Buying APU parts and complete APUs: the model on your aircraft, life-limited rotors, LRUs, airframe-side parts, and buy vs exchange vs lease
An RFQ line that says "APU part" can mean a turbine disk whose value is its remaining cycles, a fuel control unit bought like any rotable, an access door that belongs to the airframe, or a complete APU with a shop-visit pack behind it. This guide starts with matching the APU model to the aircraft from the type-certificate data sheets, explains how an APU is approved, sorts its parts into groups with the paperwork each needs, and compares buying, exchanging and leasing a complete unit. A checklist for the RFQ closes it.
Start with the APU model the aircraft actually carries
Many airliner types were certified with more than one APU option, so the aircraft type alone does not tell a seller which part you need. The aircraft's type-certificate data sheet (TCDS) lists the approved options:
| Aircraft | APU models listed | Where it is stated |
|---|---|---|
| Airbus A318, A319, A320, A321 | Garrett AiResearch GTCP 36-300(A); Pratt & Whitney Rzeszow APS 3200; Honeywell 131-9[A]. The combination depends on model and modification (for the A318, the APS 3200 is the production standard from MSN 2686) | EASA TCDS A.064, Issue 62 |
| Boeing 737-100 to -500 (Classic and earlier) | Honeywell GTCP 85-129 or GTCP 36-280 | EASA TCDS IM.A.120, Issue 29 |
| Boeing 737-600 to -900ER (NG) and 737-8, -9 | Honeywell 131-9[B] | EASA TCDS IM.A.120, Issue 29 |
| Airbus A220 (BD-500-1A10, -1A11) | Honeywell 131-9(C) | EASA TCDS IM.A.570, Issue 25 |
| Embraer 170/195 series, Lineage 1000 | Pratt & Whitney Canada APS2300 | Pratt & Whitney product page |
| COMAC C919 | Honeywell HGT750 | Honeywell product page |
Pratt & Whitney calls the APS3200 the Airbus baseline APU for both the A320ceo and A320neo families, and the EASA sheet lists the 131-9[A] as an option on each A320-family model, so A320-family operators run both. The A220, formerly the Bombardier CSeries, carries its own variant, the 131-9(C). Do not assume parts interchange across these models or variants; the APU's part number and dash number matter as much as the model. Put aircraft type, APU model and APU part number on the RFQ line.
How an APU is approved, and why the aircraft paperwork points elsewhere
In the US, the minimum performance standards a gas-turbine APU must meet are in TSO-C77b, dated 20 December 2000; approval follows the generic TSO procedures of 14 CFR Part 21, Subpart O. The FAA's notice says APUs approved under TSO-C77 or -C77a may continue to be made under their original approval, but a major design change requires a new authorization under C77b. The TSO data package includes Instructions for Continued Airworthiness, a model specification and installation data.
TSO-C77b defines two categories. Category 1 APUs are installed where in-flight APU operation is necessary and are usually required for essential installations, for example where the aircraft relies on the APU for backup electrical power in flight. Category 2 APUs are for installations where in-flight operation is not necessary. Both categories are acceptable in a non-essential installation; only Category 1 has been shown to meet all the test and analysis requirements of the TSO's minimum performance standards.
EASA's certification specification for APUs is CS-APU, with the same Category 1 and 2 split. EASA approves APUs through ETSO authorisation, and its FAQ states that for an APU approval a design organisation approval is mandatory.
The TSO does not cover integrating the APU into the aircraft. That is why the Boeing 737 data sheet, in its section for the NG series, names the APU and then says "Limitations: Refer to the APU TCDS / TSO": APU limits sit in the APU's own documents, while the APU compartment, mounts and controls are part of the aircraft certification.
Four kinds of APU part, four sets of paperwork
The FAA's system/component code table puts the APU under code 4900 and splits it into cowling and containment, core engine, fuel and control, start and ignition, bleed air, controls, indicating, exhaust and oil. It also says that generators, alternators and hydraulic pumps that deliver power to aircraft systems are not APU codes. For buying, a different split is more useful:
| Group | Examples | What decides its value | Paperwork to ask for |
|---|---|---|---|
| Life-limited rotors (LLPs) | Compressor impeller or rotor, turbine disks or wheels, turbine shaft | Cycles remaining against the limit for that part number, and records that prove them | Release certificate, back-to-birth records, life-status sheet, non-incident statement |
| Other internal parts | Nozzle segments, combustion chamber, bearings, seals, cases, gearbox parts | Condition, repair data used, OEM or PMA | 8130-3 or EASA Form 1 stating the work done; trace |
| APU LRUs and accessories | Fuel control unit, surge or bleed valve, load control valve, ignition unit, oil cooler, starter, sensors, controller | Condition (OH, SV, NE), modification status, software where there is one | 8130-3 or EASA Form 1; shop teardown report for OH; SB status |
| Airframe-side APU parts | APU access doors, air inlet door and actuator, exhaust duct and muffler, mounts, compartment parts | Correct effectivity for the aircraft and its modifications | Release certificate; look up the P/N in the aircraft's IPC, not the APU's |
The last group is the one most often sent to the wrong seller. Even for aircraft parts and equipment "mounted on or driven by the APU", CS-APU 20(c) treats those outside the declared APU configuration as installation matters, not as part of the APU; doors, ducts and the compartment sit further out still. An APU shop may not stock an access door; a teardown or airframe parts seller may.
APU LLPs: every rotor has a cycle limit
CS-APU 310 requires that "all APU rotors must have limitations" setting the maximum allowable number of start-stop stress cycles (low-cycle fatigue) or hours representative of typical APU usage, where a cycle includes at least starting the APU, running at specific power settings and stopping. CS-APU 30 requires those mandatory replacement times to be published in a separate Airworthiness Limitations section of the Instructions for Continued Airworthiness.
How many LLPs to expect: an IBA analysis of APU leasing (10 October 2025) said the GTCP131-9A and -9B each contain four LLPs rated at about 30,000 cycles, and the APS3200 uses four LLPs with limits of 32,000 to 50,000 cycles. The exact limit belongs to the part number, from the manufacturer's airworthiness limitations, not from a rule of thumb.
Ask for an LLP status sheet: one line per life-limited rotor, each with part number, serial number, time and cycles since new, the life limit and the cycles remaining. LLPs are replaced at different times, so remaining life can differ part by part, and the APU's own hours and cycles do not tell you what is left on each LLP; the sheet does.
Under 14 CFR 43.10, a life-limited part is "any part for which a mandatory replacement limit is specified in the type design, the Instructions for Continued Airworthiness, or the maintenance manual", and whoever removes one from a type-certificated product must control it by one of the methods the rule lists, such as a record-keeping system or a tag showing part number, serial number and current life status. 14 CFR 91.417 requires the owner or operator to keep the current status of life-limited parts of "each airframe, engine, propeller, rotor, and appliance". What a full back-to-birth pack holds and where chains break is in our back-to-birth traceability guide.
A complete APU: buy, exchange or lease
When the unit on wing is removed, there are three ways to put an APU back in its place:
| Option | What you get | What to settle before the PO |
|---|---|---|
| Outright purchase | A serviceable or overhauled APU that you own; your removed unit stays yours to repair or sell | The full pack (below), LLP cycles remaining against your planned utilization, warranty on the shop visit |
| Exchange | A serviceable unit now; your removed unit goes back as the core | Core return deadline, core acceptance criteria, beyond-economical-repair terms and over-and-above charges. See our exchange and core charge guide |
| Lease | A unit for a period, often while yours is in the shop | How time on the unit is charged, the return condition, and who pays if the leased unit fails |
The IBA analysis describes most APU leases as short-term, "covering shop visits or unplanned removals". Whether to repair your own unit or replace it is covered in our repair or replace guide; the APU-specific inputs are the LLP lives left in your unit and the quoted shop-visit workscope.
What the paperwork of a complete APU looks like
A useful pack for a complete APU covers:
- Unit identification: model, APU part number, serial number, the aircraft type it came from.
- Totals: time and cycles since new (TSN, CSN) and since the last shop visit.
- Last shop visit: the date, the facility and the reason it went in.
- LLP sheet: every life-limited rotor, as described above.
- LRU and accessory status at the shop visit, item by item: new, overhauled, repaired, inspected, or no work performed.
- SB and AD status: service bulletins embodied with dates, and a statement on airworthiness directives.
- Release and storage: the release certificate for the unit and, if it has been stored, its preservation status and when that preservation expires.
Check which authority the release was issued under: a release from a third authority is not automatically acceptable for your registry. Confirm it before you order; our 8130-3 vs EASA Form 1 guide covers which release to ask for. Ask also for the shop's full workscope or teardown report rather than a summary, and for the release certificate of the unit, not only of the parts fitted to it. A "no work performed" line on an accessory means its history before that shop visit is what you are relying on.
Condition codes on APU quotes
The usual codes apply, with APU-specific consequences. An AR (as removed) APU or LRU is a core: it needs a shop visit before it can be installed, and its price should reflect the LLP lives and the likely workscope. OH should come with the shop's report of what was replaced. SV or "inspected/tested" means less work was done, which on a complete APU can mean the unit was inspected and tested but not opened. NE and NS are common for small internal parts and seals, rarer for complete units. What each code promises, and the paperwork behind it, is in our condition code guide.
What suppliers write on APU quote lines
In supplier quotes we received between mid-June and mid-September 2026, we looked at a sample: the lines whose description names the APU (APU, GTCP, 131-9, APS3200 or APS2300). Most APU parts are not described that way, so this sample is a lower bound, not a share of APU parts in our quotes. It covered 57 distinct part numbers. 42% of the lines offered overhauled (OH) material, 33% new (NE) and 12% serviceable (SV). FAA 8130-3 was named on 31% of lines and EASA Form 1 on 17%; 43% named no certificate. A trace was stated on 54% of lines. These figures come from what suppliers wrote, matched by text; they are not a review of any documents.
So close to half of these lines said nothing about the release unless the RFQ asked. If the release, the trace or the LLP status matters to you, and for APU parts it does, write it on the line.
Checklist for the RFQ and the purchase order
Write these next to the part number and repeat them on the PO, so a delivery without them is non-conforming.
| Item | APU LLP | LRU or internal part | Complete APU | Airframe-side part |
|---|---|---|---|---|
| Identification | APU model and P/N; LLP P/N | APU model; P/N and dash | Aircraft type; APU model, P/N, required mod standard | Aircraft type, MSN or effectivity; IPC reference |
| Acceptable conditions | NE, SV or OH; say which | NE, OH, SV; say which | OH or SV; AR only as a core | NE, SV, OH; say which |
| Release certificate | 8130-3, EASA Form 1 or dual, per your registry | Same, stating the work done | Same, for the complete unit | Same |
| Life and history | Back-to-birth pack; cycles remaining; minimum [N] cycles | Time since overhaul, if tracked | TSN/CSN, since last shop visit; LLP sheet with minimum cycles remaining | Not usually life-limited |
| Shop records | Repairs listed on the release | Teardown report for OH | Full shop-visit workscope and findings; LRU status list | Repair data if repaired |
| Statements | Non-incident; non-military | As your customer requires | Non-incident for the unit and its LLPs | As required |
| AD / SB status | Required | Required | Required, with dates | Where applicable |
| OEM / PMA | OEM unless your engineering and lease allow otherwise | "OEM only" or "PMA acceptable" | State the parts policy for the shop visit | State it |
| Commercial | Outright | Outright or exchange; core terms | Outright, exchange or lease; core, return and warranty terms; preservation status | Outright |
| Copies before PO | Full pack | Release and report | Full pack, including the LLP sheet | Release |
A PMA clause in a lease can reach the APU: our PMA guide quotes a sample lease clause that bars PMA parts from the engines, the APU and the landing gear. For wording that applies to any part, see our RFQ guide.
Send your APU list as it is
Send your RFQ to [email protected] in the file you already have (Excel, PDF, a scan or the email body, five lines or five hundred), with the aircraft type, APU model and part number, acceptable conditions and the documents you need written next to each line. Your inquiry will be reviewed by a specialist within one business day. In our client portal, RFQ Radar, each quoted line shows condition, certificates and the country it ships from as the supplier stated them, and a purchase order carries a "certificate needed" tick per line and a note where you can list the LLP status and shop records you need. Check the copies against your program and your lessor's terms before you order.
Our client portal, RFQ Radar, keeps every quote, order and invoice in one place.
Before you buy, check what certificates and trace come with each part. Aircraft on ground? See how our 24/7 AOG desk works.
Sources
- Type-Certificate Data Sheet EASA.A.064, Airbus A318, A319, A320, A321, Issue 62 — EASA, 26 June 2026 (section 6, Auxiliary Power Unit, for each model).
- Type-Certificate Data Sheet IM.A.120, Boeing 737, Issue 29 — EASA, 16 December 2025 (section 6, Auxiliary Power Unit, for the Classic, NG and MAX sections).
- Type-Certificate Data Sheet IM.A.570, BD-500 (A220), Issue 25 — EASA, 21 August 2026 (Auxiliary Power Unit).
- Commercial Auxiliary Power Units — Pratt & Whitney (APS3200, APS2300 applications).
- APS3200 Auxiliary Power Unit, Fast Facts — Pratt & Whitney, May 2022.
- 131 Series Auxiliary Power Units — Honeywell Aerospace.
- HGT750 Auxiliary Power Unit — Honeywell Aerospace.
- TSO-C77b, Gas Turbine Auxiliary Power Units, notice of availability — Federal Register, 66 FR 6753, 22 January 2001.
- Auxiliary Power Units (APU) Approvals, with the subpages APU TSO Approval Minimum Qualification Standards, Data Required by TSO C77b and Category 1 and Category 2 APU — FAA.
- Easy Access Rules for Auxiliary Power Units (CS-APU) — EASA, February 2018 (CS-APU 10, 20, 30, 150, 310).
- ETSO authorisations, FAQ — EASA.
- Joint Aircraft System/Component Code Table and Definitions — FAA, last updated 27 October 2008 (code 4900).
- 14 CFR 43.10, Disposition of life-limited aircraft parts — eCFR.
- 14 CFR 91.417, Maintenance records — eCFR.
- APU leasing shows stable demand and untapped potential in a mature market — IBA, 10 October 2025.
- MG AVIATION TECH — priced offer lines from supplier quotes received between mid-June and mid-September 2026 whose description names the APU, aggregated on 24 September 2026; no prices or supplier names published.