Buyer's guide

Buying aircraft filters: element, housing or kit, micron rating, bypass, paperwork and what to put on the RFQ

By the MG AVIATION TECH team · Published · 9 min read

Filter elements are among the most routine lines an airline or MRO buyer places: hydraulic pressure, return and case drain elements, fuel and engine lube elements, IDG filter kits, cabin recirculation filters. They are also easy to get subtly wrong, because a filter assembly is several part numbers, and the one that fits the housing is not automatically the one the aircraft is approved for. This guide covers how filter part numbers are structured, why micron rating and bypass behavior belong to the part number, why elements are nearly always bought new and in quantity, which paperwork to expect, and what to write on the RFQ.

The short answer

  • Element, housing (head and bowl) and kit are separate part numbers. Order the element number your IPC or CMM calls out for the filter position, not the number on the housing.
  • Micron rating and bypass setting are properties of the approved part, not of its size. An element that fits the bowl but filters coarser, or collapses at a lower differential pressure, is a different part.
  • Micron-type elements are consumables. The FAA describes them as normally thrown away when removed; housings, bypass valves and differential pressure indicators are the repairable part of the assembly.
  • Ask for the certificate on every line. In the supplier quotes we received, almost half of filter lines stated none.

Which "aircraft filters" this guide is about

Search for "aircraft oil filter" and the results are almost entirely spin-on filters for piston engines, sold through general aviation retail catalogs with a price on the page. This guide is for the buyer supplying turbine transport and business aircraft: filter elements for hydraulic systems, engine fuel and lubrication, integrated drive generators (IDG) and constant speed drives (CSD), and the air systems of the cabin and equipment bays, bought against an IPC, a CMM or a maintenance task card.

Element, housing, kit: three different part numbers

The FAA's Aviation Maintenance Technician Handbook – Airframe (FAA-H-8083-31B) describes the typical inline hydraulic filter as "three basic units: head assembly, bowl, and element." The head is secured to the structure and lines, and "within the head, there is a bypass valve that routes the hydraulic fluid directly from the inlet to the outlet port if the filter element becomes clogged." The bowl "is the housing that holds the element to the filter head and is removed when element removal is required."

For a buyer, that gives three kinds of line:

  • The element: the part replaced at every filter change, under its own part number. This is the line that repeats on your RFQs.
  • The filter assembly or its sub-parts: head, bowl, bypass valve, differential pressure indicator. These are bought when something is damaged or when a unit is exchanged, not at routine changes.
  • A kit: some manufacturers sell an element with the parts replaced alongside it, or a set of elements for one unit, under a single kit part number. IDG filter kits for the unit's charge and scavenge filtration are one example. Check the kit's contents against the IPC or CMM before you treat the kit number and the separate element numbers as the same order.

The element number is also the one that gets superseded and the one with PMA equivalents. A superseding or alternate number offered in a quote needs the same approval as any other alternate (see alternate and interchangeable part numbers).

Micron rating and bypass: never substitute by size

Two elements can have the same length, diameter and end fittings and still be two different parts. The FAA handbook explains what differs:

  • Micron rating. "The filter rating is given in microns as an indication of the smallest particle size that is filtered out." The handbook's example hydraulic micron element "is designed to prevent the passage of solids greater than 10 microns"; for fuel, it notes that micronic filters on turbine aircraft capture particles "in the range of 10–25 microns." Which rating is right for a position is set by the system designer, not by the element's dimensions.
  • Bypass and differential pressure. In the handbook's example, "the spring-loaded relief valve in the filter head bypasses the fluid after a differential pressure of 50 psi has been built up." A differential pressure indicator on the assembly shows when the element is loaded. An element that does not match what the assembly was designed around can defeat that protection, and the FAA warns that failing to replace a loaded element "can result in system starvation, filter element collapse, or the loss of filtration where bypass assemblies are used."
  • Media type. The element "may be a micron, porous metal, or magnetic type." The micron element, of specially treated paper, "is normally thrown away when removed"; porous metal and magnetic elements "are designed to be cleaned by various methods and replaced in the system."

The handbook's instruction to technicians is short: "Replace the element with one that has the proper rating." For a buyer, that means the rating is carried by the part number, and a size match offered as an alternative is not an alternative until your engineering or approved data says so.

Filter types a transport-aircraft buyer sees

The table summarizes what the sources say about each family and what it means on an RFQ. Replacement intervals are the manufacturer's and your maintenance program's; the figures quoted are the FAA's and GAO's examples, not limits.

SystemWhat you buyWhat the sources sayBuyer note
HydraulicPressure, return and case drain elements; filter modules and their headsFilters sit "in the pressure line, in the return line, and in the pump case drain line of each system." Absent specific instructions, the FAA handbook gives 3,000 h (pressure), 1,500 h (return) and 600 h (case drain) as a recommended element service life.Three elements per system, often three different numbers. After a pump failure the FAA says replacing the system filter elements must be considered, so a pump replacement can bring element lines with it.
FuelEngine fuel filter elements; tank outlet and inlet strainersStrainers are "relatively coarse wire mesh"; filters are fine, and "strainer" and "filter" are "sometimes used interchangeably."A description that says "strainer" may be a filter element and vice versa. Go by the part number.
Engine lubricationOil filter elements, often pressure and scavenge on the same engineFuel and lubrication systems are listed among commercial aircraft filtration applications (Pall).Engine-specific. Quote engine model and the element number from the engine IPC.
IDG / CSDCharge and scavenge filter elements, or a filter kit under one numberCovered by the generator's CMM and the aircraft maintenance program.Say whether you want the kit or the individual elements, and check the kit contents.
Cabin recirculationHEPA recirculation filtersThe FAA: "Most U.S. commercial airplanes use High Efficiency Particulate Air (HEPA) filters in the recirculated airflow, which remove 99.97 percent of particulate material." GAO (2004): the FAA did not require filtration of recirculated air, and airlines typically changed them "after 4,000 to 12,000 hours."Say whether you quote per filter or per aircraft set, and ask for packed dimensions: freight is charged on size as well as weight.

Consumable elements, repairable housings

The split between throwaway and repairable parts drives how filters are bought:

  • Micron-type elements are consumables. They are replaced "periodically according to applicable instructions" and discarded. There is nothing to overhaul, so there is no exchange, no core and no overhauled (OH) stock to speak of. Buyers stock them in quantity against the maintenance program.
  • Housings, heads, bypass valves and indicators are repairable. The FAA handbook notes that differential pressure indicators "are a component part of the filter assembly in which they are installed and are normally tested and overhauled as part of the complete assembly," although on some models the indicator can be replaced on its own. Those lines behave like any other rotable: overhauled or serviceable condition, a maintenance release, sometimes an exchange. See our guide to buying hydraulic pumps and valves for how rotable lines are quoted.
From our quote data

In supplier quotes we received between June and September 2026, lines describing a filter or filter element made up 1,825 priced offer lines for 257 different part numbers. 67% were offered new (NE) and 24% new surplus (NS); overhauled and serviceable together were under 3%. A minimum order was stated on 62% of filter lines.

That profile matches a consumable part, and with a minimum stated on most lines, a unit price is only comparable once you know the minimum. NS elements are unused stock that has passed through other owners (our guide to condition codes explains the difference); for an element, ask how it was stored and whether it is in its original packaging, because a damaged pleat or end seal is not visible from a quote.

Paperwork: 8130-3 or certificate of conformance

A new filter element from the factory may arrive with an FAA Form 8130-3 or with the manufacturer's own shipping documents and certificate of conformance. Both can be legitimate in the US system:

  • Under 14 CFR 21.137(o), a production approval holder has procedures for issuing authorized release documents (the 8130-3) "if the production approval holder intends to issue those documents." It is not obliged to.
  • The FAA's AC 20-62E says documents "such as shipping tickets and invoices may provide evidence that a part was produced by a manufacturer holding an FAA-approved manufacturing process."

What your receiving inspection, your customer or the aircraft's authority accepts is a separate question. An EU-registered aircraft, a lessor's return conditions or your own quality manual may require an 8130-3 or an EASA Form 1 for a new element; our guide to 8130-3 vs EASA Form 1 covers which one you need.

From our quote data

Of the 1,825 filter lines in supplier quotes we received between June and September 2026, an FAA 8130-3 was named on 27% and an EASA Form 1 on 9% (a dual release counts in both). That is about twice as often as for lighting parts (14%) or seals (15%). Still, 46% of filter lines stated no certificate at all, and a trace was stated on 37%.

A blank certificate field does not tell you whether the stock has an 8130-3, a CoC or nothing. Ask on the RFQ, and compare lines only once each names its paperwork.

PMA filter elements

PMA alternatives exist for many filter elements. One public example: a retail catalog lists PTI Technologies' 7588561 hydraulic element as FAA-PMA approved for Boeing 727, 737 and 757 series aircraft, and names Boeing 10-60593-12 as the part it corresponds to. A PMA element can be a sound buy, but it is a decision about approved data, not about fit:

  • Check that your aircraft model is on the PMA's eligibility, in the FAA's records or with the PMA holder.
  • Check whether your operator, customer or lessor accepts PMA parts; not all do.
  • For an aircraft on the EU register, check the extra statement EASA expects on the 8130-3 of a PMA part.

Our guide to PMA parts vs OEM covers the approval routes, eligibility and paperwork in detail. On the RFQ, state line by line whether PMA is acceptable; otherwise you may receive the PMA number as a "direct replacement" with no warning.

Storage and packaging

Whether an element carries a storage limit is set by its manufacturer and your procedures, not by a general rule. Ask for intact original packaging, and for the manufacture date if your quality system tracks it. Elements with elastomer seals fitted raise the same age questions as loose seals; our guide to aircraft parts shelf life explains cure dates and how to ask for remaining life.

What to put on a filter RFQ

A filter line gets a usable answer when it names the position, the paperwork and the policy on alternates. An example:

#Part numberDescriptionQtyCond.Requirements
1[element P/N from IPC]Element, filter, hydraulic, pressure, sys A12NE8130-3 or mfr CoC, state which; no alternates; state MOQ and pack size
2[kit P/N from IPC/CMM]Kit, filter, IDG4NE/NSList kit contents; original packaging; PMA not acceptable
3[filter P/N from IPC]Filter, recirculation, HEPA, shipset2 setsNEQuote per shipset; packed dimensions and weight; certificate named

And a checklist before you send it:

  1. The element or kit number exactly as in the IPC or CMM, not the housing number and not a number read off an old element.
  2. A description that names the system and position (hydraulic pressure, return, case drain; engine fuel; lube scavenge; IDG; recirculation), so a mismatch between number and use is caught before shipment.
  3. Element, assembly or kit: say which. If you need the housing or indicator, say whether overhauled or serviceable is acceptable.
  4. Condition: NE, NS or either.
  5. The certificate you need: manufacturer's CoC, 8130-3, EASA Form 1 or dual release.
  6. Alternates and PMA: none, or the specific numbers you accept.
  7. Quantity against the minimum: ask for the minimum order and pack size per line, so a low unit price is not a large minimum in disguise.
  8. Packaging: original, intact, with part number and lot on the package; the manufacture date if your procedures ask for it.

Carry the same requirements onto the purchase order and check them at receipt. Our guide to where to buy aircraft parts compares OEM distribution, independent suppliers and marketplaces for lines like these.

Send your filter 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 element or kit number exactly as in your IPC and the certificate and PMA requirement on each line. Your inquiry will be reviewed by a specialist within one business day.

Send your RFQ →

In our client portal, RFQ Radar, every quoted line shows its condition, certificates, lead time in days and minimum order, so filter lines can be compared once the paperwork and minimum are on the page. A purchase order there has a "certificate needed" tick on each line and a note.

Before you buy, check what certificates and trace come with each part. Aircraft on ground? See how our 24/7 AOG desk works.

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