Crash Safety g Loads

[TheLucifer]

Hi all,

I have a major problem on defining g loads for ceash safety qualification tests. RTCA DO 160E Chapter 7 Defines 20g for 11-20 ms, while MIL-STD-810F Method 516.5 chapter 4.5.6.1 defines 40g's for 15-23 ms's.

IMHO, 40g is not a logical test level for aircraft other than fighters, -which may crash with very high speeds- but I need a proof, an opinion is not enough to convince qualification guys. Does anyone have any experience on these standards?

 

[der8110]

Those that have the experience wrote the standards. There is nothing unusual about a 20g or 40g crash, humans can survive 50g if properly restrained. It is not the speed that matters, it's the deceleration ("speed never hurt nobody"). Besides, takeoff and landing speeds (where most crashes occur) are relatively similar for fighters and transports. Flight into a mountaintop at cruise speed is extremely rare, in supersonic dash even more rare.

Your hope lies in what the equipment is used for; who cares if a passenger entertainment system works after a crash, but it is critical for cockpit voice recorders to survive.

 

[rb1957]

i think the OP was drawing attention to incompatable requirements. i guess, without knowing the reports well, that you pick one (if you can) or use the one you're told to, and run.

i think der8110 has a good point about the function of the box, but i think the problems mostly arise from holding the box down (then the FARs make a distinction between in-cabin equipment (that can hurt pax) and out-of-cabin equipment.

 

[scotty7]

15 years ago a Boeing 737 crashed in England (Kegworth). 47 dead, 79 survived.
From the incident report

http://www.aaib.gov.uk/sites/aaib/cms_resources/dft_avsafety_pdf_502831.pdf

we get this:
Seats designed for 16g collapsed and some broke away in an accident with a probable peak g loading of 22 -28g (p106). Within the physiological limits of the passenger. Seats collapsed, and all but 14 of the passengers sustained injury to their legs to the extent that they could not contribute significantly to their egress (p48).
The impact speed was 90 knots.
So yes, 40g is a pretty good number to go for.

 

[rb1957]

yes we have 16g seats, but we still use 9g for items of mass in the cabin

 

[IRstuff]

Back to the OP, say what?

need a proof, an opinion is not enough to convince qualification guys

Since when to do the test guys get to decide what the specification is? They are not allowed to be "convinced." The specification is what they are supposed to do. Just what is your specification?

Surely, you didn't get all the way to qual BEFORE figuring what the design requirements are? What does your contract or specification say?

TTFN

 

[rb1957]

i interpreted "qualification" as "certification"

 

[IRstuff]

If so, then OP is screwed because his company failed to read the directions or he's trying to buck the requirement.

His question then doesn't make any sense, because the requirement is the requirement

TTFN

 

[TheLucifer]

OK, it seems like I have to go into some details.

My company is about to design a new aircraft, which will be certified according to EASA CS 23. CS 23 directives about crash safety are 18g's in each directions. But also, there is a second qualification authority. Requirements of this authority is forming nowadays, including environmental qualification requirements.
Environmental qualification of this aircraft will be customized with requirements from RTCA DO 160E & MIL STD 810F. We are now in contract & specification negotiation phase. That's why I can't simply open the specification and do what it says: I'm a member of specification writing group.

Of course, standards are written by the grizzliest guys of aviation industry, I'm not questioning their experiences. But there are two standards which say different things. If I chose RTCA-DO, I have to find a good proof for qualification group. If I chose MIL, which has higher requirements, I have to have a proof for my boss. That's why I'm looking for someone, which experienced a similar situation.