The following is an html representation of the letter written by Columbus Flight Watch concerning the lack of a backup altimeter setting on numerous instrument approach procedures to airports in the Central Ohio area. For more history on this issue, read an earlier article entitled "I'd Rather RAAS."
January 9, 2001
Dear Central Ohio Airport Manager,
Safety and utility in aviation are built upon the concept of backup systems being immediately available. Due to an effort to reduce clutter on instrument approach charts, the instrument approach procedures (IAPs) into your airport are now without a backup altimeter setting. This has serious implications. It could leave your airport without an approach procedure!
Before your automated weather (AWOS/ASOS) unit was certified, there used to be two sets of minimum altitudes on the IAPs that guided pilots in a safe descent to your airport during poor weather. These alternate minimum altitudes, based on carefully calculated Remote Alternate Altimeter Setting (RAAS) criteria, meant the pilot didn't require your airport's "local" altimeter setting. This option no longer exists. If your "local" (i.e. AWOS/ASOS) altimeter setting is not available, any IAP that is predicated on that altimeter setting is NOT AUTHORIZED.
At an Air Traffic Procedures Advisory Committee (ATPAC) meeting, Mr. Tom Lusch, a member of Columbus Flight Watch and a CMH NATCA Air Traffic Controller, debated that total reliance on a single source altimeter setting is not in the best interest of aviation safety and airport availability. He got his point across. At ATPAC's 100th meeting it was reported that a moratorium has been implemented to prevent future removal of RAAS minima from IAPs. However, it was also learned that RAAS minima will not be re-established for those IAPs already changed, unless requested by the proper authority.
The AWOS/ASOS that serves your airport may have shown itself to be very reliable. However, when it fails, regardless of how well equipped the airplane, without an approved altimeter setting the pilot is immediately left without a legal (and less than safe) means to descend through low clouds or low visibility to land at your airport. For the pilot to be authorized to fly this IAP during a local altimeter setting outage, RAAS minima could be calculated by the Flight Data Center and published via the Notice To Airmen system. However, depending upon the timing of the failure, and its discovery, that could leave your airport without an approved IAP for hours, or even several days.
As the airport manager, you are in a position to change this. We strongly urge you to request the FAA to re-establish RAAS minima and publish them on your IAPs. Also, in the interest of making this as fail-safe as possible, we feel it would be prudent to request that this backup RAAS altimeter be one that is manned 24/7 (i.e. use Port Columbus altimeter setting as a backup for Central Ohio airports).
Sincerely,