Does an air transport protective case always need a relief valve?

Answer: Yes when the routing includes a pressurised hold and the case is closed on the ground. At 55 kPa the lid lifts against the latches.

Is the outer size simply cavity plus wall?

Answer: No. Foam adds 25 to 40 mm and the valve and hinges protrude 8 to 12 mm, either of which can jam the case in a door frame.

How many corners should a drop test cover?

Answer: Three weak bottom corners plus one latch edge and one handle side, rechecking the lid joint each time.

Can a small order skip loaded stack testing?

Answer: No. Only the 24 hour loaded deflection predicts field behaviour, because an empty case is braced by nothing.

How are colour and latch pull judged?

Answer: Colour within Delta E 2, latch pull within plus or minus 10% of nominal on five sampled cases.

Air Transport Protective Case: 5 Selection Criteria

Quick answer: Write the flight profile, derive outer size from the cargo door, match the relief valve to the pressure swing, prove strength at the weakest corner, then make the paperwork agree.

Start With the Flight Segments
Size and Weight Come From the Cargo Door
Pressure Equalisation and Temperature Swing
Drop and Stack Against the Worst Leg
Documents, Markings and Batch Consistency
FAQ

1. Start With the Flight Segments

An air transport protective case is judged by the journey, not the shell. In one day it may be forklifted onto a pallet, wait forty minutes on the apron, fly three hours in a pressurised hold, then be lifted onto a truck.

Crushing and side impact arrive on the ground, temperature extremes and rain on the apron, low pressure and cold in the cruise, a drop at unloading. The quiet legs set the limits, because that is where repair logs cluster.

Leg	Condition	Requirement
Warehouse to pallet	Fork pockets, single lifting	100 mm fork clearance, gravity line on shell
Apron wait	Minus 20 to 55 degrees Celsius, rain	Seals rated both ends, latches cold-tough
Pressurised cruise	About 55 kPa across the wall	Vent path that bleeds air first
Unloading	Drops near 1.2 m, second stack	Corners that absorb energy

2. Size and Weight Come From the Cargo Door

An air transport protective case is sized from the door opening, not the cavity. Narrow-body belly doors sit near 1.2 m by 0.9 m, a wide-body LD3 door closer to 2.6 m by 1.7 m. Keep 50 mm on the long edge and 80 mm in height, or handlers tilt it and loading doubles.

Air Transport Protective Case: tan case open on a warehouse floor, grey foam lid with two recesses, white parcels in foam, empty racks behind

Foam takes 25 to 40 mm and the valve and hinges protrude 8 to 12 mm, so the envelope of an air transport protective case is never cavity plus wall. Above 32 kg crews reach for a forklift, so fork clearance is mandatory. Above 500 kg, straps are rechecked against pallet tie-downs, and a gravity offset past 100 mm doubles the load on one tine.

3. Pressure Equalisation and Temperature Swing

Cruise differential reaches about 55 kPa, so a case closed on the ground is pushed outward at altitude, the seal rolls out of its groove, and it looks latched after landing although it has failed.

Cracking pressure near 4 kPa sits just under the seal force, and 1.2 litres per minute equalises a 50 litre cavity within an hour. Mount the valve high on the wall, not in the lid centre. Silicone holds from minus 20 to 55 degrees Celsius where nitrile stiffens, and groove compression of 25% to 30% keeps contact after contraction.

4. Drop and Stack Against the Worst Leg

Drop testing is about the weakest corner. Unloading usually ends with the case on an edge, so force lands on a corner, a latch edge or the handle side. At 1.2 m, an air transport protective case spreads that energy into two ribs.

Air Transport Protective Case: long tan case closed on pale concrete, a folding handle at centre, three latches along the seam, steel-framed bench behind

Rib spacing beats wall thickness. At 120 mm, corner drop deflection stays under 3 mm; at 180 mm it roughly doubles and the lid joint shifts enough to push the seal out. Three tiers at 80 kg hold 160 kg on the bottom case for 24 hours with deflection under 3 mm, and four latches at 300 N each need a metal keeper insert.

5. Documents, Markings and Batch Consistency

Acceptance turns on whether the documents agree. Outline drawing, resin grade, valve datasheet, drop and stack report and sealing report must carry one model and batch string.

Document	Must show	Common gap
Outline drawing	Outer dimensions, valve protrusion	Cavity only
Material and batch	Resin grade, colour, batch	Family name only
Relief valve	Cracking pressure, flow, position	Model, no figures
Strength report	Drop attitude, stack tiers	Empty-case stack
Sealing report	Method, specimens, verdict	Claim, no report

The air transport protective case passes on batch sampling. Colour deviation stays under Delta E 2; latch pull on five cases per batch must fall inside plus or minus 10% of nominal.

Conclusion

Selecting an air transport protective case is a sequence, not a specification sheet: fix the profile, size from the door, match the valve to the pressure swing, prove strength at the weakest corner, then make the documents agree. Each step can veto the next; skipped steps return as rework. What separates two suppliers is rarely wall thickness, but whether the apron wait and unloading leg were counted in the air transport protective case.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.