To The Letter

GPS Signals

The "Can GPS Get You Lost?" article in ASL 4/2012 makes some good points. Many pilots have become too dependent on portable GPS receivers and don't even unfold a map let alone follow their track on one. This can mean real trouble if GPS guidance is lost. Several examples in the article, however, leave the impression that GPS signal coverage is an issue, but loss of coverage is extremely rare. Loss of guidance is much more likely due to the limitations of portable units.

GPS signals are very weak when they reach a receiver, making antenna design and location critical. Antennas in portable GPS receivers perform well enough, but not as well as externally-mounted antennas. Airframe shielding can prevent a unit from receiving signals from all available satellites, sometimes resulting in loss of guidance. If this happens, putting the unit up on the glare shield could help, but a pilot's first priority should be to pinpoint position on a map.

Above all, flying the aircraft has to take precedence—too many pilots have been distracted trying to sort out technical problems, with disastrous results. Finding a technical solution can wait until you're back on the ground. This could take the form of a plug-in remote antenna, or in the case of a computer tablet, an external GPS receiver that either uses Bluetooth or connects directly. Another thing to consider with a tablet is whether you can rely on it for maps. In the case of a dead battery or other total failure you will need either paper maps or another electronic map source. 

Regardless of the technical solution, the operational solution is self-evident: fly VFR in weather that allows you to see the ground, follow your track on a map and use your portable GPS receiver as an aid to navigation. 

Ross Bowie
Ottawa, ON

Ross Bowie managed the SatNav Program Office in Transport Canada and then in NAV CANADA for a total of 10 years. After retiring in 2009 he revised the GNSS Manual under contract with the International Civil Aviation Organization (ICAO). He holds an Airline Transport Pilot Licence (ATPL) and has flown for 46 years—the last 20 with GPS.

When the ELT Became the Hazard

A local flight training unit (FTU) requested that I conduct an examination for a private pilot licence on a student pilot in his own Cessna 172 C. I have completed pilot examinations in privately registered aircraft in the past. I insist that the aircraft be inspected by an approved maintenance organization (AMO) to the same standard as a commercially registered aircraft of the same type that may be flown by an FTU. 

While observing Exercise 2D, the pre-flight inspection, I took a notion, for some unknown reason, to personally peer into the aft fuselage behind a panel to see if this aircraft was equipped with a 406 emergency locator transmitter (ELT) beacon or the old style 121.5/243 beacon. To my surprise, the beacon was not where it should have been (attached to the bracket on the side of the fuselage). Upon opening the panel a bit more, I saw the beacon in the belly on its back, still attached to its antenna but lying between the rudder cables and on top of the trim cables. The right rudder cable appeared to have been rubbing on the plastic case of the ELT battery.

I bring this to your attention because the aircraft manufacturer is not required to view this area of the structure during a pre-flight inspection. I think it might be a good idea for owners and operators to assess the safety of any items in such areas periodically. We will never know if my hunch prevented an accident, nor for how long the ELT was in this condition. The commercial and private flight tests do require stalls, sideslips, spirals and/or spins. Therefore, the use of the rudders to recover from these manoeuvres would obviously be of paramount importance.

The owner, in this case, immediately took the aircraft to his AMO, who reinstalled the beacon and also added air to the tires before we boarded the aircraft and conducted the test that day.

John M. Laing
Delta, B.C.

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