Emergency Landing Dynamic Loads

We will try to understand what it means for interior structures other than seats, in terms of emergency landing dynamic loads. In this post we will dig into the next regulation, 14 CFR Subpart C Section 2-562.

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§ 25.562 - Emergency Landing Dynamic Loads

(a) The seat and restraint system in the airplane must be designed as prescribed in this section to protect each occupant during an emergency landing condition when—
(1) Proper use is made of seats, safety belts, and shoulder harnesses provided for in the design; and
(2) The occupant is exposed to loads resulting from the conditions prescribed in this section.
(b) Each seat type design approved for crew or passenger occupancy during takeoff and landing must successfully complete dynamic tests or be demonstrated by rational analysis based on dynamic tests of a similar type seat, in accordance with each of the following emergency landing conditions. The tests must be conducted with an occupant simulated by a 170-pound anthropomorphic test dummy, as defined by 49 CFR Part 572, Subpart B, or its equivalent, sitting in the normal upright position.
(1) A change in downward vertical velocity (Δ v) of not less than 35 feet per second, with the airplane's longitudinal axis canted downward 30 degrees with respect to the horizontal plane and with the wings level. Peak floor deceleration must occur in not more than 0.08 seconds after impact and must reach a minimum of 14g.
(2) A change in forward longitudinal velocity (Δ v) of not less than 44 feet per second, with the airplane's longitudinal axis horizontal and yawed 10 degrees either right or left, whichever would cause the greatest likelihood of the upper torso restraint system (where installed) moving off the occupant's shoulder, and with the wings level. Peak floor deceleration must occur in not more than 0.09 seconds after impact and must reach a minimum of 16g. Where floor rails or floor fittings are used to attach the seating devices to the test fixture, the rails or fittings must be misaligned with respect to the adjacent set of rails or fittings by at least 10 degrees vertically (i.e., out of Parallel) with one rolled 10 degrees.
(c) The following performance measures must not be exceeded during the dynamic tests conducted in accordance with paragraph (b) of this section:
(1) Where upper torso straps are used for crew members, tension loads in individual straps must not exceed 1,750 pounds. If dual straps are used for restraining the upper torso, the total strap tension loads must not exceed 2,000 pounds.
(2) The maximum compressive load measured between the pelvis and the lumbar column of the anthropomorphic dummy must not exceed 1,500 pounds.
(3) The upper torso restraint straps (where installed) must remain on the occupant's shoulder during the impact.
(4) The lap safety belt must remain on the occupant's pelvis during the impact.
(5) Each occupant must be protected from serious head injury under the conditions prescribed in paragraph (b) of this section. Where head contact with seats or other structure can occur, protection must be provided so that the head impact does not exceed a Head Injury Criterion (HIC) of 1,000 units. The level of HIC is defined by the equation:

 

Dynamic Loads HIC Formula

 

Where:
t1 is the initial integration time,
t2 is the final integration time, and
a(t) is the total acceleration vs. time curve for the head strike, and where
(t) is in seconds, and (a) is in units of gravity (g).
(6) Where leg injuries may result from contact with seats or other structure, protection must be provided to prevent axially compressive loads exceeding 2,250 pounds in each femur.
(7) The seat must remain attached at all points of attachment, although the structure may have yielded.
(8) Seats must not yield under the tests specified in paragraphs (b)(1) and (b)(2) of this section to the extent they would impede rapid evacuation of the airplane occupants.
[Amdt. 25-64, 53 FR 17646, May 17, 1988]


In the previous posts, we looked at:

14 CFR Subpart C Section 25-562 provides guidelines on emergency landing dynamic loads specifically related to seats, all kinds of seats such as passenger seats, FA seats, and even jump seats (these are flip up cushion seats attached to interior monuments used by flight crew).

Emergency Landing Dynamic Loads - Interiors Structures Related Stuff

OK, this regulation pretty much deals exclusively with seats, their attachments to the seat track floor structure, their dynamic test conditions for certification etc.

So what does this have anything to do with the other monument structures such as bulkheads or partitions/dividers or galleys or lavatories?

It does have an indirect impact. Let us examine these impacts below.

 

 

Monument Stiffness and Head Injury Criteria (HIC):

The regulation specifies the load factors and testing requirements for seat certification. And these tests are dynamic tests. The seats are accelerated to 16G and then brought to a total stop as specified in the regulation within a specific time period.

If you cannot see the video above, click this link: Emergency Landing Dynamic Loads Seat Test Video

Generally, anytime there is a monument in front of a row of seats, the common practice is to maintain a gap that is large enough that the test dummy head misses it completely.

But when this is not possible for whatever reason, then the stiffness of the monument in front of the seats becomes important. This is because the test must simulate the contact between the test dummy head and the monument structure in front of it, to meet the stringent HIC criteria for certification.

As we can see in the video above, passenger seats only have the waist harness. The dummy head is moving and basically hits the knees. But if it is obstructed by a windscreen or a partition for example, then the HIC number due to the emergency landing dynamic load test requirement may be too high to certify the seat and the layout of passengers (LOPA).

This dynamic load may also need to be considered as a separate load case if other load cases are not as critical to certify that monument.

Flight Loads for Jump Seats:

From the Ultimate Loads post, we know that there are certain load cases that are specific to in flight turbulence, for example the 6.5G DOWN flight load case.

Emergency Landing Dynamic Loads Jump Seat
Emergency Landing Dynamic Loads Jump Seat (Credit Getty Images)

Jump seats are not supposed to be used as TTL seats, meaning they are not allowed to be used for Taxi Takeoff Landing (TTL). And they do not have any seat track attachments like normal TTL seats do.

Therefore, emergency landing dynamic loads are not applicable. However, the DOWN flight loads are significant, especially considering the weight of the crew member and the seat weight itself.

Typical weight that is used for jump seat certification is 220lb which includes the FAA dummy weight of about 170lb and roughly 50lb for the seat installation. But some DERs may allow a lower weight based on their own experience.

So why are we talking about flight loads all of a sudden?

Because there is a tangent effect that needs to be considered for jump seats attached to monuments.

Just like the seat belts, the jump seats and attachments are also required to be certified for severe wear and tear factor of 1.33, due to frequent in flight use.

Although not common, some DERs may require that this factor be extended to the monument structure attachments (such as floor fitting installations) to the aircraft structure under this jump seat. So keep this in mind and do not be alarmed if it happens to you, you heard it from me, 🙂

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Surya Batchu
Surya Batchu

Surya Batchu is the founder of Stress Ebook LLC. A senior stress engineer specializing in aerospace stress analysis and finite element analysis, Surya has close to a decade and a half of real world industry experience. He shares his expertise with you on this blog and the website via paid courses, so you can benefit from it and get ahead in your own career.