Buyers ask us a reasonable question: can you put me on a list and tell me when something in my category arrives? It sounds like the efficient way round. On a catalogue that fills the way ours does, waiting to be told is slower than looking — and we can now show why from twelve days of our own counter rather than from an opinion.

This note is about aircraft parts stock updates as they actually happen on a marketplace: not a steady trickle, but batches that land on single days and sit in a narrow corner of the catalogue. Knowing that shape changes how often you look, and where.

Need a part shipped to your region? Submit an RFQ on Aviatrading and reach verified sellers worldwide.

Twelve days of a catalogue counter

We read the total listing count on our own catalogue once a day, from the catalogue’s own pagination metadata, at roughly the same hour each morning. Between 8 and 20 October the readings ran: 3,771, 3,883, 4,046, 4,046, 4,046, 4,049, 4,049, 4,051, 4,051, 4,840, 4,840, 4,840 and 6,410. Thirteen readings, twelve daily changes, all from one source and one method.

Two things stand out in that row. Six of the twelve daily changes were exactly zero. And of the 2,639 listings added across the whole period, 2,359 of them — a shade under ninety per cent — arrived on two days: 789 on 17 October and 1,570 on 20 October.

So the catalogue did not grow by the 220 listings a day the twelve-day average implies. It stood still for most of the fortnight and jumped twice. A buyer who checked on 11, 12, 14, 16, 18 or 19 October saw nothing new at all, and a buyer who checked on the two jump days saw more arrive in a morning than in the whole rest of the period.

Two batches, two different corners of the catalogue

The more useful finding is where each batch landed. We sampled the newest band of 100 listings on each of the two jump days, so each profile below is a measurement on 100 listings out of a batch of 789 and 1,570 respectively — read it as the shape of that band, not as a census of the batch.

The 17 October batch sat in exactly two parent categories: Airframe and Safety and rescue equipment, split 60 to 40 across the band. Every listing on the band carried a fixed-wing platform, and every one carried a single condition code.

The 20 October batch also sat in exactly two parent categories — but not the same two. It was On-board Equipment and Engines, split 74 to 26, again entirely fixed-wing, this time carrying two condition codes rather than one. Neither batch contained a single ground support equipment listing, and neither contained a rotary-wing listing.

On both days the count of named parent categories across the band added up to exactly 100 with nothing left over, which is the check that tells us the profile is complete rather than merely plausible.

Why “nothing new in my category” is not evidence

Put those two profiles side by side and the practical lesson falls out. A buyer watching Airframe would have seen a large arrival on 17 October and nothing on 20 October. A buyer watching Engines would have seen the exact reverse. Each of them, looking only at their own corner, would have concluded on one of those days that the catalogue was static. Both would have been wrong on the same day.

This is what makes a notification a poor instrument here. A per-category alert tells you about your own corner, and the signal it gives you between batches is silence — which is indistinguishable from the silence of a catalogue that is genuinely not moving. Two readings of the whole counter, a few days apart, tell you more than a month of alerts on one leaf.

It also means the honest answer to “when will you have more of this?” is that we do not know in advance, because the arrivals are not paced. What we can say is that two batches in four days went into four different parent categories, so the absence of a thing today carries very little information about next week.

A page number has stopped being an address

There is a trap worth naming for anyone who bookmarks a catalogue position. At a hundred listings to a page, our catalogue ran to 41 pages earlier this month, then 49 after the first batch, and 65 after the second. The content of “page 40” is therefore a different set of listings on each of those three dates.

If you keep a note of where something sat, keep the parent category and the part number, not the page. The two-level address is stable in a way the pagination is not, and we set out how to read it in how a two-level catalogue address works, which also covers what to do when a part number search comes back empty.

One part number, several listings

A batch arrival has one more quirk that is easy to misread. On the newest band we sampled, consecutive listings carried the same part number with different sequence suffixes — one listing per physical unit rather than one listing per part number with a quantity against it.

For a buyer that is good news read correctly: several near-identical results for one part number usually means several units are held, not that the catalogue is duplicating itself. It also means a search that returns a wall of apparently repeated results is worth reading to the end, because the units can differ in condition even where the part number does not.

Condition is the field to check before you compare any two of them. An overhauled unit and a serviceable one are different purchases at the same part number, and the difference is set out in how to read an As Removed parts offer.

What this changes about how you check

None of the above argues for checking more often. It argues for checking differently, and the method is short.

Look at the whole catalogue rather than your leaf, because a batch lands in a corner you are probably not watching. Read the newest page first, since arrivals appear there and a batch is visible in one screen. Compare two total counts a few days apart before you conclude anything about whether inventory is moving — one reading tells you nothing about pace. And when a batch has clearly landed, look across the parent categories it went into rather than only at the leaf you came for, because a 74 to 26 split across two parents is the normal pattern rather than the odd one.

Then stop checking and ask. The reliable way to be told about a specific item is not a category alert but a standing request against a part number, which reaches the people holding stock whether or not it has been listed yet. Everything in the warehouse is not necessarily in the catalogue on any given morning, and the gap between the two is exactly what a request closes.

Where this does not apply

One distinction, because the two questions get mixed up. Everything above is about how somebody else’s catalogue behaves over time and how to read it. It is not about what you should hold on your own shelf, which is a different decision with different inputs — lead time to your station, deferral provisions, shelf life and cost of capital. We worked that one through separately for small operators in building a small fleet spares inventory.

The two do meet at one point, though. If your conclusion from that exercise is that a part is not worth holding, then your cover is a sourcing arrangement, and the quality of that arrangement is what decides how fast you get the part. Watching a catalogue is not an arrangement.

Checking in practice

If you want to see the shape described here, the On-board Equipment hub is where the most recent batch went: browse the on-board equipment listings on Aviatrading and look at how narrow the band of similar items is. For anything specific, submit an rfq with the part number, the platform and the condition you can accept, and let the holders of stock answer rather than waiting for a listing to appear. New arrivals and live requirements are also posted to the Aviatrading Telegram channel, which is the quickest single place to watch for aircraft parts stock updates across categories rather than inside one.