Boeing 757: A Modern Classic
The airplane Boeing got just right. //

The bigger story here, I think, is the decline of Boeing’s reputation for engineering excellence since its 1997 merger with McDonnell Douglas. Since the merger, not one but two new Boeing airliners have been grounded by the FAA, the first such groundings since McDonnell Douglas’ own DC-10 in 1979. The Boeing 787, while a fine design, has suffered many quality- control problems stemming from a complex outsourcing scheme that only an MBA could love, and a union-busting move to South Carolina, bypassing the experienced and costly Seattle workforce. The most serious flaw was a subcontractor’s defective lithium-ion batteries that were prone to thermal runaway and fire, an eventuality that Boeing (and the FAA) failed to predict and mitigate. //

Rather than kick Boeing any more while they’re down, I think it might be instructive to take a look at one of the best airplanes built by the “old” Boeing (or indeed, any manufacturer anywhere), an airplane I’ve come to regard with great respect and affection over the past several years of flying it. I’m speaking, of course, of the venerable Boeing 757. For decades, Boeing’s reputation largely rested on four excellent designs: the 747, 757, 767 and 777. Of these, the 757 has enjoyed the longest success without any significant redesign because Boeing engineers got the plane exactly right on the first go. Even today, as the 757 fleet ages, the airlines haven’t been able to find anything to replace it; there’s still no modern design that performs its mission as well as it does, and so it soldiers on in the fleets of all three U.S. legacy carriers and many overseas airlines as well. //

The 7N7 and 7X7 programs ended up becoming quite enmeshed, as they incorporated the same new technologies, and eventually achieved enough flight deck and systems commonality to be awarded a common pilot type rating despite significant differences in size and handling characteristics. The two designs entered service within months of each other in 1982 as the 757 and 767, respectively. Sales of the 757 were slow at first but took off in the late 1980s and stayed steady through the ’90s before abruptly tapering off after 9/11. Production ended in 2005 with 1,049 aircraft built; nearly 70 percent of the fleet is still in service today, 37 years after the type was first delivered. //

At 240,000 pounds max takeoff weight and 77,000 to 80,000 pounds of thrust depending on the engine option (Pratt & Whitney PW2037 or Rolls-Royce RB211), the 757-200 has the highest thrust-to-weight ratio of any airliner except Concorde. //

The plane’s real strength, however, is its ability to make a 2,200 nm transcontinental flight (say, Boston to San Diego) with an alternate a few hundred miles away and ample reserves, haul an absolutely full load of passengers and cargo, and still take off from a 7000-foot runway and climb straight into the mid-30s. Nothing else can do that, neither the A321 nor the 737-900ER, though the airlines have tried. That’s why the 757 is still popular after all these years.

Abstract

Ten polymeric materials including EPDM, Nylon 6,6, Buna-N and other materials marketed* as TFE-Teflon® (PTFE), Kel-F® 81 (PCTFE), Vespel® SP-21, Viton® A, Viton® A-500, Fluorel®, and Neoprene® were systematically evaluated for their oxygen compatibility property. The specific properties examined included: (1) autoignition temperature (AIT), (2) heat of combustion, and (3) liquid-oxygen (LOX) mechanical impact sensitivity. Test methods and procedures employed for the evaluations were in compliance with those prescribed in the ASTM and BSI standards. Additionally, a BOC in-house high-pressure autoigniticn test rig (HP-AIT) was used for a detailed study on the materials' autoignition behavior. This high-pressure vessel is capable of probing the AIT of a material up to 450°C and at oxygen pressure (prior to a thermal excursion) up to 5000 psig (∼34.5 MPa).

According to the test results, fluorinated polymers including TFE®, Kel-F® 81, Viton® A, Viton® A-500 and Fluorel® exhibited superior oxygen compatibility property. Specifically, they possessed relatively high autoignition temperatures and reasonably low heat of combustion values. Among them, TFE® possessed the best property by showing the highest autoignition temperature (>450°C), lowest heat of combustion (1517 cal/g), and qualified (pass) LOX impact sensitivity. Vespel® SP-21 (15% graphite-filled polyimide) exhibited an autoignition temperature higher than fluorinated elastomers like Fluorel® and Viton® A, but lower than Kel-F® 81 as well as TFE®. The variation of oxygen pressure, ranging from 1800 psig (∼12.4 MPa) to 5000 psig (∼34.5 MPa), was found to exert little influence on the autoignition temperature of the polymers.

The autoignition behavior of Kel-F®81, Viton® A, Vespel® SP-21, and Nylon 6,6 was further investigated, using HP-AIT, as a function of sample quantity and surface area at different oxygen pressure. On the one hand, variation of sample quantity exerted a more pronounced effect on the AITs of Viton® A, Nylon 6,6 and Kel-F® 81 at various pressures than on Vespel® SP-21. A higher autoignition temperature was generally observed from samples with smaller quantities. On the other hand, changes in sample surface area had little influence on the autoignition temperature of the materials in 1800 psig (∼12.4 MPa) oxygen.

Recent studies show vaccines for mumps, pertussis, meningococcal disease, and yellow fever also lose their effectiveness faster than official immunization recommendations suggest. Vaccines have been a crucial public health tool for decades, so it may seem strange that their durability isn't well understood. But vaccines are approved and come to market years before it's clear how long protection lasts. Later, fading protection can go unnoticed because a vaccine in wide use has largely eliminated transmission of the microbes it protects against, making "breakthrough" infections rare. Even if viruses or bacteria are still in circulation, people vaccinated against them will sometimes receive natural boosting of their immunity. And declining vaccine immunity is not an all-or-nothing phenomenon: A breakthrough infection often leads to much less severe symptoms of the disease.

Researchers are ramping up efforts to figure out why some vaccines protect for mere weeks but others work for life. "We simply don't know what the rules are to inducing long-lasting immunity," says Plotkin, who began to research vaccines in 1957. "For years, we were making vaccines without a really deep knowledge of immunology. Everything of course depends on immunologic memory, and we have not systematically measured it."