How Should a Part 135 or 121 Operator Manage Aircraft Parts Inventory and Purchase Orders to Avoid AOG Delays?

Part 135 and 121 operators avoid AOG delays by tracking rotable and consumable parts against real removal history, setting reorder points tied to MEL and AD/SB deadlines, and pre-clearing the purchase-order approval chain before a shortage happens rather than after a tail is grounded. The goal is to turn parts management from a reactive scramble into a scheduled, auditable process tied to your maintenance program.

Aircraft-on-ground events are rarely caused by a single missing part so much as by inventory and purchasing processes that can't see a shortage coming until it's urgent. A rotable that takes three weeks to source, a purchase order sitting in someone's inbox, or a deferred MEL item nobody re-checked all end the same way: a grounded tail and lost revenue. Getting ahead of AOG risk means connecting parts inventory, purchase orders, and your maintenance program into one visible workflow instead of three disconnected systems that only talk to each other after something breaks.

Why the answer is what it is

Track rotables and consumables against real demand, not a static list

Set min/max stock levels per part number based on actual removal rates, not a list someone built years ago and never revisited. Rotable components like starters, generators, and hydraulic pumps need different reorder logic than consumables like filters, gaskets, and o-rings, because lead times and repair-vs-replace decisions differ.

Tie reorder points to your MEL and AD/SB schedule, not just stock counts

A part sitting at an "acceptable" quantity can still cause an AOG if it's tied to an AD with a hard compliance date or an MEL item nearing the end of its repair interval. Cross-reference upcoming AD/SB deadlines and MEL deferral windows against on-hand inventory so a shortage surfaces weeks ahead, not the day compliance is due.

Standardize the PO approval chain before you need it

Define who can approve an emergency AOG purchase order and at what dollar threshold before a tail is actually grounded — hunting for an approver mid-AOG costs hours you don't have. Pre-clear a shortlist of vendors and repair stations for your highest-risk part numbers so sourcing starts the moment a shortage is flagged.

Rank AOG risk by aircraft, not just by part number

The same part shortage means something different on a spare airframe than on the only aircraft flying tomorrow's charter or scheduled leg. Weigh open parts needs against what each tail has coming up on the schedule so the next purchase order you cut is the one that actually protects revenue.

Keep work orders, parts, and purchase orders in one system of record

When work orders, parts inventory, and POs live in separate spreadsheets or disconnected tools, nobody sees the full picture until the AOG call comes in. Connecting them means a work order that needs a part shows what's on hand, what's already on order, and when it's expected, in one place.

What to look for

  • Set min/max reorder points per part number using actual removal history, not guesswork
  • Cross-check upcoming AD/SB compliance dates against on-hand inventory on a fixed schedule
  • Pre-clear emergency AOG vendors and repair stations before a shortage forces the search
  • Define PO approval authority and dollar thresholds in writing, before you need them
  • Log every MEL deferral with its repair interval and a recheck date, not just a one-time note
  • Rank open parts needs by which aircraft they affect and what's on that tail's schedule
  • Review AOG-risk exposure on a regular cadence, not only after a tail is already down

Related questions

What's the difference between a rotable and a consumable in aircraft parts inventory?

A rotable is a part that gets repaired and reinstalled rather than discarded, like a starter, generator, or hydraulic pump, so it needs a repair-and-exchange process tracked alongside basic inventory counts. A consumable, like a filter, gasket, or seal, gets used once and simply reordered, but its reorder point still has to account for supplier lead time.

How far in advance should an operator reorder AOG-risk parts?

There's no single universal number; it depends on the part's historical lead time, the aircraft's utilization, and whether it's tied to an AD or MEL deadline. A safer approach than a fixed calendar interval is a calculated reorder point: average lead time plus a buffer for likely supplier delay.

Can software predict which parts are likely to cause an AOG delay?

AviationAlley's maintenance module is built to connect work orders, parts and POs, MEL deferrals, and AD/SB tracking with a predictive 0-100 AOG-risk score where every point traces to a named factor rather than a black-box guess. It runs on a deterministic rules engine, not AI, so the same inputs produce the same score every time. AviationAlley is pre-launch software built for this workflow, not an in-market product with a track record yet.

How Roffik addresses this

The platform for FAA-approved Part 142 training centers — simulator scheduling, FAA compliance records, client-account billing, and SWIFT wire reconciliation. Learn more about AviationAlley.

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