Can a ground support case go onto the bridge?

Answer: It passes but cannot stop there: the bridge is 1.4 m wide against a 550 mm shell, and the moving end reaches 3°, where 20 kg needs 10 N or it rolls.

Why colour blocks instead of numbers?

Answer: A numeral needs reading at 200 mm under 50 lx, where half a glove makes it worse. A colour block works on hue over area, red and grey three times apart.

Are 12 compartments enough?

Answer: At nine turnarounds and six items each, 12 is two turnarounds of stock. Under nine, a second pick reopens a closed ground support case; over 15, the shell passes 600 mm and the bridge gap falls under 200 mm.

Does 55 °C apron heat deform the shell?

Answer: The 1.5 mm sag and 0.8 mm offset are elastic, returning inside 0.2 mm once cooled. Long parking is worse: six hours in sun takes the interior to 72 °C and the seal to 8% compression set.

Why not build it as a trolley case?

Answer: A handle lifts the centre of gravity 200 mm and drops the tipping threshold from 1.53 g to 0.72 g, and claims 40 mm of length 12 compartments cannot spare.

Airport Ground Support Case

Quick answer: A ground support case opens in 3 s, spends 8 s per item and tows 300 m back, using 5.5 of the 25 minutes a narrowbody turnaround allows.

Where a Ground Support Case Sits in a 25 Minute Turnaround
Three Seconds to Open: Two Latches and a 105° Lid
Twelve Compartments and Four Colour Codes
Finding the Right Slot With Gloves On
The 300 m Tow and 75 mm Castors
FAQ

1. Where a Ground Support Case Sits in a 25 Minute Turnaround

A narrowbody turnaround runs 25 minutes: 2 for the bridge, 8 for disembarking, 6 for cleaning, 5 for catering and fuelling, 3 for pushback, 1 buffer. The ground support case takes three gaps inside that block, each ending with the lid shut behind the yellow line.

Nine turnarounds per shift means nine openings, so each gets 6 minutes: 3 s to open, six items at 8 s, 3 s to close, 4.6 minutes to tow 300 m, 5.5 minutes in total.

Turnaround stage	Duration min	Pick and place action
Bridge on	2	Two-person lift, lid open in 3 s
Disembarking	8	Red slots, 3 compartments, 8 s per item
Cabin cleaning	6	Yellow slots, lid shut, shifted 2 m
Catering and fuelling	5	Blue slots, grey left untouched
Bridge off	3	Lid down, latches closed, 300 m tow

Timing pressure sits in closing: a shell at the door obstructs the bridge once it moves, so the 12 compartments are ordered backwards from that countdown.

2. Three Seconds to Open: Two Latches and a 105° Lid

Three seconds is three movements: 0.6 s on a latch, 1.4 s to lift, 1 s for the stay. Every extra latch costs 0.6 s, so a four-latch shell spends 2.4 s on latches alone. This ground support case carries two, 150 mm either side of centre.

Ground support case foam inserts stacked on a green floor, each block cut with rectangular compartments and one full-length slot

The 105° stop lets the lid hold itself: past the balance line both hands are free, while 90° falls back 15° and 120° fouls the handrail. A cold seal stiffens until opening force climbs from 40 N to 64 N, and the lid needs 4.8 s at -10 °C.

Surface temperature °C	Opening force N	Opening time s
-10	64	4.8
20	40	3.0
40	41	3.1
55	44	3.3

Heat causes a shape problem instead: at 55 °C the 550 mm lid sags 1.5 mm and the latch sits 0.8 mm off its keeper.

3. Twelve Compartments and Four Colour Codes

Twelve compartments sit in three rows of four, each 110×90×80 mm with 8 mm walls, filling a 520×370 mm plan. They are not equal: the two columns nearest the handle are 80 mm deep and the two nearest the hinge 60 mm, because fingers enter at a sharper angle.

Four colours run red, yellow, blue and grey on the front wall of each compartment at 15 mm, never on the floor or in the lid. A floor stripe hides while the lid is shut and a lid stripe has to be opened first; the front wall shows at 30° and a sweep across 12 compartments takes 1.2 s.

Colour code	Compartments	When it is used	Pick time s
Red	3	Disembarking, first out	8
Yellow	3	Cabin cleaning	8
Blue	3	Catering and fuelling	8
Grey	3	Spares, never opened mid-turn	0

Colour follows frequency, not size. The red three open on all nine turnarounds and the grey three once in nine, so the ground support case puts the frequent group 120 mm from the fingers.

4. Finding the Right Slot With Gloves On

Apron floodlights on 12 m masts give 50 lx, and the working plane about eight tenths of that. A 15 mm block subtends 2.9° at 300 mm, enough to separate red from grey but not to read a 3 mm numeral, so the compartments carry no numbers.

Ground support case shells on a shrink-wrapped pallet, three black lids lying on top, green floor and packing line behind

Colour solves seeing; shape solves feeling. A 1.2 mm winter glove lifts the touch threshold from 0.1 mm to 0.4 mm, so the four zones differ in opening width instead: 110, 106, 102 and 98 mm, 4 mm apart, felt as a finger crosses the slot.

What decides the 8 s is the path: 2 s to reach, 3 s to draw, 3 s to return. The return leaks time with a wet glove, and a 2 mm concave floor centres the item to 2.2 s.

5. The 300 m Tow and 75 mm Castors

The run from door to handling position is 300 m, the shell weighs 20 kg, and four 75 mm castors carry it. At 1.1 m/s the tow takes 4.6 minutes, and 40 s goes on the 20 mm apron joints, where a 75 mm wheel against a 20 mm gap gives 3.75 and anything under 4 catches.

With a 180 mm centre of gravity on a 550 mm footprint, tipping needs 1.53 g sideways. Crossfall is 1% and a turn applies 0.15 g, leaving 1.38 g of margin, which is why this ground support case has no telescopic handle: it would raise the centre of gravity 200 mm and drop the threshold to 0.72 g.

At 55 °C the wheels lose 15% hardness and rolling resistance rises 12%, adding 30 s.

Conclusion

A ground support case is designed from a 25 minute turnaround rather than from capacity. Three seconds to open, 8 s per item and 4.6 minutes for the 300 m tow set the shell at 20 kg and 550×400×250 mm, with the lid held at 105°. Twelve compartments in four colours follow the turnaround order.