Sunday, February 14, 2010

Part 5 Integrity and Current World GPS status

The integrity of any radio signal a pilot uses may be more important than the accuracy of the signal.  As we operate in a "safety of life" enviornment it is imperative we become aware as soon as possible when ever the signal becomes unreliable or is  lost.

Prior to augmented GPS signals being available, we relied upon the GPS receivers built in Receiver Autonomous and Integrity Monitoring (RAIM) and Fault Detection and Exclusion (FDE) to supply warnings.  These warning may take as long as 10 minutes before it is delivered to the pilot.  This is not acceptable for most of our operations.

Both Ground Based Augmentation Systems (GBAS) and Satellite Based Augmentation Systems (SBAS) are able to warn the pilot with almost no time delay. It should be clearly apparent to the pilot the superior advantage of having an augmented signal. As the WAAS capability does not add to the cost of the receiver, I am astonished how few corporate aircraft are equipped with it.

Many older airliners are still not equipped with GPS, let alone WAAS GPS as there is no regulatory requirement to do so. The superiority of the GPS signal to provide navigational information should insure that it is installed on all aircraft. The increased integrity of the augmented signal along with the increased accuracy also should insure it is installed on all aircraft.

I have been suggesting that all pilots carry their own personal battery powered portable GPS receiver to cover the possibility of encountering an event where the loss of the aircraft's GPS receiver happens. A GPS has the ability to deliver us aircraft ground speed. In the event of the loss of pitot and static instruments or loss of indicated airspeed information, you can apply and wind speed estimate and use the ground speed as a substitute for indicated air speed.

If the GPS receiver has at least 4 satellites in view, it will calculate our altitude giving us a chance to substitute for our altimeters.  The GPS will also calculate the aircraft track angle and update that information at least once per second.  This will permit us to use the GPS for turn information as well.

Have you ever viewed the GPS calculated altitude in your aircraft?  Does the Flight Management System (FMS) on your aircraft permit you to view the GPS calculated altitude?  Most FMS systems will allow you to view it on the sensors page but some older units do not allow it. Assure your self you have the ability to view it and you know how to access it.

Back in 1996, an Aero Peru Boeing 757 with 75 crew members and passengers took off at night in Instrument Meteorlogical Conditions (IMC) over water with duct tape covering the pitot and static ports. The crew suffered from unreliable incorrect instrument indication as well as numerous aural warnings and warning lights.  The resulting confusion of the flight crew ended 30 minutes later when the aircraft stalled and crashed into the water with all on board killed.

If the crew had available a portable GPS receiver , they would have had enough information to avoid stalling the aircraft and would be alive today. Do you carry a portable GPS receiver on board your aircraft today?

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