Re Build of N94978 BC12-d

[astjp2]

Re: Re Build of N94978 BC12-d

Dave, see above, its the RTC DO requirement for the elt, 43.13-b just tells you how to meet the requirement for the load test on any avionic shelf, an adel clamp wont meet the spec for an elt. Tim

I will try to download the spec when I get to work and upload it to the tech reference section. It seems like a lot of people on here push back if I don't provide all of the supporting documents and addendums...it only took me 2 hours to find what the installation requirements are, now to get them posted

Maybe I should charge by the hour for research????? even though it makes me a better IA

Re: Re Build of N94978 BC12-d

So what uses plywood (shown in figure 2-10) besides a floor? I think its passing through the plywood floor and attaching to the structural tubing....but it still does not qualify the elt mounting requirements.

Tim,

I don't read it that way, here's why; the plywood is labeled "plywood", then the plywood does not lay over top of the tube and floors do, also the title says "TYPICAL ATTACHMENT OF SUPPORT STRUCTURE... the only thing that is attached to the tube is the plywood so I think the plywood is the the support structure being referred to.

Having said all that and holding that opinion about the figure I have to say that after re-reading the text I am wondering if that is merely a support for avionics in general and not necessarily for an ELT. Although I suppose that could be debated.

Dave

[astjp2]

Re: Re Build of N94978 BC12-d

Following are the FAA guidelines for mounting a TSO-C91a ELT, per RTCA
DO-183 paragraph 3.1.8:
1. “The ELT shall be mounted to primary aircraft load carrying structures such as
trusses bullheads, longerons, spars, or floor beams.”

2. “The mounts shall have a maximum static local deflection no greater than 2.5
mm (0.1 in) when a force of 451 Newtons (100lbs) is applied to the mount in the most
flexible direction. Deflection measurements shall be made with reference to another
part of the airframe not less than 0.3 meters (3 feet) from the mounting location.”
In addition, RTCA Document number DO-182 recommends that “all ELT system
components which must survive a crash intact, should be attached to the airframe in
such a manner that the attachment system can support a 100g load…in the plus and
minus directions of the three principal axes of the aircraft.”

The ELT must be mounted with the arrow which is printed on the battery case
pointing in the direction of flight. The ELT should be mounted with its longitudinal
axis aligned within 10 degrees of the longitudinal axis of the aircraft fuselage. Avoid
mounting the ELT near sources of strong EMI/RFI radiation. (See Fig. 1)

If this is a new installation or if the current installation is unacceptable, find a location
per the following:
RTCA suggests the aft section of the fuselage. Statistically, this is the least likely
section of the aircraft to receive damage in a crash. It is also near the antenna
connection, minimizing cable length between the transmitter and antenna. Maintain
access for maintenance. If possible, avoid locating the ELT where it will be subjected
to chemical fluids such as deicing compounds, cleaning fluids, etc. Over time, these
may attack the plastic and metal components.

The mounting location must conform to the requirements of RTCA DO-204A and AC
43.13-2A. DO-204A Sec 3.1.8 states:
"The ELT shall be mounted to primary aircraft load carrying structures such as
trusses, bulkheads, longerons, spars, or floor beams (not aircraft skin). The mounts
shall have a maximum static local deflection no greater than 2.5 mm (0.1 in.) when a
force of 450 Newton's (100 Ibs) is applied to the mount in the most flexible direction.
Deflection measurements shall be made with reference to another part of the airframe
not less than 0.3 meters (1 foot) nor more than 1.0 m (three feet) from the mounting
location."

[astjp2]

Re: Re Build of N94978 BC12-d

So what uses plywood (shown in figure 2-10) besides a floor? I think its passing through the plywood floor and attaching to the structural tubing....but it still does not qualify the elt mounting requirements.

No not so, its for other than floorboards, here is the text description from AC43.13-2b "FIGURE 2-10. TYPICAL ATTACHMENT OF SUPPORT STRUCTURE TO TUBULAR FRAME OTHER THAN STRUCTURE TO FLOOR"

[astjp2]

Re: Re Build of N94978 BC12-d

Every ELT requires the same load check requirements....some just tell you what they are.

Re: Re Build of N94978 BC12-d

This quote is from an ACK ELT manual. If you're installing some other mfg of ELT it doesn't apply. AC43.13 2B Chapter 1 Structural Data and Chapter 2 Com, Nav, and ELT installations lay it out very nicely.
And to muddy the waters even more, in a legal interpretation by the FAA Office of the Chief Counsel: The Aircraft Maintenance Division (AFS-300) in the Office of Flight Standards Office has expressed the view that the installation of a TSO ELT in a small airplane using methods, techniques, and practices contained in AC 43.13-2B would not constitute a major alteration to the aircraft. In view of the definition of a major alteration, we concur with that determination. Accordingly completion of an FAA Form 337 would not be required." You can retrieve the legal interpretation from the FAA website.

Garry

What's a major alt? Yeah that's a debate isn't it.

There have been some FSDO folks and others saying that items listed in the TCDS can be major alt's and require a 337. I asked for an interpretation and the chief counsel says anything in the TCDS item list is not ever a major alt. No surprise I think.

So twice now I like the chief counsel's statement. Usually we complain that the FAA makes no sense. Two cases here where they do.

Dave

Re: Re Build of N94978 BC12-d

that clamp is for mounting something like a plywood floor board in a cub, still does not meet the .100 at 100 lb requirement for an elt

No not so, its for other than floorboards, here is the text description from AC43.13-2b "FIGURE 2-10. TYPICAL ATTACHMENT OF SUPPORT STRUCTURE TO TUBULAR FRAME OTHER THAN STRUCTURE TO FLOOR"

[Garry Crookham]

Re: Re Build of N94978 BC12-d

I found another requirement, adel clamps would exceed the .100 movement,

The mounts shall have a maximum static local deflection no greater than 2.5mm (0.1 inch) when a force of 450 newton's (100lbs.) is applied to the mount in the most flexible direction. Deflection measurements shall be made with reference to another part of the airframe not less than 0.3 meter (1 foot) nor more than 1.0 meter (3 feet) from the mounting location

http://www.supercub.org/forum/showth...-in-Supercubs&

This quote is from an ACK ELT manual. If you're installing some other mfg of ELT it doesn't apply. AC43.13 2B Chapter 1 Structural Data and Chapter 2 Com, Nav, and ELT installations lay it out very nicely.
And to muddy the waters even more, in a legal interpretation by the FAA Office of the Chief Counsel: The Aircraft Maintenance Division (AFS-300) in the Office of Flight Standards Office has expressed the view that the installation of a TSO ELT in a small airplane using methods, techniques, and practices contained in AC 43.13-2B would not constitute a major alteration to the aircraft. In view of the definition of a major alteration, we concur with that determination. Accordingly completion of an FAA Form 337 would not be required." You can retrieve the legal interpretation from the FAA website.

Garry

[PA1195]

Re: Re Build of N94978 BC12-d

The link Tim provided is worth a read...some unpleasantness awaits those whose ELT goes off w/o reasonable cause and the Administrator gets involved in its installation.

I have an ACK 406 that was previously installed, and sits aft of the extended baggage's metal bulkhead mounted to a horizontal metal plate. Don't recall the hardware used...it's too tight for me to crawl back in that hole. Its remote control and audio alarm are on/behind the instrument panel. Non-shielded (?) wiring (looks like phone telcom cabling) connects the aft and forward components. RF ingress may eventually be a problem as noted in the link.

Any way after 40+ years of self contained EBC 102A 121.5 mHz units that I "might" be able to activate and/or remove from the wreck, now there's an ELT hidden where I can't get to, can't retrieve without cutting the fabric, and is subject to loss of the coax connections and antenna in an upset. That's what happened in the Senator Ted Stevens wreck I linked above...no signal after impact.

A Delorme Inreach or SPOT unit sitting on the console top might be a better option if alerting help and portability is the goal.

Gary

[astjp2]

Re: Re Build of N94978 BC12-d

that clamp is for mounting something like a plywood floor board in a cub, still does not meet the .100 at 100 lb requirement for an elt

Re: Re Build of N94978 BC12-d

Doesn't AC43.13-2b show a clamp being used for mounting in figure 2-10?

It's an AN742 clamp not an Adel but I suspect that is of little consequence, we can get Adels with or without rubber and in various metals (steel, SS, aluminum) as I recall.

What am I missing?

Dave

[astjp2]

Re: Re Build of N94978 BC12-d

I found another requirement, adel clamps would exceed the .100 movement,

The ELT shall be mounted to primary load-carrying structures such as trusses, bulkheads, longerons, spars, or floor beams. (not aircraft skin) The mounts shall have a maximum static local deflection no greater than 2.5mm (0.1 inch) when a force of 450 newton's (100lbs.) is applied to the mount in the most flexible direction. Deflection measurements shall be made with reference to another part of the airframe not less than 0.3 meter (1 foot) nor more than 1.0 meter (3 feet) from the mounting location

http://www.supercub.org/forum/showthread.php?44660-Practical-mounting-of-406-ELT-in-Supercubs&

[astjp2]

Re: Re Build of N94978 BC12-d

It was an interpretation of 91-44a para 6a, that the shock requirements necessary require hard mounting per ac43-13.2b which precludes using adel clamps since they are used to isolate vibrations (which is part of the shock requirement), they also interpreted something that says it cant be mounted to the outside skin incase the skin buckles, not allowing the appropriate shock condition (think Cessna skins). This was addressed in an IA seminar in Anchorage in 2009. It was news to me too. Now I just make billet aluminum blocks that bolt to the tubes with a plate. Not real expensive compared to what could be out there. Tim

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-44A.pdf

[Leenicklas]

Re: Re Build of N94978 BC12-d

Never had an ELT

[PA1195]

Re: Re Build of N94978 BC12-d

A NTSB report of an ELT, fastened via velcro, that departed its mount during a crash. Tore off the antenna coax. See pages 38-40 with pictures.

http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR1103.pdf

I'd be interested to see the no-Adel Circular.

Gary