Airfield Lighting Control and Monitoring System (ALCMS)

Definition

An airfield lighting control and monitoring system (ALCMS) is a computer system that controls airfield lights and reports their status.

The FAA names it the airport lighting control and monitoring system and specifies it as the L-890 system. AC 150/5340-30J uses the acronym for both names. AC 150/5345-56B says that the ALCMS simplifies the control and monitoring of lighted visual aids. Its basic function is the same at a general aviation airport with a few operations a day and at a large airport with hundreds.

The airfield lighting control page covers the function: intensity steps, relay panels, pilot-controlled lighting and stop bars. This page covers the system that does it with computers, and what the FAA specification asks of that system.

Parts of an ALCMS

AC 150/5345-56B 3.2 names the major components.

Component	What it does
ATC human machine interface (HMI)	A touchscreen in the tower that shows an airport graphic with buttons for the lights
ATC computer	Receives the HMI commands and sends them to the vault by fiber optic cable, wireless network or copper wire
Remote HMI and remote computer	Show status at other sites, for example operations. They default to view only, and can control if the airport wants it
Electrical vault HMI	Gives an operator interface at the vault. It defaults to view only
Electrical vault computer	Sits in the vault and connects to the vault network
Control and monitoring equipment	Connects the vault network to the constant current regulator (CCR), the circuit selector switch, the generator and other equipment
Vault communications network	Links the vault computer with the controlled equipment. It is dedicated to the ALCMS
ALCMS communications network	Ties the computers together by hardwire, fiber optic cable or wireless. The AC says to use it only for the ALCMS

Two computers can run at the same time for redundancy. The AC does not allow laptop computers as ATC or vault computers.

What an ALCMS connects to

AC 150/5345-56B Figure 1 shows the interfaces. Solid lines are the minimum interfaces of a basic system. Broken lines are options for the airport. The figure shows these connections:

navaid lighting systems, such as ALSF, PAPI , VASI and REIL
runway guard lights
stop bars and sensors of a SMGCS
runway visual range (RVR)
the rotating beacon and obstruction lights
the L-854 radio controller
commercial and standby power

Control rules

The AC sets minimum control requirements (5.1 and 5.2):

The ALCMS controls each lighting circuit element on its own. This includes the brightness steps and on and off.
Control can move between the ATC, remote and vault HMI stations.
The airport can choose exclusive control, with one station in control, or cumulative control, with several.
The airport can enable or disable control at each station, to keep unauthorized places from controlling the lights.
An external interface must not control the lights automatically without confirmation from an HMI. This covers RVR, radio control, photocells and sunrise and sunset tables.

The ALCMS must still provide for a photocell or an air-to-ground radio, and it can show sunrise and sunset notifications at the ATC HMI.

Monitoring types

AC 150/5345-56B Table 1 groups ALCMS by a monitoring type, A to D, and a failsafe type. The designer picks the monitoring type to match the category of operations of the airport.

Type	Name	What it monitors	Typical use in the AC
A	Control only	Computer malfunction, communication link, failsafe state, vault interface failure. No feedback from controlled elements	The AC names no category
B	Basic monitoring	Type A, plus feedback that a circuit is on or off	VFR and Category I
C	Advanced monitoring	Type B, plus burnt-out lamps, regulator current and voltage	Category II and III
D	SMGCS ready	Type C, plus individual lamps out, with location and fixture ID	Category III with a SMGCS plan

Type B proves the on and off state with a current sensing relay or a current transducer on the regulator output. As an example, the AC sets a relay to detect more than 2.5 A on a 5-step regulator. For a 3-step regulator the value is more than 4.5 A. Type C has configurable lamp-out thresholds from 1 to 15 lamps, for a warning and for an alarm. It also reads the true RMS output current and voltage of the regulator, to ±3 percent.

Failsafe

Failsafe is the action that the ALCMS takes when it cannot execute a command for a controllable element. The AC defines two types (7.1):

Type A, preset. The controlled devices go to a pre-defined state, either on at a set brightness or off. The operator can configure the preset.
Type B, last state. The devices stay at the brightness they had before the failure. A device that was off stays off. The device keeps this state even after a complete loss of power, battery backup included. Software must not hold the state.

Airfield lights for Category II and III operations must have the Type B failsafe. For both types, local staff must be able to override the failsafe state at the regulator. The lights stay in the failsafe state while the regulator has primary power.

Events, warnings and alarms

Every event, warning and alarm has a date and time stamp to the second. The AC defines three classes (7.2):

Event. An operator command or a change in the status of monitored equipment. The system logs it.
Warning. A fault or low-level failure that did not yet degrade the visual aids below the serviceability criteria. Warnings show at maintenance interfaces and are filtered from the ATC HMI.
Alarm. A fault that degrades the visual aids below the serviceability criteria. Alarms show at maintenance and at the ATC HMI.

Examples of alarms are:

the protective shutdown of a regulator
a controlled element that does not respond to a commanded step
a lamp-out count at the alarm threshold
the loss of all communication links

The airport sets the storage time of the event log from 1 day to 1 year (7.4).

ICAO and EASA monitoring rules

ICAO and EASA do not use the term ALCMS. They ask for monitoring of the lighting systems.

A system of monitoring should show the operational status of the lights (Annex 14, 8.3.1, and CS ADR-DSN.S.890(a)).
Lighting systems that control aircraft must be monitored automatically, and the fault information must go automatically to the air traffic services unit. This is a Standard in Annex 14, 8.3.2. EASA writes it as “should” in S.890(b).
A change in the status of a light should show within two seconds for a stop bar at a runway-holding position. For all other visual aids the limit is five seconds (8.3.3, S.890(c)).
For a runway for runway visual range below 550 m, automatic monitoring should show a fall below the minimum serviceability level. It should send the information to the maintenance crew and to the air traffic services unit (8.3.4, 8.3.5, S.890(d) and (e)).

The competent authority sets the minimum serviceability level below which operations should not continue (GM1 ADR-DSN.S.890). See remote monitoring for the tower indication rule.

Response times

AC 150/5340-30J, Appendix F, F.4.1, gives the ALCMS response times. The values apply to the lab certification test with a small set of components. They cover the ALCMS only, and not the equipment that it controls. The designer must set timing budgets for the whole system at each interface. The airfield lighting control page lists the values.

What it means on an airfield

An ALCMS reports what the circuit does. It does not report what the pilot sees. Type B shows that current flows. Type C counts lamps out and reads regulator current and voltage. Type D locates each lamp that is out. None of these gives the intensity, the beam spread or the orientation of a light.

EASA asks for that measurement separately. For a Category II or III precision approach runway, AMC1 ADR.OPS.C.015(b) and (f) asks for in-field measurement. It covers the intensity, beam spread and orientation of the approach and runway lights. It asks for measurement at least twice a year for in-pavement lights and at least once a year for other lights.

Check the type. Find out which monitoring and failsafe type the installed ALCMS has. It sets what the alarms can show.
Check the failsafe. Test that the failsafe state matches the preset or last-state design, and that the local override works.
Keep the log. The event log is the record of brightness changes and alarms. The AC lets the airport keep it for up to a year.
Measure the lights separately. Use in-field measurement or an inspection of the lights themselves.

TarmacView’s drone airport inspection checks the lights themselves. It does not replace the ALCMS.

Frequently Asked Questions

What is an airfield ground lighting control and monitoring system?

It is a computer system that controls airfield ground lights and reports their status to the operator. The FAA calls it the airport lighting control and monitoring system and specifies it as the L-890 system in AC 150/5345-56B. The tower, the electrical vault and other sites connect to one network.

What is the difference between an ALCMS and airfield lighting control?

Airfield lighting control is the function of switching lights and setting their brightness. An ALCMS is one way to do it, with computers, touchscreens and a network. Relay panels, multiplexers and PLC systems are other ways. The ALCMS also monitors the status of the circuits.

What does L-890 mean?

L-890 is the FAA specification number of the airport lighting control and monitoring system. AC 150/5345-56B sets the minimum requirements. It is mandatory for projects that receive federal airport grant money. The AC says that an installed ALCMS need not be replaced when the AC changes.

What are the monitoring types of an ALCMS?

AC 150/5345-56B defines four types. Type A is control only. Type B gives on and off feedback. Type C adds lamp-out counts and regulator current and voltage. Type D gives individual lamp-out monitoring and is called SMGCS ready. The AC links B to VFR or Category I, C to Category II and III, and D to Category III with a SMGCS plan.

What happens to the lights if the ALCMS fails?

The lights go to the failsafe state. With a preset failsafe, they go to a pre-set brightness or off. With a last-state failsafe, they stay at the brightness they had. Airfield lights for Category II and III operations must have the last-state type. The AC asks for a local override at the regulator.

Does an ALCMS show each lamp that fails?

Only from Type C and D up. Type C counts burnt-out lamps and gives a warning and an alarm at set thresholds, from 1 to 15 lamps. Type D gives the location and the fixture ID of each burnt-out lamp. Types A and B do not monitor lamps. None of the types measures the intensity of a light at the lamp.

Can radio control or RVR change the lights automatically?

Not without an operator. AC 150/5345-56B says that the ALCMS must not let an external interface control the lights automatically without confirmation from an HMI. The AC lists runway visual range, radio control, photocells and sunrise and sunset tables. The ALCMS must still provide for a photocell or air-to-ground radio.

How quickly must an ALCMS show a change in the status of a light?

ICAO and EASA recommend an indication within two seconds for a stop bar at a runway-holding position. For all other visual aids they recommend five seconds. ICAO Annex 14 8.3.3 and CS ADR-DSN.S.890(c) say this.

This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.

What is an Airfield Lighting Control and Monitoring System (ALCMS)?