MIL-STD-1760 Aircraft/Store Connectors:
Classes, the D38999/31 Umbilical & Cross-Reference

What MIL-STD-1760 Actually Standardizes

MIL-STD-1760 — properly titled Aircraft/Store Electrical Interconnection System (AEIS) and issued as a Department of Defense Interface Standard — defines the electrical, optical, mechanical and message-level interface between a military aircraft and everything it carries. "Stores" is deliberately broad: guided munitions such as GBU-31 JDAM, air-to-air missiles, targeting and reconnaissance pods such as the AN/AAQ-14 LANTIRN, and drop tanks all fall under it.

Before the standard, every new store arrived with its own proprietary wiring, connector and signalling convention. The aircraft's Stores Management System (SMS) had to be re-integrated for each addition — an engineering and logistics burden that scaled badly. MIL-STD-1760 replaced that with one interface definition: signal characteristics, connector type and pin assignment, all fixed by the standard. Development first appeared in the 1980s and the document has been revised several times since:

Three interface points are defined, and knowing which one your drawing refers to is the difference between a correct and an incorrect quote:

• ASI — Aircraft Station Interface. Where the aircraft (or its pylon/rack) meets the store.
• MSI — Mission Store Interface. The store-side half of the interface.
• CSI — Carriage Store Interface. Present in more complex architectures where an external rack carries several stores; the standard defines requirements here as well as at the ASI and MSI.

The Connector: A Sheet 31 Lanyard-Release Plug

The 1760 primary (hand-mated) interface is not a unique connector design — it is a defined configuration of an existing mil-spec circular. Type 1 CSI and MSI connectors must be intermateable with MIL-DTL-38999/31, shell size 25, polarization key identification N. In other words: a MIL-DTL-38999 Series III triple-start threaded coupling with a lanyard-release mechanism, in a fixed shell size, a fixed insert arrangement, one keying position, and an environmental class suitable for carriage-store duty.

The lanyard is the functional heart of it. When the store is ejected, the lanyard stays with the aircraft and pulls the plug free of the receptacle in one motion, with no crew action and no damage to the receptacle. The catalogued release forces for shell size 25 are deliberately tightly bounded — too light and the connector releases under vibration, too heavy and the store separation event is disturbed:

Insert Arrangement 25-20: What the 30 Contacts Are

Shell size 25 with insert arrangement 25-20 is the arrangement the 1760 signal set was designed around. It is a hybrid layout — signal, power, coax and twinax contacts in one insert — and its contact population is fixed by the specification, not by the supplier:

Note the consequence for substitution: a "38999 Series III shell 25 plug" catalogued under a different insert arrangement (25-4, 25-19, 25-35 and so on) has the same shell and thread but the wrong contact map. The 1760 pin assignment only exists in 25-20. Insert arrangement, not shell size, is the controlling attribute.

Class I vs Class II Interfaces

Not every store needs the full signal set — a JDAM does not require the same bandwidth as a fibre-channel sensor pod. The standard resolves this by defining interface classes, and this choice cascades directly into which contacts are populated and whether the store needs optical termini at all.

In practice the aircraft supports most of the MIL-STD-1760 signal set while the store accommodates only what its mission needs, so stores operate on a subset of interface signals. That asymmetry is why two stores with identical connectors can have completely different wiring harnesses behind the panel.

The Signal Set in Plain Terms

High-Speed 1760 (SAE AS5653)

Revision E of the standard added a genuine gigabit channel for digitized video, terrain maps, target imagery and program-file uploads. Known as High-Speed 1760, it is defined by SAE AS5653: a Fibre Channel based interface running at 1.0625 Gbit/s over a pair of 75 Ω coax cables, reusing the High Bandwidth 2 and High Bandwidth 4 pins that existed in the insert but had never been assigned. Upper-layer protocols are FC-AE-1553 (MIL-STD-1553 adapted to Fibre Channel, for command/control and file transfer) and FC-AV (video and audio). The takeaway for a harness engineer: the connector did not change in Revision E — the contact assignment did. A 25-20 insert built to the current standard can carry it.

Type 1 vs Type 2 Connectors: Hand-Mated vs Rail-Launch Blind Mate

Two connector families implement the standard, and they solve different mechanical problems.

What to Specify on a 1760 Connector RFQ

1760 requisitions fail most often on incomplete mechanical definition rather than on electrical questions. Send all of the following and the quote comes back correct the first time:

• Interface point — ASI, MSI or CSI. It changes which half of the pair you are buying.
• Connector type — Type 1 (D38999/31 lanyard release, hand-mated) or Type 2 (MIL-DTL-83538 blind mate).
• Shell size and insert arrangement — for the 1760 primary interface this is fixed at 25-20; state it anyway so an alternate arrangement cannot be substituted.
• Polarization key position — N is the 1760 identification; alternate keys will not intermate with the standard receptacle.
• Contact gender and termination — pin or socket, crimp or solder, and which insert positions are populated. A store may use a subset, but the positions used are fixed.
• Shell finish / class — Class W olive-drab cadmium is the traditional 1760 finish; confirm whether the programme permits a cadmium-free alternative. See our connector plating guide for the corrosion and conductivity trade-offs.
• Lanyard length and fitting — the lanyard is an aircraft-side mechanism; length and end fitting are programme-specific.
• EMI/shielding requirement — 1760 harnesses run alongside high-power aircraft systems. See MIL-DTL-38999 EMI/RFI shielding.
• Qualification evidence — whether the programme requires D38999/31 qualification on the plug, and what evidence is acceptable.

Cross-Reference: 1760 Hardware to Airoadcon

The base connector for the 1760 primary interface is a MIL-DTL-38999 Series III shell — which is exactly the family Airoadcon manufactures as the J599 III series. Cross-referencing therefore proceeds at the configuration level, not the shell level: first match the 38999 part number, then confirm the 1760-specific attributes (shell 25, arrangement 25-20, key N, lanyard release, finish class).

Cross-referencing a 1760 interface is a four-attribute match — shell size, insert arrangement, keying position and finish class — layered on top of the standard 38999 family match. Our complete connector cross-reference guide covers the general methodology; the D38999 part-number breakdown covers the 38999 half of the decode.

Summary

MIL-STD-1760 standardised one interface so that any compliant store can hang on any compliant station — and it did so by configuring an existing mil-spec circular rather than inventing a new one. The 1760 connector is a MIL-DTL-38999 Series III, shell size 25, insert arrangement 25-20 with 30 contacts (10 × #20, 13 × #16, 4 × #12 coax, 3 × #8 twinax), polarization key N, fitted with a lanyard-release mechanism bounded to roughly 90–100 lb of separation force. Around that fixed mechanical core sits the signal set: MIL-STD-704 power, a MIL-STD-1553 dual-redundant bus with 31 usable addresses, high- and low-bandwidth analog, interlock and release-consent discretes, and on Class I stores up to two fibre-optic interfaces — plus, since Revision E, a 1.0625 Gbit/s Fibre Channel channel over the 75 Ω pair.