Weakest points

This story is sourced from Flight International
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While airline accidents worldwide are continuing their downward trend, they serve to highlight those regions and business sectors where safety is still an issue

Airline accident figures for the first half of this year show that, despite the uninterrupted gentle trend toward improvement, there is still stark evidence of carelessness in some sectors of the aviation community. Cargo operations, turboprop operators and third-world countries’ airlines are all proving resistant to the industry’s largely successful attempt to push for a commercial aviation environment free of serious accidents.

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The lowest number of airline fatal accidents in the first six months of each year of the last decade was in 2003. There were 12 fatal accidents then, according to Flight International’s review of world airline safety for the first half of each year. That figure rose to 14 for the same period last year and 16 in the six months to 30 June this year; but at the same time the total number of fatalities has continued downward (see graph), reflecting the higher proportion of accidents involving small aircraft and cargo operations .

Controlled flight into terrain (CFIT) accidents have returned, points out Flight Safety Foundation (FSF) director of technical programmes Jim Burin, observing that the industry had been free of jet accidents in that category since June 2003. This year a Kam Air Boeing 737-200 hit high terrain while it was climbing away from a go-around in poor weather at Kabul, Afghanistan. Citing two recent turboprop aircraft CFIT accidents – the October 2004 Corporate Airlines BAe Jetstream 31 at Kirksville, Missouri, USA and the 7 May Aero Tropics Fairchild Metro crash in Australia  – Burin points out that they were both scheduled to be fitted with terrain awareness and warning systems (TAWS). It remains true that no aircraft of any type fitted with a TAWS has suffered a CFIT accident in the seven years since it became common practice for airlines to fit the system. International Civil Aviation Organisation standards and recommended practices say that TAWS should be mandated, but most countries are being slow to implement the requirement. That North America, Europe and Australasia and individual countries in other regions have mandated TAWS and it is fitted as standard to all new commercial aircraft means that almost half the world’s fleet is TAWS-equipped, reducing the frequency of CFIT crashes generally and confining them to the non-equipped fleet in particular. Non-TAWS turboprops accounted for three of the five CFIT accidents this year to the end of June, and at least one of the accidents in the “unknown” causal category (see pie chart) may well turn out to be the same.

Burin notes that there has been a higher than usual proportion of turboprop fatal accidents and hull losses. One of the characteristics of turboprop serious accidents is that, unlike jet accidents, not only do they occur in states with poor safety oversight, they frequently still happen in countries that have a good safety culture and in which big-jet accidents have more or less been eliminated. It seems to be one of the remaining weak points in the air transport world’s largely successful campaign to improve safety performance.

The Aero Tropics Metro accident was the worst – in terms of loss of life – in Australia for more than 40 years. The USA has seen one turboprop accident this year so far – last year there were four; and New Zealand has also lost a Metro, apparently due to structural failure in flight. One aviation analyst who does not wish to be named says that many turboprop operations are, by their nature, flown by small carriers that work to legal minima and do not nominate a safety manager.

A pair of factors that has come together in several fatal accidents already this year is the apparently risky combination of the African operating environment and veteran Soviet-built aircraft. In Africa this year so far there have been fatal accidents involving two Antonov An-12s, one An-24, and two Ilyushin Il-76s. Meanwhile Lake Victoria has become a frequent final destination for old freighters – not always fatally, but the aircraft never fly again. This year there has been a fatal Il-76 crash (23 March) into Lake Victoria just after take-off from Mwanza, Tanzania, on the lake’s southern shore, and a non-fatal Boeing 707 crash (19 March) on the approach to Entebbe, Uganda, on the northern shore. In February 2000 at Mwanza a Trans Arabian Air Transport 707 crashed into the lake – again on approach; but in April the same year a DAS Air McDonnell Douglas DC-10-30F freighter ran off the end of Entebbe’s runway into the lake.

The two Western-built jets involved in fatal crashes this year were first-generation (707) or second-generation (737-200) jet airliners. There have been no accidents involving third- or fourth-generation jets so far. Meanwhile, more than half the jet hull-loss accidents in the past 12 months have occurred during the approach and landing phase, observes Burin, despite the FSF’s long-standing approach and landing accident reduction research programme and awareness campaign.

Rudder separation

Among the non-fatal incidents this year so far there are several that confound intelligent speculation as to their cause. At the head of the list is the 6 March Air Transat Airbus A310-300 rudder separation. The composite rudder did not separate at the hinges but the structure of the rudder appears to have failed, leaving practically no usable rudder surface still attached. The aircraft returned to Varadero, Cuba where it had taken off, and landed safely after a surprisingly stable return flight considering the almost total rudder loss. All that is known from the early investigation by the Transportation Safety Board of Canada is that the crew had not manipulated the rudder abnormally, nor had it undergone the stress of an uncommanded deflection, and it did not have a record of being damaged before the incident.

There is no previous record of an aircraft composite primary structure or control surface having failed unless it had been considerably overloaded, as in the case of the American Airlines AA587 accident involving an Airbus A300-600’s tail fin separation in November 2001.

The long-awaited National Trans­por­tation Safety Board (NTSB) report of the controversial AA587 accident was finally published in January this year, containing some landmark recommendations about rudder control sensitivity and pilot training for recovery from unusual attitudes.

The A300-600’s tail fin separated during climb-out from New York Kennedy airport, following repeated rudder reversal inputs by the pilot flying in reacting to wake turbulence from an aircraft ahead. The manipulation overstressed the fin considerably, says the report, by inducing sideslip loads that exceeded its design specifications.

The NTSB says the primary cause of the fin detachment was excessive rudder input by the first officer, but it also cites as factors the relative sensitivity of the A300-600’s rudder controls, and elements of American Airlines’ upset recovery training, which it says could predispose pilots to use the rudder inappropriately. Airbus is working with the Federal Aviation Administration to determine whether it will demand modifications to the rudder pedal input forces and the amount of movement required to deflect it at higher speeds.

Since AA587, however, there has not been another fatal accident involving a large third- or fourth-generation passenger jet. The indications are that the world needs to concentrate on turboprop operators, as well as the perennial problems of old Soviet-built aircraft and air transport in poorer economies.