Date: 201404
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Weather elements / visibility: VFR; 20
Aircraft: Skyhawk 172/Cutlass 172
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Final Approach
Airspace: Class E ZZZ
ATC / advisory: UNICOM ZZZ
Aircraft component: GPS & Other Satellite Navigation
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Private
Human factors: Human-Machine Interface
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Manuals; Human Factors
Primary problem: Aircraft

Narrative: The aircraft was a Cessna 172 equipped with a Garmin 430w (WAAS) Enroute/approach GPS. My personal 'SPOT' Satellite tracker/messenger device was turned on and placed on the aircraft's dash.While performing practice instrument GPS approaches under the hood with a flight instructor as a check pilot. The Garmin 430w failed with an integrity alarm after the final approach fix and in the LPV mode four consecutive times. Only after the SPOT device was turned off and batteries removed was I able to make GPS instrument approaches down to minimums without incident.I am very concerned about this as many other pilots use the SPOT tracker/messenger device. The fact that SPOT device clearly interfered and failed the Garmin 430w GPS on final is extremely worrisome. Had this happened during real IMC and I had not the caught the GPS failure I could have flown the plane into the ground.  There are many new electronic devices on the market and pilots may not be aware of the dangers with them.  Furthermore; with the FAA allowing all electronic devices to be turned on during commercial aircraft I am concerned that if a passenger turned on a SPOT device during flight it could interfere with the GPS system on a commercial airliner.

Callback: The reporter advised he was unaware whether it was necessary to remove the batteries from the SPOT device to eliminate the interference. He did so because it is necessary to hold a button for specific period of time to turn it off and there was no obvious optical indication of actual status. As a result he removed the batteries to insure it was deactivated.Since the event he has reviewed the SPOT operator's manual and discovered there is an admonition to not have the device in close proximity to other GPS devices when both are in use as there is a potential for the interference he experienced and for which the Integrity Warning was issued.  He did not recall a specified proximity within which such interference was likely.The reporter also made a somewhat unrelated comment that is generically pertinent to the operation of GPS/FMS equipped General Aviation aircraft; particularly those available for rent from FBOs.  He had recently suffered an altitude excursion event in a different C172 equipped with a touchscreen interface; a type he had never utilized before.  While in IMC; with light to occasional moderate turbulence; the effort necessary to program the touchscreen for the ensuing approach so diverted his attention for a long enough period of time to have lost over a thousand feet of altitude.  He believes that the operational differences between the various glass nav avionic systems presents a significant challenge to users of rental aircraft.  Differences far beyond those encountered in the days of a VOR tuning knob and its associated FPDI course knob.



Synopsis: The pilot of a C172 shooting practice RNAV (GPS) approaches encountered four instances of his Garmin 430x GPS failing and producing an integrity alarm inside of the FAF. Only after turning off and removing the batteries from his SPOT Satellite Tracker/Messenger device did the GPS provide continuous reliable navigation.