14 CFR Part 25.787: Stowage Compartments
In this post, we will dig into the next regulation, 14 CFR Part 25.787. This one is related to cabin stowage compartments. It is more relevant to the interior cabin or cargo areas of the aircraft.
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(a) Each compartment for the stowage of cargo, baggage, carry-on articles, and equipment (such as life rafts), and any other stowage compartment, must be designed for its placarded maximum weight of contents and for the critical load distribution at the appropriate maximum load factors corresponding to the specified flight and ground load conditions, and to those emergency landing conditions of § 25.561(b)(3) for which the breaking loose of the contents of such compartments in the specified direction could -
(1) Cause direct injury to occupants;
(2) Penetrate fuel tanks or lines or cause fire or explosion hazard by damage to adjacent systems; or
(3) Nullify any of the escape facilities provided for use after an emergency landing.
(b) There must be a means to prevent the contents in the compartments from becoming a hazard by shifting, under the loads specified in paragraph (a) of this section. For stowage compartments in the passenger and crew cabin, if the means used is a latched door, the design must take into consideration the wear and deterioration expected in service.
(c) If cargo compartment lamps are installed, each lamp must be installed so as to prevent contact between lamp bulb and cargo.
In the previous posts, we looked at:
- 14 CFR Subpart C Section 25-301: Loads
- 14 CFR Subpart C Section 25-303: Factor of Safety
- 14 CFR Subpart C Section 25-305: Strength and Deformation
- 14 CFR Subpart C Section 25-307: Proof of Structure
- 14 CFR Subpart C Section 25-365: Pressurized Compartment Loads
- 14 CFR Subpart C Section 25-561: General Emergency Landing Ultimate Loads
- 14 CFR Subpart C Section 25-562: Emergency Landing Dynamic Loads
- 14 CFR Subpart C Section 25-601: Hazardous Unreliable Design Features
- 14 CFR Subpart C Section 25-603: Materials
- 14 CFR Subpart C Section 25-605: Fabrication Methods
- 14 CFR Subpart C Section 25-607: Fasteners
- 14 CFR Subpart C Section 25-609: Structure Protection
- 14 CFR Subpart C Section 25-613: Strength of Materials
- 14 CFR Subpart C Section 25.619-625: Fitting Factor
(a) Stowage Compartments: Load Factors
Throughout the cabin of a large aircraft, there can be literally hundreds of different stowage compartments. Some examples are as follows:
- Emergency Equipment Stowage Compartments
- Miscellaneous Stowage Compartments
- Coat Rod Stowage Compartments
- Standard Unit Stowage Compartments
- Half and Full Size Meal Cart Stowage Compartments
- Overhead Baggage Stowage Compartments
- Oven or Microwave Stowage Compartments
- PSU Stowage Compartments
Stowage Compartments: Placards
Any of these stowage compartments may face any direction, FWD/Aft or Side or DOWN directions. In each case, the contents must be secured.
A placard is a small sheet metal label that indicates the maximum certified weight that the compartment can hold, and other details. There maybe thousands of these little placards in a large aircraft, indicating various things to the cabin crew and passengers.
Stowage Compartments: Loading
Stowage compartments restraint devices (doors, latches, quarter turns etc.) must be certified to the maximum load factors and under the worst possible loading conditions.
For example, consider a large compartment door (loose contents) facing the FWD direction with a latch at the top and bottom. The worst possible loading would be a bottom concentrated load with the bottom latch disengaged. Similarly, to account for load shifting a 60-40 load ratio may be used. This is done to analyze the restraint devices on each side of the door including the door latch assembly, the door hinge assembly and associated hardware.
Stowage Compartments: Enclosure
The regulation also mandates full enclosure of stowage compartments for more than 10 seats. This means that the stowage compartments must include doors with latches, or appropriate restraint devices to enclose the contents completely.
Stowage Compartments: Volumetric Density
The regulation does not provide any specifics on the density to be used for the contents of stowage compartments that are meant for miscellaneous stowage. This guidance may be provided by the DER.
In general the highest density is 10 lb/ft^3, this may decrease based on the height of the CG points of the stowage compartments. However, for overhead stowage the DER may specify 10 lb/ft^3. In addition, there may be DER requirements for higher densities or rounding off of the placard maximum weights to the nearest 5 lb.
Stowage Compartments: Spring Loaded Doors
Another variation of compliance to this regulation is the possibility that a non spring loaded door is in the way of a rapid emergency evacuation. Such doors are designed to always close using a spring loaded door hinge mechanism to meet compliance requirements of this regulation.
Stowage Compartments: Safety
The key to compliance is 'safety'. The contents should not break free due to non-inclusive loading and result in any of the (1) (2) or (3) conditions as noted in part (a) of the regulation.
(b) Stowage Compartments: Shifting and 'Wear and Tear'
It is possible that the contents within the stowage compartments may shift during flight. In some cases, this can damage the fiberglass skin of the stowage compartments panels.
For example, standard units or meal carts are usually made from metal casings with sharp corners. Rubstrips and other features not only serve as protection against panel puncture from these contents, but also as a means to constrain the contents from shifting and imposing unexpected loading on the restraint devices.
In the case of the cargo areas, the shifting of the baggage can cause huge issues. The overall CG of the baggage compartment can shift so much that it can be a hazard to safe flight controls. This is the reason for using cargo nets, strap down nets and other restraint devices in the cargo bay.
There are two ways to ensure compliance to the 'wear and tear' component of part (b) of this regulation.
Stowage Compartments: Door Dual Latching
One acceptable way to comply with part (b) is by providing dual latching mechanisms on the doors of stowage compartments.
On larger doors there may be two latches spaced farther apart, with a single bolt in each latch. Both may have to be engaged manually. Optionally, one of the latch bolts may be spring loaded, and the other has to be engaged manually.
On smaller doors, there may be one single latch with two bolts, either both manual or one spring loaded and one manual.
Stowage Compartments: 1.33 wear and tear factor
Latches and quarter turns are restraint devices that are frequently engaged and disengaged. Dual latch design practice ensures compliance with the wear and tear requirement. However, each bolt must be shown good for the total load, including the 1.33 wear and tear factor.
The idea is that for certification by analysis purposes, one bolt is assumed to be disengaged or failed under the ultimate load per 14 CFR Subpart C Section 25-561.
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