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I don't need spares - I have a five-year warranty

Updated: Aug 17, 2023


Between us at Sim Ops, we have heard this statement stated regularly over the years. Having had a conversation predicated on this thought recently we thought we would look at this approach and at spares in general. Oh and spoiler alert, not buying spares is what could be called a brave decision.

What types of spares are we talking about?

Before we look at the possible spares policies let’s look at some definitions, rather than just thinking of a spares package it helps to categorise them, as always there are different ways to do this but we like these definitions;

  • Rotable Parts - these are normally sub-assemblies that have an identity of their own (part number/serial number) and if they fail can, in normal circumstances, be repaired. For example a projector. If one of these fails you are going to look to get it repaired.

  • Non-rotable Parts - again these are again sub-assemblies with their own identities but are not normally repairable. Examples of these would be power supplies, ethernet cards etc where the cost of attempting repair could exceed the value/cost of a replacement.

  • Consumables - these items are fitted to/in sub-assemblies and are not repairable, to use the jargon, lose their identity once fitted. Items in this category are lamps, fuses, grease, oil etc.

  • Aircraft Parts - Parts that are used on the FSTD as aircraft.

For those readers with a NATO military background think A, B and C class.

So, why do you need spares?

Of course, the main reason is to minimise downtime. Having spares readily available is, in the event of a failure, to get the FSTD back in training in the shortest time possible. Yes, if your FSTD is under warranty you will probably, eventually, be sent a replacement part but how long will it take? Are you willing and able to wait three or more days? But it is not even certain you will get a replacement part. If the part that has failed is a rotable part the TDM may elect to repair the item (a lot of purchase contracts we have seen give the TDM the option to replace or repair at their, sole, discretion), in that case can you afford to be without a part for three months? Oh, and remember those consumable parts, all the contracts we’ve seen in recent times exclude these from the warranty.

So the most immediate reason is to minimise downtime; of course, if losing weeks of training time is acceptable to your organisation...

So why else?

There is a secondary reason why you should consider sparing some parts, that is the industry's nemesis, obsolescence. With the increasing use of Commercial Off The Shelf (COTS) parts we have seen real problems with obsolescence. We’ve talked about obsolescence before (Managing Flight Simulation Training Device Obsolescence) and our advice is always to have a policy, one such policy for mitigating the issue is to buy spares while they are available. An additional benefit is spares purchased at FSTD procurement time should have the same revision level as those fitted to the FSTD.

But surely the TDMs can ship any part I need in a matter of hours?

Oh if only! Just think of a large TDM who has been building FSTDs for, say, 40 years (I can think of several). Now think of how many FFS product types they have delivered and how many aircraft types with unique hardware requirements. How many interface board types, host computers, ARINC boards, sound cards, motion systems etc have been used over the years? Between us at Sim Ops we have worked for/with most of these companies and none of them have massive warehouses containing every part ever required, far from it; and that is not a criticism just a reality. Even if they have the part, getting it to you is not always as quick as you might like, whenever parts are subject to customs clearance the shipping times are out of their hands.

OK, so what spares should I buy, how much will it cost?

The best time to buy spares is always at the time you’re buying your FSTD; if you package the parts into the purchase for one thing you will be in the best position to get a good deal. This is also the best time to ensure that all the parts you need are available, back to our obsolescence issue.

Which spares you need is where you need help. The TDM should provide you with a recommended spares list or possibly a “Critical Spares” and “Recommended Spares List”. If the product you are buying has been in production for a while these lists will hopefully be based on in-service data. If a new product, they will be based on their experience of similar products. Sadly a lot of spares packages are chosen to fit within a defined budget. To break this we advocate returning to what used to be common practice, but today seems to have fallen out of fashion, that is the “Spares Conference”. Go to the TDM’s factory and spend 1 or 2 days going through the list line by line and then go to the device and check what is on the list; if you have a cantankerous seasoned simulator technician, send them.

How much to spend? That’s where it becomes problematic. During the RFQ stage the competing TDMs will be very aware that the cost of spares will be added to the FSTD price along with all selected options to come up with a total cost of acquisition (in fact you should be looking at the total cost of ownership but that is more complicated and a topic for another day). Hence if they provide a conservative price it makes their overall price more attractive. For the acquirer it’s again a good thing for the budget at the time of purchase, but a spares list missing critical albeit expensive parts may lead to serious problems down the road.

What else can you do?

For the spares contents the best advice we can give is to request from the TDM, before the contract is signed, to put a requirement into the warranty clause whereby if, during warranty, a part fails that was not recommended the TDM not only supplies a replacement for the failed item but an additional spare as well (they either have confidence in their spares list or they don’t, if they refuse this they probably don’t).

We would also recommend buyers put a clause in the purchase contract obliging the TDM to supply a one-year package of consumables with the device; this is not about costs but to give you time to establish supply sources that don’t rely on the TDM (OK it is also a little to do with costs).

For Aircraft parts there is good(ish) news; in most current devices there are very few actual aircraft parts used as most are fabricated and simulated to a high standard by the TDM. For those remaining, although expensive, they can be often sourced through the same specialist companies that airlines use. That said some of the aircraft manufacturers through their simulation packages are pushing in the opposite direction.

Other Spares Services available

Some of the TDMs also offer spares services including Consignments, Depot Stocks and Availability Guarantees backed by Service Level Agreements. These can be a way to mitigate problems but bring with them their own issues, we’ll look at these in a future blog.


So in conclusion, yes you need spares, it can be seen that the process of sparing for an FSTD is by no means something to be dismissed lightly. The long-term effect on training and upfront cost has to be balanced. There is no one ideal solution as every training centre has a different approach to how they want to operate. But the person who advocates having no spares on site and needing to achieve a high availability is an extremely brave person.

How can Sim Ops Help?

Every FSTD operator has different specific requirements for their business model for FSTD and/or training centre operation. Sim Ops are your ideal partner to help you through the process of defining your spares holdings and to explain the many advantages and disadvantages of each of the service offerings proposed by the TDMs. And if you need a cantankerous seasoned simulator technician let us know.

Our staff have lifelong experience in the procurement and in-service usage of spare parts and spares services.

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