Adhemar a écrit :Si on te demande d'éteindre ton gsm (et pas seulement d'envoyer des messages), c'est peut être qu'il y a aussi un risque que tu reçoive un appel,non ?
Lil'Shao a écrit :...Et ici on ne parle pas de sms, mais d'appels, parfois durant plusieurs minutes, d'avions en altitude.
Nous parlons du vol 93 et la plupart des appels n'ont pas dépassé 1 minute (voir plus bas).
Quant à l'
altitude comme tu dis...doucement les basses car
perdre de l'altitude avec ce type d'appareil prend du temps...et les pirates devaient être en mesure d'adopter un taux de descente qui les amenaient à proximité de leur cible rapidement. Il est peu probable qu'ils aient songé à un référendum pour décider de la trajectoire puisqu'ils étaient susceptibles d'être pris en chasse par des F-16. Certains prétendent d'ailleurs que le vol 93 a été descendu par un missile tiré d'un chasseur. Je n'ai pas examiné le tout et suis par conséquent incapable d'émettre une opinion à ce sujet.
Lil'Shao a écrit :Pour l'avoir laissé allumer plusieurs fois en avion je sais que le réseau disparait assez rapidement apres le décollage...
Assez rapidement hein ? Essayons de voir ça de plus près...
Les vols que tu as empruntés étaient des vols réguliers.
Rappelons que jusqu'à 10,000 pieds, il est interdit aux vols commerciaux de
dépasser la vitesse de 250 noeuds.
The rules you most need to know
How fast can you go (FAR 91.117)?
Below 10,000 feet MSL, aircraft are to slow to 250 knots indicated airspeed. This speed may also be used inside Class B airspace. Once below 2,500 feet above the surface, and within four nautical miles of the primary airport in a Class C or D airspace, the aircraft must be slowed to 200 knots. When you are flying under Class B airspace or when in a VFR corridor through Class B airspace, the indicated airspeed must be 200 knots or less. If an aircraft's minimum safe speeds are higher than allowed in the regulations--such as is the case with the Concorde or Boeing 747--then the aircraft may be flown at minimum safe speeds.
D'après un rapport, la plupart des appels du vol 93 n'ont pas dépassé
1 minute. Brenda Raney de Verizon Wireless - voir plus bas - mentionne également ce fait.
Et elle ajoute:
Brenda Raney a écrit :It helped that the planes were flying in areas with plenty of cell sites, too. Even United Airlines flight 93, which crashed in rural Pennsylvania, was supported by several nearby cell sites
Rappel: 1 noeud = 1852 m = 1.852 Km
La distance parcourue en 1 minute par un avion volant à 250 noeuds est de (250*1.852/60) = 7.716 Km
Que les vilains pirates aient osé désobéir au contrôleur en volant à 400 noeuds ne change pas grand chose à l'affaire: (400*1.852/60) = 12.346 Km à la minute.
Rien d'extraordinaire.
La couverture peut se dégrader "assez rapidement" certes, mais l'expression "assez rapidement" est ambigüe et essentiellement subjective.
C'est surtout la "couverture" du pifomètre qui se dégrade rapidement.
Voici quelques extraits de textes pertinents:
Tout d'abord
ce lien
Some of the conversations were WITH ONBOARD AIR PHONES, WHICH CONTRARY TO THE CELL PHONES PROVIDE FOR GOOD QUALITY TRANSMISSION. The report does not draw a clear demarcation between the two types of calls.
Autre extrait
Because wireless networks are designed for terrestrial use, the fact that so many people were able to call from the sky brings into question how the phones worked from such altitudes.
Alexa Graf, AT&T spokesperson, said systems are not designed for calls from high altitudes, suggesting it was almost a fluke that the calls reached their destinations.
“On land, we have antenna sectors that point in three directions — say north, southwest, and southeast,” she explained. “Those signals are radiating across the land, and those signals do go up, too, due to leakage.”
From high altitudes, the call quality is not very good, and most callers will experience drops. Although calls are not reliable, callers can pick up and hold calls for a little while below a certain altitude, she added.
Brenda Raney, Verizon Wireless spokesperson, said that RF signals actually can broadcast fairly high. On Sept. 11, the planes WERE FLYING LOW WHEN PEOPLE STARTED USING THEIR PHONES. AND, EACH CALL LASTED 60 SECONDS OR LESS.
“They also were digital phones, and there's a little bit more leeway on those digital phones, so it worked,” she said.
It helped that the planes were flying in areas with plenty of cell sites, too. Even United Airlines flight 93, which crashed in rural Pennsylvania, was supported by several nearby cell sites, Raney added.
Despite the numerous calls from wireless phones, it was the hijackers — not interference with the airplane's operating system — that brought the four planes down. Many in the wireless industry question whether wireless devices cause problems on board aircraft after all.
“With air travel, you want to take every precaution you can, but my understanding is that not calling from planes is a bit of a precaution,” Graf said.
Keith Nowak, Nokia media relations manager, agreed.
“In reality, a cell phone could cause a warning light not to work, but it wouldn't be anything serious. There's the potential to cause some effects, but it's generally a preventative measure.”
He who thinks by the inch and talks by the yard deserves to be kicked by the foot. (Proverbe chinois)
