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TRANSPORTAIRCRAFTTECHNICALSERVICESCOMPANY,INC.
2343 Estate Gate Drive-  San Antonio, Texas 78260
Phone 830-438-3817-Facsimile 830-438-3816
e-mail tatsco@tatsco.com
WEB SITE http:// www:tatsco.com

An Aircraft Remarketing Services Company
Providing Technical and Remarketing Services Since 1974
Serving as an FAA Designated Airworthiness Representative Since 1983

***** NEWSLETTER *****
AUGUST 22, 2000
VOLUME 18 - ISSUE 8, pages 2-3

"THE SHORT MEMORY . . . .On March 31, 1986, a Mexicana Airlines Boeing 727-200 took off at 8:40 a.m. from Mexico City heading to Los Angeles. At 9:05 a.m. the pilot radioed Mexico City air traffic controllers "Emergency! Mexican 940 requests a return to Mexico City." The 727 crashed shortly afterwards into the side of a mountain about 100 miles northwest of Mexico City killing all 166 passengers and crew on board. It was determined the aircraft was destroyed by a blowout of one of the tires. The tire had ruptured fuel, hydraulic and electrical lines as well as air-conditioning ducts that were near the wheel well. The aircraft had been modified for use as an extended range aircraft, and given the conventional fuselage. s confined spacing, the additional fuel tanks were also placed in the aft cargo compartment just aft of the wheel wells. (Airworthiness Directive 87-08-09 was issued the following year. This A/D requires that tires on wheels with brakes installed [the brake overheating causes the tire pressure to increase until the tire or wheel fails] to be serviced with NITROGEN-which will suppress any fire caused by overheating.) Unlike many, if not all 747 Classic Series, the 727 does not have brake temperature monitoring gages on the flight engineer. s panel.

TWA 800 . . . . A TIRE FAILURE?The wing mounted main landing gears on the 747 are in close proximity to the aft wing spar (also known as the rear wall of thecenter wing tank). A tire failure could cause the same problem experienced by Mexicana. One of the right gear wheels, located closest to the wing spar on TWA 800, was missing its tire.

WHAT HAPPENS WHEN A TIRE EXPLODES?Air Safety Week had an interesting article on the energy released by exploding tires in their August 7, 2000 issue. It was addressing the tire failure on the Concord. If you go to page 3 you will find a chart-Energy Released by Catastrophic Tire Deflations. If you "used the same numbers" for a P-3 (Navy aircraft) main landing gear tire at 200 pounds per square inch (psi) tire pressure to approximate the energy released by a 747 main landing gear tire failure (194 psi)-it would be301,071 foot pounds. . . . equal to 0.60 sticks of dynamite.If the tire burst at the maximum pressure of 1,170 psi it would release 1,215,789 foot pounds of energy-an amount equal to 4.4 sticks of dynamite. NOTE: According to an article in the August 26th, 1996 issue of Aviation Week & Space Technology, one of the landing gear bogies was heavily damaged.

TWA 800-REAR SPAR DAMAGE . . . . (From NTSB Exhibit 7 A-Structures)

A section containing a portion of the web from LBL 11 to RBL 33 at the upper spar chord and LBL 19 to BL O at 10" above the lower chord suffered damage on the entire periphery of the web, with the edges bent both forward and aft. The lower portion of the web was bent forward approximately 180 degrees. The CWS scavenge pump is not attached to the spacer plate or the spare web [it was not found]. The mounting spacer plate for the CWS fuel scavenge pump remained in place on the aft side of the rear spar, but it had been deformed away from the spar web except at the 9-11 o. clock position. The three bolts that mount the spacer to the spar web were in place and the safety wires were still attached. There was a partially sooted outline of the pump housing on the spacer plate and a difference in soot levels on the forward side of the spar web where the pump is mounted as compared with the remainder of the web. There is only a very light soot deposit on the spar web where the spacer plate has been deformed from the web. The forward side of the lower portion of the web that is bent up 180 degrees has a location that shows impact damage to the web and to the fillet seals on the fastener heads. This section shows heavy soot and fire damage on not only the forward and aft surfaces but also on the web and stiffener fracture edges. It also shows marked difference of soot levels as compared with the adjacent segments. The stiffener to web interface at LBL 11 shows both sooted and unsooted regions on the interface where the stiffener is missing. The protruding portion of the fasteners that have failed also show soot accumulation.(See Fire and Explosion group notes for details of the sooting and fire damage). Two segments of the rear spar remained attached to stiffeners that remained attached to the keel beam box.

INTERNAL SIGNS . . . .The damaged center tank span wise beams (SWB) described in Exhibit 7A appear to indicate two areas of high pressure-between the front wing spar and SWBs 3 and 2 (the lower flanges of the front spar and SWB 3 are distorted forward and the lower flanges of SWB 2 and the mid-spar are distorted aft)-the other area is aft of the mid spar (SWB 1 and the rear spar show distortion both forward and aft). (SWBs are numbered from rear to front.) There is "interesting damage" between the mid-spar and the aft spar . . . .

There is a puncture in the skin panel 6 inches forward of SWB 1 at LBL 37 with the surrounding skin bent down. The right end of this section has the general shape of an upward deflected dome that is as high as 14 inches in relation to the adjacent structure. The dome is centered about RBL 57.5 between S-8 and S-9.

IF IT WASN. T A TIRE FAILURE WHAT COULD IT HAVE BEEN (I can speculate-the NTSB can't.)One of the theories I presented during an interview on the NBC NightLine program a month after the accident was the igniting of vapors in the center wing tank (CWT) by the aircraft galleys. An early news article stated that damage to a passenger seat just aft of the galley may have been caused by an explosive under the seat.

If you searchthe FAA Service Difficulty Report (SDR) database you will find several reports of in flight fuel vapors-both in the cockpit and the passenger cabin (DURING CLIMB FUEL FUMES WERE DETECTED NEAR ROW 20). Airworthiness Directive 90-11-08-B747-200 Front Spar fuel leaks-has two inspection area requirements. The front spar inspection does not pertain to the 747-100 but the second inspection, the upper wing skin of the CWT, for proper application of the secondary fuel barrier is relevant. The sealant is applied during production but it could have been removed during corrosion removal (the upper wing skin is a "popular area" for corrosion).

Now . . . .Go back to the SDRs and search for B747 Galley Oven Failures. Arcing and open flames are common malfunctions (I seem to recall one of the SDRs pertained to an oven on this aircraft).

And . . . .What do the flight attendants do shortly after an evening departure from JFK (to Europe)? Turn on the ovens to preheat them for dinner.

BOEING FLEET STATISTICS . . . . . THE TOTAL BOEING FLEET HAS, THRU 03/31/2000, FLOWN 353,328,934 HOURS AND ACCUMULATED 207,650,683 LANDINGS. THERE ARE 8,253 ACTIVE AIRPLANES. THE HIGH TIME (HOURS) AIRCRAFT IS A MODEL 747-200F OPERATED BY KOREAN AIRLINES. IT HAS FLOWN MORE THAN 115,000 HOURS. THE HIGHEST LANDING AIRCRAFT IS A FORMER USAir 737-200 WHICH HAS ACCUMULATED MORE THAN 96,000.

FUEL TANK WIRING . . . . MOST OF THE BOEING-CLASSIC SERIES-AIRCRAFT HAVE THE SAME DESIGN FUEL QUANTITY MEASURING SYSTEM (FQMS).We estimate these aircraft have flown in excess of350 million hours and 200 million landings without evidence of a fuel tank fire or explosion caused by faulty wiring. "

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