I learned a new word recently: Whinge. It’s an old English
word meaning to moan, or to complain fretfully; to whine. When it comes to
certain shelf life issues, I feel an unexplainable urge to engage in whinging.
Shelf life control should be an easy program to manage,
right? Not always. The easy part is when the packaging on a part has a stated
expiration date; these are most easily identified and placed on your shelf life
control program. Most difficulties however, arise from the following:
New parts that have a stated cure date, but no stated expiration date
or shelf life limitation
New parts that really have a shelf life but do not have either a stated
cure date, shelf life, or expiration date, or any other indication of shelf
In service rotables (repaired or overhauled for example) that have
shelf life limitations, but the company stocking these parts is not aware of
We’ll talk more about these, but first an introduction to
A PRIMER: Certain
parts and commodities (I’ll refer to both collectively as ‘parts’) start to
deteriorate or degrade from the moment they are manufactured. Engineers
determine how long a part or commodity can last in storage, and thus the shelf
life. The shelf life is typically expressed either in the length of time of the
shelf life, or with an actual expiration date. The length of time might be
expressed in quarters (a quarter being three months), 20 Quarters for example
(5 years) from the time of manufacture. It’s most easy when there is a plain
expiration date on the packaging. There is another class of part, which
although it does not deteriorate or degrade as discussed, must nonetheless be
periodically tested. These don’t have a literal ‘shelf life’ per se, but
nonetheless must be tracked as are typical shelf life parts to assure none are
Such parts known to contain shelf life include:
Aircraft Main, or APU Batteries.
Parts containing batteries such as Flight Data Recorders, Cockpit Voice
Recorders, life jackets, Survival Equipment, Emergency Path Lighting Packs,
defibrillators, and Emergency Locator Transmitters (ELT’s).
Parts required by FAR’s to be tested periodically such as ATC
Transponders (FAR 91.413).
Certain o-rings, packings, hoses, or components containing such parts.
Certain greases, paints, enamels and sealants.
Pressure vessels, such as oxygen cylinders and fire extinguisher
bottles have mandatory tests that must be performed periodically. Known as
Hydrostatic tests, the period depends on the type of bottle.
Aircraft First Aid kits.
For these parts, you should have a shelf life control
program that accomplishes the following:
For parts in stock you should have a system to track these such that
stock is rotated for First-In, First-Out, and most importantly, that no stock
is issued beyond its date of expiration. Depending on the markings on these
parts, you may need to affix the expiration date on the individual parts, or
some sort of other conspicuous indicator. There are many variations on how you
control this stock, but suffice it to say that the process should be documented
in your Quality System and be in compliance with your chosen quality standard.
For commodities issued to the shop or to Technicians: Your stock room
may issue greases, paint, and sealants to the shop, or for Technician’s use. If
these are shelf life controlled items, operators typically affix their own
expiration date decals to each issued commodity. Its purpose is to assure that
shop employees don’t use the commodity beyond its expiration date. Most
operators have written procedures making it clear that it is the Technician’s
responsibility to assure when using such products, it not beyond it expiration
But wait! I have not yet engaged in the sport of whinging! Thus far, the
aforementioned Primer section was pretty routine for those of us familiar with
shelf life control. Let’s now examine those challenging areas:
ISSUE: New parts that have a stated cure date, but no stated
expiration date or shelf life limitation: Some people see a stated “Cure Date”
on a part’s packaging and assume the part must be shelf life controlled. Not
necessarily. I’ve seen many parts with a stated cure date, but the manufacturer
helped us by also stating “No expiration date”, or some variation of that.
Great, huh? The problem arises when there
really is an expiration date, but there is no indication of that except the
cure date. Here’s a sampling of the reasons I’ve heard for leaving it off:
The part is also used in the commercial world (non-aviation), where
there is not a quality concern with shelf life, so, to standardize packaging,
they leave off the expiration date.
The expiration dates were originally controlled by military specs, and
those specs are no longer being maintained by the government.
The application determines the shelf life.
Exacerbating this is the fact that quite a few end
users/operators will evaluate these parts and establish their own shelf life
limitations. So what’s a person to do with these parts? Your first option is to
call the manufacturer and ask them if any shelf life limitations exist. Your
second option is to call your customer and ask them the same question.
Regardless, you should be able to track the cure dates for the parts, and state
as much to potential customers for them to make up their mind whether they want
to proceed with the purchase. Unfortunately, there is no black and white answer
to this problem, other than to whinge about lack of support from the
BTW, regarding this pesky issue, see “Royboy’s Counsel”
ISSUE: New parts that
really have a shelf life but do not have either a stated cure date, shelf life,
or expiration date, or any other indication of shelf life. Now, this one really
chaps my hide! Typically, you may have a lot of bearings in stock, and a
customer’s auditor asks you why don’t you have the bearings on your shelf life
control program? Imagine, bearings of course don’t have a cure date on them,
and these don’t have any indication either on the packaging or accompanying
paperwork of such limitations. Surprised, you call the manufacturer, and sure enough,
there is shelf life. You’re now heard to raise your incredulous voice and ask
the obvious: Well, why don’t you put it on the packaging? A long list of
self-serving excuses ensues, along with a cryptic faxed document explaining the
shelf life policy. It is based on the bearing’s preservative grease and
packaging. Unless we are blessed with the Spirit of Prophecy, we are simply not
going to know these things! I’m want to whinge some more, but nah...
For rubber products, there is a document published by the Department of Defense
Titled “Rubber Products, Recommended Shelf Life.” If you are pressed for
placing these commodities on a shelf life program, and you can find no credible
information, I’d use this document. It is free!
The following two are not free, but easily available:
Aerospace o-rings and other molded seals. Refer to SAE ARP5316 for recommended
Aerospace bulk hoses and hose assemblies. Consult SAE AS1933 for age control limits
for acceptance of aerospace bulk hoses and hose assemblies.
ISSUE: In service rotables (repaired or overhauled for example)
that have shelf life limitations, but the company stocking these parts is not
aware of the limitations. Here’s where we could help by expanding a little on
parts affected by shelf life.
Anything with batteries in them: If you see a Cockpit Voice Recorder
(CVR) or Flight Data Recorder (FDR) with an installed acoustic beacon, check
the beacon, and you’ll see it has an expiration date on it. The beacon, or
pinger as some call it, sets off an emergency signal when immersed in water; it
runs on batteries, and thus the shelf life. The beacon is usually a cylinder
about 4 inches long by 1.5 inches in diameter on the front of the CVR/FDR. As
stated, the beacon will have an expiration date, and the repair/overhaul shop’s
paperwork will state the same. Life vests, emergency equipment such as that
found in life raft kits, Defibrillators, Emergency Locator Transmitters, Main
Aircraft batteries, APU batteries, and Emergency path lighting packs, all
contain, or are in and of themselves, batteries. A visual inspection of the
part and paperwork will reveal its shelf life.
Parts required by FAR’s to be tested periodically such as Transponders
(FAR 91.413): This is another potential got-cha. Transponders are typical of
parts that must be periodically tested, in this case every 24 months. They must
be tracked as-are shelf life parts to assure none are issued to your customer
expired. The DOT also requires pressure vessels (like oxygen cylinders) to be tested
periodically. For these parts in your serviceable stock, are they on a
By the way, if this topic is new to you, you should be aware
not to confuse this topic with Life-Limited Parts.
Savvy Shelf Life Purchasers: Keen purchasers of shelf life
limited parts usually put a boiler plate statement in their purchase orders
that they will not accept such parts unless 80% of the shelf life remains. So
much for first in, first out! Of course if there’s an AOG, and you’re the only
game in town, and only 20% remains, guess what? But don’t get me started...