracking: Provides the foundational data for tracking all time-based inspections (100-hour, annual), component TBOs, and AD compliance.

Why Choose M4006-4?

In aviation maintenance, time is everything. The accuracy of the Hobbs meter is critical for both safety and cost management. The genuine Honeywell M4006-4 is a calibrated instrument designed for long-term stability. Using a non-certified or low-quality switch can lead to significant errors in time logging. A switch with an incorrect or drifting setpoint can either fail to record flight time, creating a major safety hazard by allowing the aircraft to exceed inspection limits, or it can run excessively, leading to unnecessarily early and costly maintenance. The proven reliability and precision of a genuine Hobbs switch is a low-cost investment in the safety, compliance, and proper management of any aircraft.

The engineering principle that defines the Honeywell M4006-4 is its high degree of repeatability. The switch is designed as a calibrated instrument where the internal sensing diaphragm and spring assembly have a known and stable spring rate (k). The actuation point is a function of this spring rate versus the force applied by the engine oil pressure (F = P × A). Honeywell's design and material selection—utilizing a stable elastomer for the diaphragm and a spring material with a low thermal coefficient of expansion—ensures that this balance of forces remains constant, providing a setpoint that does not drift significantly over thousands of thermal and pressure cycles. This ensures that the Hobbs meter is triggered at nearly the exact same pressure on every flight for the entire service life of the switch, providing the consistent, repeatable performance required for a certified aircraft instrument.

Note: The M4006-4 is a critical instrument for aircraft maintenance tracking. Installation must be performed by a certified A&P mechanic. Use an appropriate, aviation-grade thread sealant on the NPT threads to ensure a leak-free seal. Do not overtighten, as this can damage the switch housing. After installation, perform an engine run-up to verify the proper operation of the Hobbs meter and inspect for oil leaks.

Documentation

No public-facing OEM specification sheet was located for this specific part number. All authoritative installation and application data are contained within the official Aircraft Maintenance Manual and Illustrated Parts Catalog (IPC) for the applicable aircraft model.

**** PLEASE NOTE, THIS PART IS LEGACY AND IS NO LONGER IN PRODUCTION. IF REQUIREMENT IS FOR BEECH APPLICATIONS, USE ALTERNATE 76575-4 PART NUMBER. ALTERNATE VERIFIED IN ALL TEXTRON IPCs. ****

Product Overview

A switch which is actuated by changes in pressure of any gas or liquid or by changes in a vacuum acting upon its sensing element. Excludes baroswitch; switch, pressure-thermostatic; and switch, sensitive.

Characteristics

**Technical Datasheet [Click Here]