Mid-Continent Instr & Avionics Emergency Power Supply

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Part# 11-05540
MFR Model# MD420


Battery Backup System:18VDC, 1.0 Ah, Lead-acid, TSO

The MD420 Emergency Power Supply System is designed to supply emergency power to the Mid-Continent Instrument 4200 and 4300 series attitude indicator when the aircraft main power buss has been de-energized. Additionally, the MD420 will supply emergency lighting power to two additional instruments such as an airspeed and altimeter. During normal aircraft operation, the MD420 will utilize the aircraft main power buss to recharge or maintain existing charge on the System.
California Prop 65 Warning Symbol

WARNING: The product may contain and/or expose you to a chemical(s) or substance(s) which are known to the State of California to cause cancer and/or birth defects or other reproductive harm.


  • Simultaneously provides one primary power output and three lighting power outputs
  • Pitot/Static ports or optional electrical input provides ability to work in automatic mode without pilot intervention
    Arms at beginning of flight
    Activates instantly upon power loss
    Recharges during flight
    Turns off after flight
  • Utilizes sealed lead-acid cells for reliability and cold weather performance
  • Lighting outputs can power LED or incandescent lighting at 5, 14 or 28 VDC
  • Remote, mini-annunciation switch (with automatic dimming) controls test and manual operations
  • Quality Mil-Spec connectors included
  • Field replaceable battery module(s)
  • Designed to operate Mid-Continent Instruments’ standby attitude indicator for one hour after primary power loss
  • Amp-hours of power at 18V: 1.0 Ah
  • Total system weight: 3.2 lbs.
  • Designed and built in Wichita, Kansas, USA
  • One year limited warranty


  • Power Input: 10–32 VDC; 0.25A nominal, 4.0A max (14V) 2.0A max (28V)
  • Power Output: 18 VDC nominal
  • Battery Capacity: 1.0 Ah (0.05C) at 25°C
  • Certification: FAA TSO-C4c and RTCA DO-160E
  • Weight: 3.2 lbs.
  • Mating Connector: 25-pin female D-Sub (MD25F20JVL0 or equivalent), 9-pin female D-Sub (MD9F20JVL0 or equivalent)
  • Annunciator Lighting: LED backlighting, automatic internal dimming
  • Battery Charging: Automatic recharging when main power is present
  • Compatibility: Provides 60 minutes minimum (when fully charged) of backup power to Mid-Continent’s Electric Attitude Indicator Model 4200 or 4300 and lighting power to two additional instruments (5, 14 or 28V)
  • Battery run time will vary depending on total power load for all other installations



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.

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