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Aero Safety Systems Ah504 Io Expansion Unit

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Part# 11-16245
MFR Model# AH504


The AH504 provides an additional 13 switched and 4 analogue inputs to enhance the number of inputs available in the AH500 and AH502SD warning panels. Connecting over RS232, it provides for more comprehensive alerting, particularly useful for complex aircraft types and where envelope and profile alerts require aircraft configuration data.

Using the AH504 all landing gear limit switches can be monitored in addition to landing and flap position levers. All doors and hatches can be independently monitored and even powered circuits including hydraulic pump, starter motors and air conditioning power can be monitored via the AH-OPTO opto-relays. Additional analogue inputs can monitor temperatures, multiple voltages and current shunts.

The unit measures 5.94in(151mm) by 1.26in(32mm) and has a depth of 0.9in(23mm) as detailed in the Panel Drawing and Installation sheet.
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A configuration file defines the alerts by applying logic to defined states, threshold values or an envelope of flight, engine or aircraft configuration data.

A basic implementation example may include Oil Pressure, Oil Temperature, Low Fuel, Alternator, Starter, Doors and Hatches, Gear unsafe, Voltage and Alternator alerts. These basic alerts can all be generated using directly connected switched and analogue inputs. A simple configuration file maps these to the illuminated captions and voice alerts and consolidates alerts into a Master Warning/ Caution switch.

More advanced alerts can be generated when flight and engine data is added through connection to an EFIS or engine monitor. By combining aircraft configuration data with flight and engine data, Envelopes and Profile alerts can be generated. Examples include recognizing that the landing gear should be down based on airspeed, rate of descent and Height AGL, that oil pressure is too low for the current RPM, that airspeed is outside of the envelope for the current aircraft configuration or that oxygen should be on above a specified altitude.

Careful thought has gone into human factors with auto mute on startup to keep the cockpit quiet when you turn on the master switch and adjustable damping on alert triggers to prevent transitory events causing unnecessary alarms. If your EFIS data feed is off or faulty, the system generates a voice alert to let you know.

The optional AH501 Master/Caution attention-getter / acknowledgement switch helps to draw the pilot’s attention to an anomaly, its switch turns unacknowledged captions to steady and mutes the audio.

Custom legends, voice alerts and basic configuration are all included.

The unit measures 6.25in(159mm) by 1.72in(44mm) and has a panel depth of 1in(25mm) as detailed in the Panel Drawing and Installation sheet.


Why would I need the IO expansion module?
  • To generate intelligent alerts based on aircraft configuration combined with flight and engine data it may be necessary to boost the number of digital and analogue data inputs available in the AH500 and AH502 annunciators. A single legend like ‘Check Doors’ may benefit frommonitoring each door and hatch independently to generate accompanying voice alerts which state which door is unlatched. A check gear alert may benefit from monitoring all limit switches as well as gear selector position in combination with EFIS flight data to generate intelligent alerts. There are many more examples where digital and analogu inputs may exceed the number available in the standard annunciators.
How do I configure the expansion unit?
  • The unit does not need configuration. It feeds data against each input over the RS232 serial data interface directly to the annunciator panel which can reference the AH504 inputs using the XML programmable logic functions.
Can I install it myself?
  • An experienced avionics engineer should be able to easily configure and install the unit. We provide information within this website and provide free of charge support to assist in configuration and installation by telephone and email for installers in the USA and Europe.


  • 13 x protected, filtered and buffered volt-free switched inputs
  • 4 x 0-32Volt, 0.01Volt resolution analogue inputs
  • RS232 interface to connect to AH500 or AH502SD
  • Power 10-32V DC

In The Box

  • AH504 I/O Expansion Unit
  • Installation kit
  • AH504 Installation Manual



Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.