MS25331-1 - Diamount Inline Push To Test Lamp Indicator Assembly

MS25331-1 – Mil-Spec Push-To-Test Lamp Indicator Assembly

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Overview

The MS25331-1 is a military-specification, watertight, press-to-test indicator light designed for the most demanding aerospace and defense applications. This is a flight-critical cockpit instrument, not a simple light. Its purpose is to provide unambiguous visual annunciation for the aircraft's most critical warning systems. The MS25331-1 part number specifically designates a Red lens for Warning alerts and is engineered for 28 Volt DC systems. The integrated "push-to-test" functionality is a paramount safety feature, allowing the flight crew to verify the integrity of the indicator and its bulb at any time, eliminating the dangerous ambiguity of a dark indicator.

Constructed with a rugged, black anodized aluminum body and fully sealed against moisture, this indicator is built to withstand the vibration, temperature cycling, and harsh environment of any cockpit. It is the standard for reliable annunciation in Caution and Warning Systems (CWS), used to alert the crew to immediate, safety-of-flight conditions such as engine fire, hydraulic failure, or unsafe landing gear configuration. For guaranteed performance and airworthiness, the certified MS25331-1 is the definitive standard.

Key Features

• Mil-Spec Certified: Manufactured and tested in strict accordance with MS25331, guaranteeing performance, durability, and interoperability.

• Integrated Push-To-Test Function: Allows the pilot to confirm bulb and circuit integrity with a simple press of the lens, a critical pre-flight and in-flight safety check.

• Watertight Construction: Fully sealed with O-rings and gaskets to prevent the intrusion of moisture, fluids, or dust, ensuring reliability in the most demanding environments.

• Red "Warning" Lens: The red color is the aerospace standard for annunciating a hazardous condition requiring immediate crew attention and corrective action.

• Rugged Anodized Aluminum Body: Provides a durable, corrosion-resistant, and lightweight housing for the lamp and switch mechanism.

Technical Specifications

• Part Number / Specification: MS25331-1

• Component Type: Indicator, Light, Press-To-Test, Watertight

• Lens Color (-1): Red

• Voltage Rating (-1): 28 VDC

• Compatible Lamp: Incandescent T-1 3/4 Midget Flange Base, P/N MS25237-327 (or FAA-approved LED equivalent).

• Body Material: Black Anodized Aluminum Alloy.

• Mounting: Panel mounts in a keyed hole.

• Governing Specification: MS25331.

Aircraft Compatibility

• Universal Aerospace Application: This is a standard mil-spec indicator light used in the cockpit and system control panels of virtually every class of military, commercial, and general aviation aircraft. It is specified by OEMs including:

  • Boeing, Lockheed Martin, Northrop Grumman, Textron Aviation (Cessna, Beechcraft), Bombardier, Piper, and countless others.

Note: The correct indicator for any specific system must be verified against the aircraft's wiring diagrams and maintenance manuals.

Applications

The MS25331-1, as a red warning indicator, is used for the most critical annunciations on an aircraft, including but not limited to:

• Engine Fire / Overheat Warning

• APU Fire Warning

• Landing Gear Unsafe / In Transit

• Low System Pressure (Hydraulic, Oil, Fuel)

• High System Temperature (Hydraulic, Oil)

• Cabin Pressure Altitude Warning

Why Choose MS25331-1?

A pilot's ability to respond to an emergency is dependent on the unambiguous and reliable function of the aircraft's warning systems. A failed indicator light can mask a developing catastrophic failure. The MS25331-1 is a certified component built for this no-fail mission. Unlike commercial-grade indicators, it is proven to resist vibration, moisture, and temperature extremes. The integral push-to-test feature is a critical safety function that is often missing from non-certified parts. Using a genuine, traceable mil-spec indicator is a fundamental requirement for the safety and airworthiness of any certified aircraft.

The engineering principle behind the MS25331-1's press-to-test feature is a foundational concept in system safety and human factors engineering: the elimination of "fail-silent" faults. A standard indicator light has two states: illuminated (indicating a condition) and dark. A dark state is ambiguous; it can mean either "system normal" or "indicator has failed." This ambiguity can lead a flight crew to believe all systems are nominal when, in fact, a warning system has become inoperative. The press-to-test function adds a third, diagnostic state. It incorporates a momentary switch that, when actuated by pressing the lens, creates an independent electrical path that bypasses the system sensor and connects the lamp directly to a test power source. This action provides an immediate and unambiguous test of the lamp's and the local wiring's integrity. It allows the crew to differentiate between a "normal" state and a "failed indicator" state, thereby ensuring the reliability and trustworthiness of the entire Caution and Warning System.

Note: The MS25331-1 is a flight-critical cockpit component. Installation must be performed by a certified A&P mechanic or avionics technician. Ensure that both the primary system logic and the push-to-test circuit are wired correctly in accordance with the aircraft's wiring diagram. The incandescent lamp (MS25237-327) is a replaceable component.

Documentation

• MS25331: The military standard sheet defines all dimensional, performance, and material requirements for this series of indicators and is publicly available through various online mil-spec libraries such as the Defense Logistics Agency ASSIST database.