Doug Kerr
Well-known member
I read that in the US the Federal Aviation Administration has relaxed the rules on the use of electronic devices in flight such that many devices can be used "gate-to-gate", and some can still only be used above 10,000 feet elevation.
Cellular telephones, however, still cannot be used in flight at all. Some may feel that this is a strange limit. Often in the past people have said, "I can't believe that there would really be interference between cellular telephone emissions and navigational systems. They each operate in clearly separate frequency bands, and spurious emissions are tightly controlled. This restriction must be some kind of conspiracy against travelers."
Well, the technical part of that observation is actually apt. In fact, the original prohibition against the use of cellular telephones in flight was only in small part based on concern with potential interference with navigational systems, and is origin was with the FCC, not the FAA.
The principal issue as (and still is) that, based on the design concept of cellular networks, an airborne cellular telephone can wreak operational havoc on the network itself.
The original cellular concept was predicated on the fact that when a cellular telephone sends out an origination request message to request a channel over which to place a call, a usable signal would only be received by base stations in one, or at worst several adjacent, systems.
Because all the base stations in one systems are under common management, and there is coordination of one sort or another between adjacent systems, that would result in only one of those base stations responding to the telephone, giving it an initial channel assignment.
But if a telephone at an altitude of 30,000 feet sends an origination request message, it might be received by several base stations in the Cleveland system, and several in the Columbus system, and several elsewhere, and one from each system might respond to the telephone (totally unbeknownst to the other system). The result is not pretty.
Sophisticated aspects of modern cellular system and intersystem protocols mitigate this phenomenon somewhat, but it still is a major consideration.
Best regards,
Doug
Cellular telephones, however, still cannot be used in flight at all. Some may feel that this is a strange limit. Often in the past people have said, "I can't believe that there would really be interference between cellular telephone emissions and navigational systems. They each operate in clearly separate frequency bands, and spurious emissions are tightly controlled. This restriction must be some kind of conspiracy against travelers."
Well, the technical part of that observation is actually apt. In fact, the original prohibition against the use of cellular telephones in flight was only in small part based on concern with potential interference with navigational systems, and is origin was with the FCC, not the FAA.
The principal issue as (and still is) that, based on the design concept of cellular networks, an airborne cellular telephone can wreak operational havoc on the network itself.
The original cellular concept was predicated on the fact that when a cellular telephone sends out an origination request message to request a channel over which to place a call, a usable signal would only be received by base stations in one, or at worst several adjacent, systems.
Because all the base stations in one systems are under common management, and there is coordination of one sort or another between adjacent systems, that would result in only one of those base stations responding to the telephone, giving it an initial channel assignment.
But if a telephone at an altitude of 30,000 feet sends an origination request message, it might be received by several base stations in the Cleveland system, and several in the Columbus system, and several elsewhere, and one from each system might respond to the telephone (totally unbeknownst to the other system). The result is not pretty.
Sophisticated aspects of modern cellular system and intersystem protocols mitigate this phenomenon somewhat, but it still is a major consideration.
Best regards,
Doug