TSO System Explained

For those people whose job specifically involves the management of ULD, the term TSO is probably one with which they are to a certain extent familiar. They probably also know that their ULD should carry something called a TSO plate but beyond that their knowledge on the subject will be very limited. This article will endeavor to throw some light on this important subject.

Any item of aircraft equipment, regardless of whether it is big or small, is required to have some kind of confirmation from the authorities that it meets certain minimum performance standard. Starting at the top, an aircraft itself has what is known as a Type Certificate (TC). The Type Certificate is issued to the manufacturer of the aircraft once the authority is satisfied that the aircraft type has passed all their necessary performance criteria.

The next level of approval is known as a Supplementary Type Certificate (STC). An STC is typically issued for a fairly significant modification or addition to a particular type of aircraft. For instance, the conversion of a passenger to a freighter aircraft will be done by an organization having an approval to issue an STC. STC’s are typically quite specific to a particular aircraft type and not easily usable across different types of aircraft.

Then at the next layer is the Technical Standard Order, or TSO. The TSO system provides a very effective method for manufacturers of different products which may have applications on different aircraft to be able to meet a common performance standard regardless of where the item will be put to use. There are many hundreds of TSO’s issued for different items, some of which may be quite simple and others extremely complicated. Since the TSO system is what is most commonly referenced around ULD, it is this aspect of aircraft certification that is most important to anyone involved in ULD operations.

When it comes to ULD, there are currently 2 TSO’s that are of interest, TSO C90d and TSO C172, with TSO C203 now on the point of being issued by the FAA. The content of any TSO can be easily accessed from the FAA website.

For many TSO’s, and certainly for those related to ULD, the FAA utilizes an external standard to establish the technical requirements, most commonly those created by SAE International. SAE International has a number of committees made up of subject matter experts from airlines, manufacturers, and authorities, and its system for creating standards follows a well-established and transparent procedure. The TSO itself will reference the standard with or without additional commentary, and then will add the formal requirements of the authority including very specific requirements as to how the item shall be marked to indicate that it is approved under a TSO.

It is important to always be aware that, while an item may have received a TSO approval, the manner in which it may be loaded or installed on an aircraft is always subject to the operating instructions of the aircraft itself. In the case of ULD, the weight and balance manuals make reference to TSO C90 when they reference the ULD requirements applicable to the aircraft.

The TSO system can be considered to have a fairly international basis. Apart from the TSO’s issued by the FAA, EASA for Europe issues ETSO’s and China issues CTSO’s and indeed a number of other countries can and do issue their own technical standard orders. Fortunately in most cases and certainly in the case of ULD’s, the FAA and EASA’s TSO’s for ULD are basically mirror images. They are also fortunately widely accepted as acceptable global standards. Furthermore there are arrangements between various countries – known as bilateral agreements – whereby the TSO of one authority is given an approval for use by another country. This process is known as validation.

From time to time TSO’s are also updated. For instance, the most recent TSO applicable to ULD is TSO C 90d, the original TSO C90 having been issued over 30 years ago. While this means that any application made by any manufacturer for an approval for a new design under the TSO C 90 will have to meet the standards established for TSO C 90d, it does not mean that all previous designs, approved under C 90c, C 90b or even C 90a are no longer valid. Indeed, not only can those ULD’s already supplied under the earlier TSO’s continue to be used but they can also continue to be manufactured indefinitely. The requirements of a new TSO e.g. TSO C 90d only applies when new designs are being submitted for approval.

The requirements for the marking to be applied to every item manufactured under a TSO approval are extremely tightly defined by the authorities.


Shown below other requirements for TSO C 90d


a. Mark at least one major component of the ULD permanently and legibly with all the information in 14 CFR § 45.15b. Mark the ULDs in an area clearly visible after the article (orcombination of articles) is loaded with cargo. The marking must include:

(1) The name and address of the manufacturer.

(2) The name, type, part number, or model designation of the article.

(3) The identification of the article in the code system explained in:

(a) In NAS 3610 Rev. 10, Paragraph 1.2.1, for Type 1ULD’s.

(b) In SAE AS 36100 Rev. A, Paragraph 3.5, for Type 2 ULD’s.

(4) The manufacturer’s serial number of the article, with the option to add the date of manufacture.

(5) The applicable TSO number.

(6) The nominal weight of the article in the format:

Weight: ______kg (______lb).

(7) If the article must be installed in a specific direction, the words “FORWARD,”

“AFT,” and “SIDE” must be conspicuously and appropriately placed.

(8) The burning rate determined for the article under paragraph 3.f. of this TSO.

(9) Any limitations or restrictions.

(10) If applicable, mark the expiration date in the format “ EXP YYYY-MM”

(a) Mark the expiration date of a ULD as a limitation.

(b) Mark each component or subassembly, as described in paragraph 4.b. with its expiration date.

Also, mark the following permanently and legibly, with at least the manufacturer’s

name, subassembly or component part number, and the TSO number:

(1) Each component or subassembly that is easily removable (without hand tools), and

(2) Each component or subassembly of the article that you determine may be interchangeable.

NOTE: Subassemblies and components that are extremely difficult to mark (for example lashing lines) may be tagged per 14 CFR § 45.15d.

c. If the article includes a deviation per paragraph 3.g. of this TSO, the deviation should be

identified by the abbreviation “DEV” and marked after the applicable TSO number

In our next edition of the ULD CARE Newsletter, we will continue the discussion on this extremely important subject, talking about some of the more practical aspects of owning and operating TSO approved items.