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Oxygen

ATA Chapter 35 — N720AK Systems Reference

Overview

N720AK is equipped with the Mountain High EDS-4iP pulse-demand oxygen system. A panel-mounted mode switch toggles between pulse-on-demand and constant flow modes.

Components

ComponentPart NumberSupplierNotes
O2 systemEDS-4iPMountain HighPulse on demand
Mode switchPanel mounted
O2 bottleS/N 602-100814Mountain High6×18, 2216 PSI rating
Cannulas

How It Works

Operating Modes

A panel switch selects between:

  • Pulse Mode: Oxygen delivered in pulses synchronized with inhalation. This is normal operation and conserves oxygen significantly compared to constant flow.
  • Constant Flow: Continuous oxygen flow. Use at high altitude or if pulse mode is insufficient (e.g., nasal congestion, very high breathing rate).

This switch also serves as the system on/off — there is no separate emergency oxygen switch. In an emergency, switch to constant flow.

Inspection & Maintenance

Service History

  • 2026-01-12: O2 cylinder (S/N 602-100814) hydro requalification — passed. Operator: Rod Morton, United Fire. (Invoice in Private/Invoices/)
  • 2026-01-16: Mountain High IPR-0157 regulator overhaul — replaced O-rings, seat seals, valve/reg springs, new E-bypass switch per ECO 2022-001, exhaust-port filter replaced with less-restrictive part (09025-0023-43) per MHTSB-2022-01. Valve test passed at 500/1500/2300 PSI. Cylinder torqued to 60 ft-lbs. (Invoice in Private/Invoices/)

Service Bulletin Compliance

  • MHTSB-2022-01 (Emergency Bypass Control Switch Upgrade): Complied 2026-01-16 during IPR overhaul. Exhaust-port filter at EBC switch Port C replaced with less-restrictive part (old: “05”/“F05”/“MB-05”, new: “43”/“S43”/“MBS-43”, P/N 09025-0023-43). Issue: excessive restriction prevented EBC control line from purging in OFF position, causing oxygen to continue flowing.
  • MHTSB-2022-01A (Customer Advisory): Companion letter noting that in some cases the IPR regulator return spring may also need adjustment. N720AK’s IPR was fully overhauled at the same time, addressing this concern.

References