The Safran (Turbomeca) Arriel is built as five modules that can be removed and replaced individually. That is the whole reason module exchanges exist: when one module times out or fails, the operator swaps that module and keeps flying, instead of sending the whole engine away for months. This page explains what each module is, how the numbering works across the Arriel 1 and Arriel 2 families, the hour, cycle and calendar limits on each, and what to check on the paperwork before you commit to an exchange unit.
We stock and exchange these modules. See what is on the shelf: Engine and gearbox exchanges.
The Five Modules Part Numbers and Limits Life-Limited Parts Hours, Cycles, Calendar Log Card Checklist Exchange, Repair, Outright or Lease Which Helicopters FAQ
The Five Modules
The module numbering is the same across the Arriel 1 and Arriel 2 families. Air enters at M02, passes through M03 and M04, and shaft power leaves through M05 at the rear and M01 underneath.
M01 - Transmission Shaft and Accessory Gearbox
Runs along the underside of the engine. The transmission shaft carries drive from the reduction gearbox (M05) at the rear forward to the engine output, and the accessory gearbox at the front drives the fuel pump and control unit, oil pumps, starter-generator and the NG tachometer. It has a 3,600-hour inspection and a 15-year calendar limit for overhaul, but no hour TBO on the Arriel 1; on the Arriel 2 it carries the same TBO as the other modules. Removal for cause is usually accessory-drive related: bearing wear, seal leaks, spline wear.
M02 - Axial Compressor
The single axial compressor stage at the front of the gas path, ahead of the centrifugal compressor. The axial wheel is a life-limited part, so M02 is tracked on NG cycles remaining as well as time remaining to overhaul. Most M02s are removed at TBO; premature removals are typically FOD, erosion from sand and dust operations, or blade damage found at borescope.
M03 - Gas Generator
The centrifugal compressor, annular combustion chamber with the centrifugal fuel injection wheel, and the high-pressure turbine (two stages on the Arriel 1, one stage on the Arriel 2). This is the highest-value module in the engine and carries the most life-limited parts. Premature removals are hot-section findings: HP blade creep beyond limits, borescope findings, performance loss at the power check.
M04 - Power Turbine
The free turbine, mechanically independent of the gas generator. It converts the remaining gas energy into shaft power and drives the reduction gearbox (M05) directly. Its life-limited parts are the free turbine disc (NP cycles) and the free turbine blades (hours and NP cycles). On the 1D1 it is a 7,200-hour module with a mid-life inspection at 3,600 hours. Premature removals are blade creep, vibration and containment-ring or bearing findings.
M05 - Reduction Gearbox
At the rear of the engine. The top connects to the power turbine (M04) and the bottom to the transmission shaft module (M01). It reduces power turbine speed to the output shaft speed and carries the NP speed pickup. On the 1D1 the two main bearings are hour-limited at 7,200. Premature removals are chip detector findings, bearing distress, gear wear and oil seal leaks.
In practice most modules are removed at TBO and returned as cores; the premature cases above are the exception, not the rule.
Module Part Numbers and Limits by Variant
Part numbers you will see on log cards and quotes, with the hour TBO and calendar limit for each module. Where a module has more than one part number the difference is modification state (TU), which matters for interchangeability.
Arriel 1D1 (AS350 B2)
| Module | Part number | TBO | Calendar | Notes |
|---|---|---|---|---|
| M01 Transmission shaft / accessory gearbox | 70BM015420 | on condition | 15 years | 3,600 h inspection |
| M02 Axial compressor | 70BM025020 | 7,200 h | - | mid-life inspection at 3,600 h |
| M03 Gas generator | 70BM035420 | 3,600 h | 15 years | |
| M04 Power turbine | 70BM045410 (post TU) 70BM045400 (pre TU) | 7,200 h | - | mid-life inspection at 3,600 h |
| M05 Reduction gearbox | 70BM055420 | 3,600 h | - | |
| Free wheel shaft | 0292907680 0292907600 | 3,600 h | - | |
| Fuel control unit | several part numbers | 3,600 h | 10 years |
Arriel 2B / 2B1 (AS350 B3, EC130 B4)
| Module | Part number | TBO | Calendar | Notes |
|---|---|---|---|---|
| M01 Transmission shaft / accessory gearbox | 70BM012000 (2B) 70BM010030 (2B1) | 3,500 h | - | the one module that differs between 2B and 2B1 |
| M02 Axial compressor | 70BM022010 | 3,500 h | - | |
| M03 Gas generator | 70BM032030 (post TU 181) 70BM032020 (pre TU 181) 70BM032010 (pre TU 071A) | 3,500 h | 15 years | |
| M04 Power turbine | 70BM041720 | 3,500 h | - | |
| M05 Reduction gearbox | 70BM052000 | 3,500 h | - | |
| Free wheel shaft | 0292907680 0292900200 | 3,500 h | - | |
| HMU | several part numbers, 2B and 2B1 differ | 3,000 h | 10 years |
Arriel 2D (AS350 B3e / H125, EC130 T2 / H130)
| Module | Part number | TBO | Calendar | Notes |
|---|---|---|---|---|
| M01 Transmission shaft / accessory gearbox | 70BM010020 | 5,000 h | - | |
| M02 Axial compressor | 70BM020010 | 5,000 h | - | |
| M03 Gas generator | 70BM030030 | 5,000 h | - | |
| M04 Power turbine | 70BM040020 | 5,000 h | - | |
| M05 Reduction gearbox | 70BM050010 | 5,000 h | - | |
| Free wheel shaft | 0292900200 | 5,000 h | - | |
| HMU | several part numbers | 4,000 h | 10 years |
TBOs move with Safran service bulletins and some operators run under extended or sampled intervals. Treat these as the standard figures and confirm against the current maintenance manual for your engine.
Life-Limited Parts Inside Each Module
The LLPs are why a module can be due long before its TBO. Cycle limits are counted on the gas generator (NG) for the compressor and HP turbine parts, and on the power turbine (NP) for the free turbine parts; the turbine blades carry an hour limit as well. Some LLPs exist in an older and a newer part number with different life limits, so read the part number on the log card, not just the name.
| Module | LLP | Arriel 1D1 | Arriel 2B / 2B1 | Arriel 2D |
|---|---|---|---|---|
| M02 | Axial compressor wheel | 14,000 NG cycles | 22,000 NG cycles | 22,000 NG cycles |
| M03 | Centrifugal impeller | 14,000 NG cycles | 22,000 NG cycles | 22,000 NG cycles |
| M03 | Injection wheel | 10,000 NG cycles (6,500 on older part numbers) | 10,000 NG cycles | 10,000 NG cycles |
| M03 | HP turbine disc | 1st stage 10,000 NG cycles 2nd stage 10,000 NG cycles (6,500 on older part numbers) | 17,000 NG cycles | 17,000 NG cycles |
| M03 | HP turbine blades | 1st stage 12,000 NG cycles / 6,000 h 2nd stage 10,000 NG cycles / 7,200 h | 10,000 NG cycles / 6,000 h | 10,000 NG cycles |
| M04 | Free turbine disc | 10,000 NP cycles | 22,000 NP cycles | 22,000 NP cycles |
| M04 | Free turbine blades | 12,000 NP cycles / 7,200 h | 10,000 NP cycles / 7,000 h | 10,000 NP cycles / 6,000 h |
| M05 | Main bearings | 7,200 h | - | - |
When you read a log card, the remaining life of the shortest of these is the real life of the module. On the 1D1, M02 and M04 also carry a mid-life inspection at 3,600 hours.
Hours, Cycles and Calendar: The Three Limits on a Module
- Hours (TSN / TSO). Time since new and time since overhaul. Each module has its own TBO, set by Safran and subject to change by service bulletin, so the figure on an old log card is not necessarily the current limit.
- Cycles (CSN / CSO). Counted on NG for the compressor and HP turbine parts and on NP for the free turbine parts. Partial cycles count differently from full ones, and the count is only as good as the operator's logging. The LLP with the fewest cycles remaining sets the real life of the module, which can be well short of its TBO.
- Calendar. Some modules carry a calendar limit regardless of hours flown: 15 years on the Arriel 1 M01 and on M03 for most variants. A low-time module that has sat for years can still be due.
What to Check on the Log Card Before You Buy an Exchange
An exchange module is only as good as its paperwork. Before you send a purchase order, read the log card and the release document and confirm:
- Full part number and mod state match your engine and the current IPC. Check every applicable TU (modification) is embodied or that your engine manual allows the configuration.
- TSN, TSO, CSN, CSO are filled in and agree with the release document. A blank cycle count is a red flag.
- LLP status. Each life-limited part listed with cycles used and cycles remaining. The remaining life on the shortest LLP is the real life of the module, not the TBO.
- Release certificate from the overhaul or repair facility, with the work scope (overhaul, repair, inspection, or test only) stated. "Serviceable" alone tells you nothing about what was done.
- Preservation date. Modules in storage are preserved against corrosion for a fixed period and need re-preservation if that lapses. Check the date and whether it was done.
- Reason for removal from the last engine, if stated. A module removed for TBO is a different risk from one removed for a chip detector finding.
- Incident and accident history. Ask. A module from an engine that had a sudden stoppage or overtemp event should have the relevant inspection documented.
If you want a second pair of eyes on a log card before you commit, send it to us. We read these every day.
Exchange, Repair, Outright or Lease
Exchange - you receive a serviceable module now, install it, and send your removed module back as the core. Best when the aircraft is down or you cannot wait out a shop turn time. How our exchanges work.
Repair or overhaul your own - you keep your own module's history, but the aircraft waits for the shop turn, which for an M03 can run months. Best for a planned removal with another engine or a spare module to cover the gap.
Outright purchase - you buy the module and keep your core. Best when the core is scrap, damaged beyond economical repair, or you are building a spare module pool.
Lease - you rent one of our serviceable modules for a defined period, billed per flight hour, and return it at the end of the lease. Best when your own module is in the shop and you want it back rather than a different one. Lease and rental.
Which Helicopters, Which Engines
- AS350 B2 - Arriel 1D1
- AS350 B3 - Arriel 2B (early aircraft), Arriel 2B1 (dual-channel FADEC, most of the fleet)
- AS350 B3e / H125 - Arriel 2D
- EC130 B4 - Arriel 2B1
- EC130 T2 / H130 - Arriel 2D
Modules are not interchangeable between the Arriel 1 and Arriel 2 families, and within a family the variant and mod state matter: the 2B and 2B1 share M02 to M05, the 2D shares nothing with either. If you are unsure what fits, send us the engine data plate and the log cards.
Frequently Asked Questions
Can I Exchange Just One Module?
Yes. That is the point of the modular design. The modules are matched to each other only through standard interface checks and the engine run after installation, not by serial number pairing.
What Is the Difference Between an Arriel 2B and 2B1?
Same core engine; the 2B1 has the dual-channel FADEC and related changes, and most of the AS350 B3 fleet converted to 2B1. M02 through M05 and the free wheel shaft are the same part numbers on both; M01 and the HMU differ.
Does an Exchange Module Change My Engine's Times?
The engine has no TBO of its own; it tracks TSN. Each module carries its own TSN, TSO and cycle counts, and the exchange module brings its own figures with it. Your engine's next scheduled removal is whichever module reaches its limit first.
What Happens to My Old Module?
It is the core. You return it within the agreed window with its log card and release history, and it is inspected against the core standard.
Can You Source a Module You Do Not Have in Stock?
Usually, yes. We have modules in work that are not listed yet, and we source from a network of overhaul shops and operators. Tell us the part number, the date you need it, and the condition of your core.
Reviewed November 2026 by Rotor Parts Network. Figures from Safran maintenance documentation and our exchange records; always confirm against the current manual for your engine.