ELT Fact???

[isuhawkeye]

Several years ago I went through the AFRCC SMC course, and the instructors made a point of explaining what they dubbed The rule of Seven

Under this rule

ELT's become activated at 7 G's
They get broken at 70 G's
The average load at impact is 700 G's

This did a lot to explain why so many catastrophic accidents have no ELT signal. 

Has anyone heard of this, or can anyone validate these numbers

[RiverAux]

They didn't mention those numbers when I took it.  Wonder what the difference in those stats would be for the old ELTs and the new 406s?

[Eclipse]

Sounds like a wives tail to me.  EBC's website is light on info, but does indicate its units will take 1000 G's.

And considering the minutia of testing and the importance of the device to life safety, I would think
something like a "7-7-7 rule of thumb" which effectively means "ELT's = useless" would have been addressed decades ago - SARSAT was started in 1969, after a young woman died of starvation when she was stranded for over 50 days after surviving a plane crash.

http://www.emergencybeaconcorp.com/transmitters/ebc_502.htm

http://www.wsdot.wa.gov/aviation/SAR/ELT_History.htm

[♠SARKID♠]

Sounds like a wives tail to me.  EBC's website is light on info, but does indicate its units will take 1000 G's.

And considering the minutia of testing and the importance of the device to life safety, I would think
something like a "7-7-7 rule of thumb" which effectively means "ELT's = useless" would have been addressed decades ago - SARSAT was started in 1969, after a young woman died of starvation when she was stranded for over 50 days after surviving a plane crash.

http://www.emergencybeaconcorp.com/transmitters/ebc_502.htm

http://www.wsdot.wa.gov/aviation/SAR/ELT_History.htm

You're close.  It was the woman that sparked it, but it probably wouldnt have gotten far if the senators hadnt gone missing.

[Fifinella]

Per the POH, the ELT on a Cessna 172N is activated at 5G's.

[sardak]

Correction to ELT history.
The 1967 crash resulted in mandatory ELT laws, eventually.

Cospas-Sarsat was created in 1979 and the first Sarsat package was launched in 1982.  The 25th anniversary celebration is next month in Washington, DC.

As for the crash numbers, I've never heard of them before and they seem just a bit too convenient.

Mike

[isuhawkeye]

This is not intended to be a thread referencing ELT history.  I haveposted information regarding the survivability of ELT's.

Thanks

[Major Lord]

Acceleration and Deceleration.

To pull:

7 Gs = 225.2183 Ft Per sec sq

70 Gs = 2252.183 Ft per sec sq

700 G's22, 521.83 Ft per sec sq.


The 70 and 700 G numbers sound a little on the high side to me for a rule of thumb, but I am not a physicist.

Major Lord

[sardak]

Performance requirements for ELTs are contained in three documents:
RTCA (formerly Radio Technical Commission for Aeronautics)
DO-183 for 121.5/243 ELTS
DO-204 for 406 ELTs
DO-183 is currently being merged into DO-204.
European Organization for Civil Aviation Equipment (EUROCAE)
ED62 for all ELTs, which is being revised concurrent with DO-204.
The European specs are tighter than US specs.

These specs are for current generation ELTs.  Old ELTs, which are still legal in the US, don't have to meet these.

Those documents require many tests for ELTs.  After each basic operational test, an automatic ELT (one with a g-switch or crash sensor) must activate at
3 g's with a change in velocity of 4.5 ft/sec

The crash test shocks are:
500 g's for 4 milliseconds in each of 6 directions (up, down, forward, backwards, right, left)
the ELT may or may not activate
THEN
100 g's in the  6 directions for 23 milliseconds
the ELT must activate (or stay activated) and remain in its mount.

Compare these numbers to those cited by AFRCC.

The crash sensor itself must also meet certain specs.
Activation and non-activation pulses must be applied at least at 3, 6, 9 and 12 g's.
The sensor must still work after a 30g cross load.

The sensor cannot activate at less than 2.3G and a change in velocity of less than 4.5 ft/sec.  Note that 2.3G doesn't necessarily equal 2.3g, but is way too technical to explain here and no one cares anyway.

Other tests.

Penetration test.  A 55 lb aluminum mass with a flat impact surface of 1 inch x 0.25 inch dropped from at least 6 inches onto all six sides of the ELT.  The ELT must still work.

Crush test. Each side of the ELT must support a load covering the entire surface at 100 psi for 5 minutes.

Flame test. ELT is placed 1 meter over burning 100LL avgas for 15 sec and must still work.

Optional fire test. ELT is placed in a fire that completely envelopes the ELT for at least 2 minutes and still must work.

And for the deployable ELTs discussed in another thread, they must still work after an impact at 55 mph on a hard surface (concrete, rock, steel, etc.).

Mike

[isuhawkeye]

Hey Mike,

Thanks so much for the numbers. 

I wish I payed more atention to my friends senoior thesis measuring aircraft crash impact forces.....

can anyone site G measurments in actual crash environments.