Are the big jets safe?

Press, 3 July 1979, Page 19

Are the big jets safe?

H ide-bodied jet airliners, the Boeing 747 jumbos, the DClOs of McDonnell Douglas, and the Lockheed 10'11 TriStars, safely carry many hundreds of thousands of travellers across the nations of the world every day of the week. But none of these makes has a completely accident-free history. This article by a leading British aviation writer, BILL SWEETMAN, of the “Observer," reviews their safety records.

AS THE HORDES of holidaymakers and businessmen prepare to board their flights this week the thought of whether their plane is really safe will be with them as never before.

The DCIO disaster at Chicago has affected travel all over the world. In the United States alone serious defects have been found in 25 grounded planes of the type in which nearly 700 people have died, mainly in two crashes, at Chicago and, in 1974, at Paris. A member of the United States National Transportation Safety Board has said he will never fly in a DCIO again until the whole design has been thoroughly re-vetted. However, there is also reason to look at the way all current airliners are designed, and the way in which their designs are approved for production. The recent discovery of serious structural decay in critical areas of a number of DClOs was the third time in two years that potentially dangerous cracks had been found in planes that, in theory, were too new to be suffering from metal fatigue. The first aircraft to be affected bv this “premature senility” were the Trident Two’s and Three’s of British Airways, which started developing severe wing cracks after individual aircraft had been flying as little as 7000

or 8000 hours. Even on short-range flights, with a consequently large number of landings and take-offs, an aircraft structure should be good for at least 30,000 hours. The Trident problems were discovered before they caused a failure during flight, but they came to light almost by accident: they were not revealed by a scheduled check on the airframe. After being grounded they were allowed to

continue operations only under tight weight, restrictions until major modifications — which included the shortening of the wings —■ were completed. And British Airways were forced to retire the Tridents earlier than had been planned, at considerable cost. While the last of the Tridents were still being modified, another aircraft started showing symptoms of fatigue: the McDonnell Douglas DCB Super 60,

from the same stable as the DCIO. And airframe as failed disastrously at the cracks affected the same area of the Chicago: the junction between the main spars of the. wing and the pylon which carries the engine. Even more significantly, the cracking was confined to two versions of the DCB, the Super 62 and the Super 63. The original DCB was designed in the mid-19505, with engine pylons that wrapped around the leading edge of the wing. (Incidentally, the original DCB has an outstanding reputation for structural durability, requiring far less maintenance than a Boeing 707).

But when Douglas “stretched” the DCB in the mid-19605, they designed a new, much more aerodynamically efficient pylon for the aircraft, and it was this design that suffered from cracking when the Super DCBs had flown for less than half their design lifetimes. The next pylon the McDonnell Douglas team designed was for the DCIO.

The safety of a plane’s structure, including its engine pylons, is not left to theory. One of the first airframes off the production line is placed in a massive nest of hydraulic jacks, known as the “torture rig,” which simulates the loads the aircraft will encounter in service. Before it carries its first passengers, the static “tortured” aircraft, will have completed almost a lifetime of simulated “flights,” compressed into two years.

But the Chicago DCIO had flown only 19,000 hours of a designed 80,000-hour life; severe cracks have also been found in DClOs that were little older. The oldest DCIO has flown only 25,000 hours* since the type was introduced in 1971. As with the Trident and Super DCB, highly localised and excessive stress was neither predicted by theory nor accurately simulated by structural tests. Hence the rapid move by the United States Federal Aviation Administration to review the design of the pylons on the other big jets — the Boeing 747, Lockheed TriStar and Airbus A3OO. There but for fortune go you, suggests the F.A.A., although Boeing was notably quick to state that it had no worries about its aircraft. Once the wide-body jets entered service it was inevitable that sooner or later one of them would crash with a full load of passengers on board. It duly happened on March 3, 1974, when a Turkish Airways DCIO, of the same type as the one at Chicago, crashed just outside Paris, killing 346 people. That it took four years to happen was remarkable: it was a far better record in terms of fatal accidents per mile flown than the early jets achieved. After the crash, however, it emerged that the accident had been caused by a mechanical failure of a freight .door, a failure that had nearly destroyed an American Airlines DCIO more than a year before. The modification intended to prevent repetition had not been applied to the aircraft that crashed at Paris, nor to a number of other DClOs in service throughout the world. It had been recommended by the manufacturer but

never made compulsory by the Federal Aviation Administration. Many of the attacks made on McDonnell Douglas and the F.A.A. were overstated, but the American Airlines incident and the Paris crash constituted the worst failure of the air-safety system for years.

Technically, of course, the Paris and Chicago crashes are totally unrelated. But connection will inevitably he made in the public mind. All three of the United States widecabin jets—the four-engined Boeing 747 and the three-engined DCIO and Lockheed TriStar—have been designed, certified and operated according to Federal Aviation Administration rules. None of them has had an accident-free career, but all have avoided the phenomenon of “introductory accidents” that plagued the earlier jets. So far eight Boeing 7475, six DClOs and two TriStars have been reported wrecked and written-off. The 747 has flown many more hours than the DCIO. and the DCIO is even further ahead of the TriStar, with more than twice as many hours in the air. But while the DCIO and TriStar operate on similar route systems, the 747 flies longer distances, so it spends proportionately less time in the critical areas of land and take-off than the others. Of the eight 747 losses, two were caused by the action of terrorists who blew the aircraft up on the ground. One of the two TriStars lost was accidentally burned out on the ground, apparently bv a cleaner’s cigarette. It can be taken" that the type of aircraft was irrelevant to the cause and results of those accidents. Collision at Tenerife Two more 747 s lost were destroyed in the Tenerife collision in March 1977; here again, it is hard to blame the accident on the design of the aircraft. The cause of an Iranian Air Force 747 crash near Madrid was almost certainly the result of the aircraft being struck by lightning, which ignited residues of JP-4 fuel in the wing: the combination of lightning and JP-4, generally considered too dangerous for airline use, would destroy any aircraft.The root cause of Chicago has yet to be determined, but as at Paris, the investigation will probably lead to the permanent modification of the aircraft or inspection procedures. So far, the National Transportation Safety Board investigators have traced the problem to the pylon/wing junction.” The Los Angeles accident in March of last year has also made its mark in the airline world. A DCIO was running up for takeoff when two of the tyres burst. The aircraft was not going fast enough for the take-off to be continued safely, and the pilot decided to abort.

According to the McDonnell Douglas/ F.A.A. manual, there should have been room for a safe deceleration, but the failed tyres caused the aircraft to slew off the runway. One undercarriage leg, instead of failing cleanly as it was designed to do, tore away from its mountings and ruptured the fuel tanks. Two passengers were killed in the resulting fire; the aircraft was destroyed. This accident was similar in some ways to the crash of an Overseas National Airways DCIO at New York Kennedy Airport in November 1975; there, too, the aircraft, was destroyed following an aborted take-off. No other wide-body aircraft have been destroyed in similar circumstances, although tyre-bursts are a persistent problem at high weights and high temperatures. There have, however, been no comparative studies of the runway stability of the three main wide-body aircraft. The other two DC 10 losses listed also appear to have had some similarities. The aircraft at Boston and Istanbul both landed short of the runway. In none of the DCIO accidents mentioned can the characteristics of the aircraft be as confidently excluded from the causes of the loss of the aircraft as in the case of all but three 747 losses and all but one TriStar loss. After well over 10 million flying hours on the three United States wide body jets, can it still be confidently classified as bad luck?

* Three of Air New Zealand’s fleet of eight DClOs. which unlike the ' aircraft that crashed at Chicago are all of the series 30 model, have flown more than 20,000 hours. The oldest aircraft has flown 26,700 hours.

* Since this article was written. Investigators have also expressed concern about the absence of a braking system that would stop the leading-edge slats from retracting in the event of a hydraulic failure such as reportedly occurred when the engine broke aivay from the wing of the Chicago aircraft.