Hot Coffee And GPS Coverage

Many of our daily activities are aided by the coverage of GPS satellites providing many of our devices with a precise location. It is really convenient when traveling in an unfamiliar city to quickly locate a coffee shop for that morning cup of joe. The inconvenience quickly becomes edgy when our navigation device can’t locate itself due to poor satellite reception causing a delay in our caffeine consumption.

However, it is much more disruptive when our RNAV system in the flight deck lacks satellite reception and we are limited to navigate using traditional Class I methods. Generally, the coverage of Global Navigation Satellite Systems (GNSS) around the globe is very good and a high level of reliability can be expected. But every once in a while, usually when we have a trip scheduled at the same time, a GPS outage occurs that requires us to make some adjustments.

Such is the case along the Eastern coast of Florida recently. GPS NOTAMs have highlighted a large swath of area for several days that will be in the shadows of the orbiting satellites. During your flight planning, that T-Route or Q-route which would have straightened your route is no longer reasonable to file. Is the wind favoring an approach to a runway that only has an RNAV (GPS) instrument approach, that might cause an issue at your time of arrival? What type of downgraded functions will your autoflight system revert to?

The good news is that hot coffee can be brought with us in the aircraft, which will be helpful in reviewing the available GPS NOTAMs and deciding how to handle these downgrade issues. Flight crews may use the following sources to review the GPS NOTAMS:

• Service Availability Prediction Tool (SAPT)
• 1-800-WXBRIEF: You'll need to specifically ask for GPS NOTAMS from the person briefing you. FSSs do not provide RAIM prediction as part of a standard briefing.

You can complete a thorough review of this and other RNAV topics in Advanced Aircrew Academy’s RNAV PBN eLearning module.