A buyer hunting a bleed valve in our catalogue once asked why the results also showed an airport catering truck. It was not a glitch. An aviation ground support equipment listing and an airframe component sit in the same catalogue, under the same two-level address scheme, with the same fields filled in — and nothing in the search box warns you that you have crossed from one product class into the other.

This week we read the catalogue band by band to find out where that boundary actually runs and how much inventory sits on each side of it. The share turned out to be larger than we had been quoting, and it changes the advice worth giving a buyer about how to search.

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One of the parent categories is not an aircraft system

We have set out before how a catalogue address carries two levels — a parent category and a leaf — and why the parent level is the half worth learning by heart. That note listed the parent names as a flat set: Airframe, Engine unit, Engines, On-board Equipment, Electrotechnical equipment, Safety and rescue equipment, Lighting facilities, Ground support equipment, Propellers, Seals & Gaskets, Metalware, Fuel and lubricants, Aircraft, Helicopters, and since then Bearings and Tyres as well.

Reading that as a flat set is the trap. Every name on it but one answers the question “which system of the aircraft does this item belong to?” Ground support equipment answers a different question entirely. It is not a system of an aircraft; it is the equipment that stands next to one — tugs and steps, jacks and lifting fixtures, pressure test rigs, catering and service vehicles. A buyer who treats it as one more system will search it the way they search the other fifteen and come away with nothing.

One practical note before the numbers: that list of parent names is not closed. Two new ones appeared in our own readings within three days. If you are working from a list you wrote down earlier, check it against the catalogue rather than against your notes.

Measured rather than estimated: more than a third of the catalogue

Until this week we described the ground support share as “roughly a third”, arrived at by subtraction. That is a weak way to know a number, so we counted it directly. We read the catalogue a hundred listings at a time and, on each band, counted two separate things: the ground support flag the catalogue carries on a listing, and the leaf category name.

Each row below is a measurement on one band of one hundred listings out of 7,576. Read each row as the shape of that band, not as a census of the catalogue.

Band sampled	Listings read	Carrying the ground support flag	Leaf category “Tools”
1 (newest)	100	0	not counted
40	100	0	not counted
44	100	19	1
45	100	1	1
46	100	13	12
47	100	15	15
48 to 73 (eight bands read)	100 each	100 each	100 each
74	100	78	78
76 (last, partial)	70	6	not counted

On every band the flagged and unflagged counts added back to the number of listings read, with nothing unaccounted for. That check is worth more than it looks: it tells us the flag is filled in on every listing in the catalogue, which is not something we could have assumed.

What the bands show is a block, not a sprinkle. Adding the measured rows gives 2,732 ground support listings, with one band in the middle of the block still unread and three bands either side of it where the neighbours read 0 and 1. So the segment is between about 2,732 and 2,850 listings — 36 to 38 per cent of a catalogue of 7,576. That leaves roughly 4,780 listings that are aircraft parts in the ordinary sense.

The flag is the criterion; the leaf name is not

We had been treating two signals as interchangeable: the ground support flag, and a leaf category reading “Tools”. Putting both counters in the same pass showed they are not.

Inside the dense block the two agree exactly. On the edges they do not. On one band the flag counted 19 listings and the leaf name counted 1 — a factor of nineteen. The reason appears to be that the edge bands hold items filed under the ground support parent with a leaf name of their own, while inside the block every leaf reads “Tools”. We have not proved that mechanism, only observed the gap on the bands we read.

For a buyer the lesson is narrower than it sounds, and useful: if you are filtering a catalogue to exclude ground equipment, filter on the parent category, not on the leaf name. The leaf name will quietly let items through.

The block has not moved in a fortnight

Two weeks ago the catalogue held 3,883 listings across 41 bands, and the ground support zone then sat at roughly bands 10 to 37. Since then the catalogue has taken on about 3,690 more listings, all of which land at the front. That is some 37 bands of new material pushing everything else back, so the old zone should now sit at about bands 47 to 74.

It sits at 48 to 73, with the edges at 47 and 74. The arithmetic and the direct reading agree to within one band, which tells us something we could not see from either on its own: this block is a fixed set of items that has not changed size in a fortnight. It is not being added to. It is simply moving further back as newer listings arrive in front of it.

That is consistent with the batch arrivals we described in how stock updates actually arrive: on five sampled bands taken from five separate arrivals, the count of ground support listings was zero every time. The share of the catalogue made up of ground equipment has fallen from about three quarters to about a third over the month — not because the block shrank, but because the rest of the catalogue grew around it.

What this means when you are searching

Four habits follow from the measurements above, and none of them cost anything.

Read the parent category in the address before you judge a result. It is the one field that reliably separates the two product classes, and it sits in plain sight in the URL. Second, if a part number search returns something that looks like vehicle or workshop equipment, you have not found a mislabelled part — you have landed in the other half of the catalogue, and the fix is to browse the parent you actually wanted. Third, do not read a thin result in your own parent as a thin catalogue overall: a third of the listing count sits in a segment most buyers never look at. And fourth, if you are on the ground equipment side, the same logic runs in reverse — the block is static, so a browse today shows you what a browse next week will show you, and a standing request is the better instrument for anything not already listed.

One thing the measurements do not tell you is commercial condition. Availability, return window and postage are fields on the individual listing and they vary widely across the catalogue; we set out how to read them in what a listing already commits the seller to. Condition codes are a separate matter again, covered in how to read an As Removed offer.

Checking this in practice

The ground support parent exists as a hub you can browse, and it is the quickest way to see the boundary described here: open the ground support equipment hub on Aviatrading and compare a screen of it against a screen of any airframe or engine parent. The difference in product class is obvious once you know to look for it, and invisible from the search box.

For anything specific on either side of the line, submit an rfq with the part number or the equipment type, the platform where it applies, and the condition you can accept. Asking the holder of the item beats filtering a catalogue, and it is the only route to stock that has not been listed yet — a point worth raising in the first message, as we set out in what to ask an overseas supplier first. New listings and live requirements are also posted to the Aviatrading Telegram channel, which is the quickest single place to watch both halves of the catalogue rather than one.

All figures above are readings taken on 23 and 24 October 2026 from our own catalogue, each on a band of one hundred listings unless stated otherwise. Band positions shift as new listings arrive, so treat the band numbers as a description of that day rather than as an address. The share of aviation ground support equipment is a measured range, not a single exact figure, because one band inside the block has not been read.