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mgh

GPS adversely affects safety

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I read an article on the unintended consequences of GPS on the North Atlantic Tracks (NAT).The general intoduction of GPS has resulted in aircraft following the centre-line of its track very accurately - less than the wingspan of the aircraft. In October 2000 an A340 was cleared to follow Track E at FL360 with an A330 cleared on the same track at FL370 in accordance with the Reduced Vertical Separation Minima (RSVM) Yhe A330 was slowly overtaking the A340 when the A340 was affected by severe wind-shear and began to climb at upto 6000ft/min. This was triggered by the activation of the aircraft's envelop protection system and resulted in an altitude bust of 2400ft. The lateral displacement between the tracks of the aircraft was only 200 ft when the A340 passed through the A330's flight level.Having investigated this incident the CAA recommended that the international bodies consider introducing lateral offsets for aircraft to follow to avoid any re-occurence. So far they haven't, even though the lateral separation between tracks is more than 338000 ft (60nm) while the the vertical separation is 1000 ft!

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6000ft/min! I assume both aircraft had some sort of collision-avoidance proximity warning system though. I know they have GPWS and I assume also they have a system for aircraft......other than the pilot's eyes...Offsets could be the way to go. ALPHA.1 ALPHA.2 etc. each being, say, 5 nm apart along a NAT track called ALPHA.RhettAMD 3700+ (@2585 mhz), eVGA 7800GT 256 (Guru3D 93.71), ASUS A8N-E, PC Power 510 SLI, 2gb Corsair XMS 3-3-3-8 (1T), WD 150 gig 10000rpm Raptor, WD 250gig 7200rpm SATA2, Seagate 120gb 5400 rpm external HD, CoolerMaster Praetorian

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Though there has not been an official report released - it looks like both the Embraer Legacy and the B737 which hit almost head-on over Brazil were both flying exactly on GPS tracks with no offset.Had the Legacy not made an incredible landing, you have to wonder if accident investigators would ever had determined there was a collision.

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Both aircraft received TCAS warnings.According to the invetigation, the A340 entered turbulence which caused fluctuations in pitch angle, normal g, altitude, CAS, N1, and Mach number. The Mach number increased to more than then aircraft's limit of 0.86 M giving a Master Warning (It subsequently peaked at 0.882 M.) The autopilot automatically disengaged, and the thrust levers were closed and cthe autothrottle was disconnected by the handling pilot to keep the speed down. The angle of attack exceeded the 'alpha prot' limit. The system automatically held the incdence at alpha prot limit until the pilot applied forward stick. The aircraft peaked at 15 degree angle of attack. By the time the aircraft reached its highest point (FL384) its speed had fallen to 0.67 M, even though full power had been applied.In a proposal I've seen, aircraft would fly on track at FL300 and 1 nm right for every 1000 ft above and 1 nm left for every 1000 ft below.

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