Moderators: sky's the limit, sepia, Sulako, North Shore
Not usually in a small aircraft but EMI is dealt with before and after so it's really no issue.
Correct. Changing the location of a conductor can result in unintended EMI affects.
(9) affect a communication system required by the approved type design?
I have found twice during certification testing that the installation of a conductor not associated with avionics or aircraft systems, none the less, introduced an EMI affect, which resulted in the GPS being unable to receive the satellite signals, and going off line. There is a specific certification EMI test (specified by TC) which I conduct on such wiring installations, to assure that compliance remains shown.(10) affect instruments, or indicators that are installed as part of a system required by the approved type design?
explain...There is a specific certification EMI test (specified by TC) which I conduct on such wiring installations, to assure that compliance remains shown.
I'll presume a "please..." associated with that somewhere - this is what I do for a living....explain...
This test has failed on two aircraft I have tested, and wiring location changes were required to obtain a pass. Neither of the aircraft had a comm nor GPS change conducted, it was non aircraft system wiring which had been changed, and caused the undesired affect.5.2 Test Frequencies
When testing VHF Comms as a Source, the ten test frequencies shown below will be selected when assessing the GPS as the Victim.
121.150, 121.175, 121.185, 121.190, 121.200, 131.250, 130.285, 131,250, 131.275, 131.290 131.300 MHz.
The lack of interference from VHF radios will be demonstrated on the completed installation by tuning each VHF transmitter to the frequencies listed below and transmitting for a period of 35 seconds, or the longest uninterrupted transmission possible for that transmitter, while observing the signal status of each satellite being received. Degradation of individually received satellite signals below a point where navigation is no longer possible is not acceptable
In this regard, what you "know" is incorrect. TC occasionally witnesses EMC/EMI tests of whole aircraft, and may choose to involve themselves as a witness to any certification test. It was a TC witnessed EMI test which revealed the Comm frequency vs GPS issue, as the witnessing TC Engineer told me himself about the event. More commonly, DAR's witness these whole aircraft EMC/EMI tests for major mod approval, as delegated by TC, prior to issuing an STC for the mod. Such a test is a requirement under 2X.1301, and will be specified for nearly any electrical mod to be approved by STC.EMC test of the aircraft...which I know TC does not do
No, I know what I'm talking about. The EMC/EMI test will be specific to the whole aircraft as modified ('cause that what 571 Appendix A applies to), not any particular piece of installed equipment. The client might elect to resolve EMI non compliance with specific "fixes", which is fine if such a solution is acceptable for that unit. As such, it could be included in the final approved installation, with data acceptable to the signatory.Your talking about a specific unit...the GPS...which is why there are special filters you install at the RF fitting at the back of the GPS radio tray during an installation.
I don't know what you mean by "does not do". If it means they don't care about any potential EMC from a mod, you are absolutely wrong. This is the point in my post when I realize that if I try to pick apart everything you stated, I'd be here all day....just as I thought...nothing to do with an EMC test of the aircraft...which I know TC does not do
Why would anyone think that TC (= the taxpayer = you and I) pay a bill for witnessing a test for a private mod approval applicant? They don't pay the bill, they bill! Cost recovery!TC isn't paying the bill CID.
TC does not make you do anything. TC will accept a test plan you might propose to demonstrate compliance for a mod approval you have requested. If you want TC to not make you do anything, get away from airplanes.TC makes you do them...makes you pay...big money
You mean that there was no problem, the test was a pass, they witnessed that, found design compliance, and went home with that step completed, and your being closer to having the approval you applied for?! 'Sounds like a success to me!..then when there is no problem they go home and say oh well...
I'm sure it is, and based upon the nature of the aircraft and the mod, it could be very worthwhile. If a client wants to (or is required by TC to) send their aircraft to California for a very comprehensive EMI test, then they should do that. I don't witness tests like that, I just witness in accordance with a TC accepted test plan I prepare for the subject aircraft - I try to keep things reasonable for my clients!Sending the aircraft away to somewhere like California to have it EMC tested for a MAJOR MOD is absolutely done
Absolute proof that you don't have a clue. The standards are clear. Even if you are using AC 43.13. (Check 11-107) With respect to VHF COM and GPS, you are truly ignorant. VHF COM interference on GPS is well understood and MUST be explored when certifying them in aircraft.But if you think what you're doing with a comm and a gps is an EMC test?? Well............ with only VHF frequencies?
14-10. Interference - Electromagnetic Compatibility (EMC).
a. The equipment must not be the source of objectionable conducted or radiated interference, or be adversely affected by conducted or radiated interference from other equipment or systems installed in the aircraft.
b. Proper sensor equipment grounding is essential to ensuring EMC.
c. When possible, do not install positioning/navigation sensor(s) near a VHF radio.
d. The following paragraphs identify potential sources of interference and means of mitigating that interference:
(1) VHF communications harmonic, spurious, and local oscillator harmonics can cause interference. VHF interference can be mitigated by:
(a) Installing filters at the output of the VHF transmitter to prevent antenna-to-antenna interference. Such filters should have an insertion loss of 2 dB or less, or the installed VHF transceiver performance will have to be re-evaluated.
(b) Installing the positioning/navigation equipment as far away as feasible from any VHF transmitter equipment (to prevent case-to-case interference).
(c) Replacing the VHF equipment.
(2) An emergency locator transmitter (ELT) can re-radiate DME or VHF signals that can interfere with GNSS. Notch filters on the ELT antenna cable or replacing the ELT can eliminate this problem.
(3) DME has been known to cause interference to GNSS. Replacing the DME transceiver can eliminate the problem for some equipment. 111 3/28/14 AC 20-138D
(4) Direction finding equipment may cause interference. Moving the direction finding antenna to the belly of the aircraft has been found to eliminate this problem.
And....if you're interested incoming out of this fog of ignorance you're in, read this:23-1. Ground Test - GPS, GPS/SBAS, and GPS/GBAS.
21-1.1. Interference.
a. The lack of interference from VHF radios should be demonstrated on the completed
GNSS installation by tuning each VHF transmitter to the frequencies listed below and
transmitting for a period of 30 seconds while observing the signal status of each satellite being
received. Degradation of individually received satellite signals below a point where navigation
is no longer possible is not acceptable and will require that additional isolation measures be
taken. Re-evaluation of installed VHF transceiver performance is not necessary if the filter
insertion loss is 2 dB or less.
b. Evaluate the following VHF frequencies (25 kHz channels):
121.150 MHz 121.175 MHz
121.200 MHz 131.250 MHz
131.275 MHz 131.300 MHz
c. For VHF radios with 8.33 kHz channel spacing, evaluate the following additional
VHF frequencies:
121.185 MHz 121.190 MHz
130.285 MHz 131.290 MHz
d. For installations on rotorcraft, ensure that the rotor blades do not interfere with the
received signals. This problem has been experienced in some rotorcraft and varies with the
rotation rate.
....been putting GPS in A/C since 1989...all through their development...S/A...IFR approval...all that... I know what the issues are with EMI and GPS...so whatVHF COM interference on GPS is well understood and MUST be explored when certifying them in aircraft.
This reminds me of the occasional "reasoning" I've heard at the scene of a car strikes utility pole/tree/parked car etc. collision. The presence of the fixed item was the cause, the driver was not at fault, he was just driving along when he hit it, 'cause it was in the way!it fails the test only after I've moved the feed-line...then the VHF radio or GPS installation is the problem...not the fact that I've moved the feed-line.
You mean that thing with all the windows? I guess that's why you can NEVER make a cell phone work when you're in a 150 with the doors closed right?The feed-line is in a shielded box called the fuselage.
Scary.........been putting GPS in A/C since 1989..
Why do you all continue to engage?
WTF!!???
A cable that carries large currents like a generator cable will have a significant electromagnetic field around it.
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