And a 406 ELT will broadcast your gps position instantly to SAR.
Nope. Only if it has been interfaced with onboard GPS equipment will it transmit coordinates. If it has a built-in GPS, that GPS has to boot up when the G-switch fires (or the panel switch is actuated) and it has to find satellites and figure out where it is, then transmit the coordinates.
And it's not instant. As someone else pointed out, there is usually a 50-second delay. Plenty of time for the airplane to sink or burn or explode or whatever.
The common 406 works on the same doppler principle as the old 121.5. The higher frequency, and better frequency stability, gives better and tighter resolution for location, but it still leaves a radius to search. It also transmits a 121.5 signal for the SAR guys to home in on once they're in the area.
And that 406 must be registered with the appropriate national registry for it to be of any real use. The 406 is encoded with the 24-digit transponder code assigned to the airplane's registration, so that if they get an ELT signal that identifies itself as being from N1234XY, the system checks the flight plans and will act quicker than if they think it might be a false alarm. And they know who to contact if they get a signal, since the owner must provide contact information for himself and several other people. Rogue ELTs can be shut off way sooner, saving everyone a lot of headache trying to figure out whose ELT is chirping away.
I often find 406s improperly mounted. It seems that the guys doing the installations aren't reading the whole installation manual, or are just ignoring it. Artex, for instance, has this to say about the mounting:
RTCA
1)DO-204, § 3.1.8 guidelines for mounting a ELT:
a)The ELT shall be mounted to primary aircraft load carrying structures, such as trusses, bulkheads,
longerons, spars, or floor beams.
b)The mounts shall have a maximum static local deflection no greater than 0.1 inches (2.5 mm) when
a force of 100 lbs (450 newtons) is applied to the mount in the most flexible direction. Deflection
measurements shall be made with reference to another part of the aircraft not less than 1 foot (0.3
meters) nor more than 3 feet (1.0 meters) from the mounting location.
2)DO-182, § 6.2.2.b recommends that:
a)To maximize the probability of the ELT transmitting a detectable signal after a crash, all ELT system
components, which must survive a crash intact, e.g. transmitter and external antenna, should be
attached to the airframe in such a manner that the attachment system can support a 100g load,
(ELT weight x 100, ELT antenna weight x 100, etc.) applied through the center of gravity of the
component (ELT, antenna, etc.) in the plus and minus directions of the three principal axes of the
aircraft.
b)Post-crash critical components of the ELT system, e.g. transmitter and external antenna, should be
mounted as close to each other as possible.
c)The antenna coax cable should not cross any production breaks, e.g., major structure sections, such
that the ELT and antenna are in the same section of the aircraft and as close together as possible.
d)If the ELT and external antenna are on opposite sides of an airframe production break, the
components should be secured to each other by a tether that can support a 100g
load (ELT weightx 100). The interconnecting antenna-to-ELT coax cable should have sufficient slack on both ends
that it will not be subjected to any tensile load and should be tied loosely to the tether.
Location
CAUTION: MANY ORIGINAL ELT INSTALLATIONS ARE INADEQUATE AS FAR AS UNIT LOCATION AND
SURFACE RIGIDITY ARE CONCERNED. BECAUSE OF THE CRITICAL FUNCTION AN ELT
PERFORMS, IT IS IMPORTANT THE INSTALLATION FOLLOWS THE INSTRUCTIONS AND
RECOMMENDATIONS HEREIN.
CAUTION: THE MOUNTING SURFACE MUST BE EXTREMELY RIGID; THEREFORE, MOUNTING AN ELT
DIRECTLY TO THE AIRCRAFT SKIN IS UNACCEPTABLE. MOUNTING THE ELT DIRECTLY TO
THE AIRCRAFT SKIN INDUCES “CRASH HIDING” VIBRATIONS AND PROVIDES A VERY
POOR MOUNTING SURFACE.
CAUTION: AVOID LOCATING THE ELT WHERE IT WILL BE SUBJECTED TO UNPROTECTED EXPOSURE
TO HARSH CHEMICAL FLUIDS SUCH AS DEICING COMPOUNDS. THESE TYPES OF CHEMICAL FLUIDS CAN PROMOTE
CRACKING AND FRACTURING OF THE ELT MOUNTING FRAME AND HOUSING COMPONENTS BYDEGRADING
THE STRUCTURAL INTEGRITY OF THESE COMPONENTS. THESE SAME CHEMICAL AGENTS MAY ALSO CAUSE CORROSION
OF ELECTRICAL CONNECTIONS.
WARNING: AVOID LOCATING THE ELT IN SUCH A LOCATION WHERE IT MAY BE SUBJECT TO FLYING
OBJECTS OR AIRCRAFT STRUCTURAL PARTS THAT MAY IMPACT THE ELT DURING ANAIRCRAFT CRASH.
MOUNTING AN ELT IN A VULNERABLE AREA CAN RESULT IN ANIMPACT BEYOND THE ELT'S TSO CRASH RATING OF 100G,
CAUSING DAMAGE AND PREVENTING CORRECT OPERATION DURING A POST-CRASH ENVIRONMENT.
I regularly find 406s installed way out of conformity with these requirements. The old ELTs were often mounted to a bracket riveted to the aircraft skin, and they're way too flexible. You can't just bolt the new ELT to that old mount. False alarms, or failure to trigger in a crash, become much more likely. I find them sitting right in baggage compartments where they get bashed, the cables get torn, the switch gets bumped to "On." The owner has paid for an ELT that might not save him, simply because the installer didn't do the job properly.
