LoI (level of interoperability)

LoI stands for level of interoperability. It is a formal NATO construct that grades how far a system, most often an unmanned aircraft system (UAS), implements standardised interfaces for data links, command and control, and human-computer interaction. The aim is that different nations' platforms and control stations can work together coherently and efficiently.

In the strict sense, LoI is tied to STANAG 4586 and its implementing publication, Allied Engineering Publication AEP-84. Each numbered level, LOI 1 to LOI 5, specifies a defined set of mandatory messages, interface behaviours and operator functions. The higher the level, the more direct the receipt of sensor data and the more extensive the control over payloads and air vehicles.

The five LoI grades in STANAG 4586

STANAG 4586, titled "Standard Interfaces of UAV Control System (UCS) for NATO UAV Interoperability", defines five levels. They are cumulative, so each level includes the capabilities of the ones below it.

• LOI 1: indirect receipt or transmission of UAV-related payload data.
• LOI 2: direct receipt of intelligence, surveillance and reconnaissance (ISR) or other payload data when the control system has direct communication with the UAV.
• LOI 3: control and monitoring of the UAV payload, in addition to LOI 2.
• LOI 4: control and monitoring of the UAV itself, excluding launch and recovery.
• LOI 5: control and monitoring of the UAV including launch and recovery.

How AEP-84 grades conformance

AEP-84 is a two-volume interface control document that specifies the interfaces in detail. Both volumes are organised around the Data Link Interface (DLI), the Command and Control Interface (CCI) and the Human Computer Interface (HCI). They grade conformance through five levels of interoperability, defined independently for the DLI and the CCI, so a system's level can differ between the two.

Once a set of standards is identified as mandatory for a target LoI, AEP-84 requires it as a whole. A Core UAV Control System (CUCS) or Vehicle Specific Module (VSM) cannot claim a level by implementing only part of the mandatory message set. Conformance means declaring and demonstrating that the mandatory message sets and HCI functions for the stated level are in place.

LoI compared with NATO's force-level interoperability scale

LoI should not be confused with the broader idea of levels of interoperability in NATO doctrine. NATO describes interoperability as the ability for Allies to act together coherently, effectively and efficiently to achieve tactical, operational and strategic objectives. Allied forces assess it on a smaller scale of 0 to 3: not interoperable, deconflicted, compatible and integrated, as explained in a U.S. Army article on multinational interoperability.

That scale describes whole forces. LoI in STANAG 4586 is more granular. It expresses what one unmanned system's interfaces can do, and it focuses on the data exchange and control functions supported.

LoI in Canadian defence policy and tenders

Canadian policy already treats interoperability as a graded objective. The Canadian Army Modernization Strategy recognises de-conflicted, compatible and integrated levels and commits to an integrated level of interoperability with ABCANZ partners by 2027. A 2024 National Defence procurement report states that coalition interoperability is a key consideration in many Canadian Armed Forces procurements. That policy does not use the acronym LoI.

The clearest procurement link is STANAG 4586 itself. A CanadaBuys tender listing includes a Department of National Defence goods item titled "STANAG 4586 COMPLIANT UAV CTRL SYST", opened on 2012-07-24 and closed on 2012-08-08. Because STANAG 4586 defines compliance through a required level of interoperability, a bid against that requirement has to meet a specified LoI.

What LoI means for a supplier bidding on Canadian public contracts

When a Canadian solicitation cites STANAG 4586 or AEP-84, treat the LoI as a technical compliance requirement even if the acronym is not written out. Identify the level the operational concept needs: LOI 2 for direct ISR data, LOI 3 for payload control, LOI 4 for vehicle control, or LOI 5 for full control including launch and recovery.

• Show that your control system implements the mandatory message sets and HCI functions for the stated level, as a whole.
• State the level separately for the data link and command and control interfaces where they differ.
• Describe the architecture, including the CUCS, VSMs and the data link and command and control interfaces.
• Map proprietary data formats and control commands to the standardised messages, and be ready to demonstrate conformance.