Aircraft Accidents and Lessons Unlearned XXI: US Air Flight 405

On March 22, 1992, at 21:35 Eastern Standard Time, US Airways Flight 405, a Fokker 28-4000 airliner, crashed at LaGuardia Airport during its takeoff roll. As per National Transportation Safety Board (NTSB) accident report AAR-93/02, the aircraft rotated off Runway 13, but immediately lost lift, rolled left, hitting an Instrument Landing System (ILS) Localizer Antenna and a Pump House. The aircraft came to rest partially inverted in Flushing Bay.

NTSB accident report AAR-93/02 determined the Probable Cause of the accident to be, “the failure of the aviation industry and the Federal Aviation Administration (FAA) to provide flight crews with procedures, requirements and criteria compatible with departure delays in conditions conducive to airframe icing and the decision by the flight crew to take off without positive assurance that the airplane’s wings were free of ice accumulation after 35 minutes of exposure to precipitation following deicing. The ice contamination on the wings resulted in an aerodynamic stall and loss of control after liftoff. Contributing to the cause of the accident were the inappropriate procedures used by, and inadequate coordination between, the flight crew that led to a takeoff rotation at a lower than prescribed air speed.” US Airways or their procedures were not even mentioned in the Probable Cause or Recommendations.

The NTSB displays confusion in this accident. Even when accident report AAR-93/02 cites a germane problem on page 76, Finding 20: “Accident history shows that non-slatted, turbojet, transport-category airplanes have been involved in a disproportionate number of takeoff accidents where undetected upper wing ice contamination has been cited as the probable cause or sole contributing factor,” the NTSB shrugs off the glaring fact. The NTSB alludes to this critical issue in Recommendations A-93-24 and A-93-25, suggesting testing be conducted between the FAA and the National Aeronautics and Space Administration to “explain the disproportionate number of takeoff accidents of non-slatted airplanes.” That’s it? By their own admission, in 1992, an inconsistent number (???) of non-slatted aircraft are having accidents on takeoff in icing conditions – enough for the NTSB to take notice of – but the NTSB’s focus was on making sure ILS antennas are made of breakable material?

A non-slatted winged aircraft does not employ leading edge slats, like those used on many commercial aircraft. One term for these wings is: ‘critical wing’; the camber is flatter on both upper and lower wing surfaces, which makes the lift produced dependent on a smoother surface – no contamination. Any ice – even granular ice – can disrupt airflow over the wings enough to be a threat.

In 1992, Title 14 Code of Federal Regulations (CFR) Part 121 airliners with critical wings were not as numerous as they are today. In this report, the NTSB ignored the safety ramifications of many CFR Part 135 aircraft employing non-slatted wings. This opportunity to address the safety of a large population of aircraft was lost, even though the NTSB recognized that non-slatted aircraft accidents were occurring. Instead the NTSB wrote about a confused jumble of ‘contributors’ to Flight 405’s accident using ambiguously soft language, e.g. “encourage air traffic control …” or “establish a wind tunnel …”; words that have the urgency of saying, “pretty please with sugar on it.” As per AAR-93/02, “At the time of this accident, US Air was using Type I glycol-based fluid for deicing airplanes. As with other domestic air carriers, US Air had not equipped any of its facilities to dispense the Type II fluids to provide extended anti-ice protection to its aircraft.” The choice of only using Type I deicing fluid generated specific aircraft holdover time (HOT) numbers: the time between the moment deicing starts on an aircraft and when that aircraft must begin its takeoff roll.

US Airways was within their rights to only use Type I deicing fluid. It is, however, important to clarify the difference between Type I deice fluid and Type II anti-ice fluid. Some aviation ‘experts’ suggest it is acceptable for a flight crew to ignore an air carrier’s approved deicing policies and use, e.g. a push broom, to remove ice and snow from an airliner, even one with a critical wing. It is/was not acceptable; it is/was dangerous; it is/was wrong … period, for deicing an airliner.

Deicing fluid (DF) is usually – not always – glycol- or ethanol-based. DF is mixed within the delivery system, e.g. a deice truck, with water and heated to near the boiling point of water. The mixture percentages are important and must be known to determine the HOT. The heated DF is sprayed on the fuselage, wings and empennage to melt/clear ice and snow. If the deicing event starts at the cockpit, then the HOT is calculated from the moment the DF is applied at the cockpit – not later. The heated fluid contacting the cold airframe, cools down dramatically and runs off leaving very little residual protection from snow or refreezing. This is why HOT times are so critical. As per AAR-93/02, the HOT for the Type I DF used on Flight 405 was eleven minutes and thirty-seven seconds.

Anti-ice fluid (AIF) is not heated or diluted. Instead the ambient temperature AIF is applied as a coating of pure glycol or ethanol immediately after the aircraft is deiced; the AIF retards the ability for snow or ice to rebuild. AIF has a longer HOT because of its superior negative effect on frozen precipitation, but it does not last forever. Constant precipitation affects AIF’s integrity, but its protection has a greater HOT than DF. AIF was not used on Flight 405; its absence better explains what went wrong.

Flight 405 was originally scheduled to depart Gate One at 19:20. The first deicing was at 20:26, an hour later. The Captain called for a second deicing because a broken deice truck blocked Flight 405’s path. The second deicing ended – concluded at – 21:00 (per US Airways deicing records). Properly deicing an entire airliner the size of a Fokker 28-4000 with one deice truck takes a minimum of ten minutes; a larger B727 with a similar T-tail takes ten minutes to deice, per my experience. Flight 405’s deicing started at 20:50 – forty-five minutes before the takeoff roll; thirty-three minutes after Flight 405’s HOT expired.

If this was the first time icing caused a major airline accident, the NTSB’s ignorance could be excused. However, Air Florida Flight 90 (January 1982) and Arrow Air Flight MF1285R (December 1985) occurred within the previous decade; they were hard, costly lessons where icing was ignored to the tragedy of many lives lost. These two accidents were cultural issues, as was US Airways Flight 405.

So, what did go wrong that tragic night? Both the NTSB and the FAA have made the term ‘Pilot Error’ an ambiguous phrase, applying to anything that can’t be figured out via hard work and attention to detail. It’s a rubber stamp for those who don’t understand what really happened in an accident. However, according to AAR-93/02’s Recommendations, Air Traffic Control’s attention to detail did not cause this accident. The FAA could not look-over-the-shoulder of the pilots that night. The airport firefighters’ response time had less to do with Flight 405 ending up in Flushing Bay as did the ILS antenna’s lack of frangibility.

This time ‘pilot error’ referred to the pilot’s actions before the flight. This accident’s root cause was the flight crew’s failure to follow frozen precipitation event procedures. Critical wing or no critical wing, one of the pilots should have assured the wings were airworthy by conducting a ramp visual inspection – outside – at the wings or calling again for deicing. The Reason: Flight 405’s second DF HOT was exceeded by thirty-three minutes. Ice and snow had re-accumulated on the wings.

Flight 405’s tragedy was not because of gate holds, airport taxi delays, other airlines using incorrect procedures, ground personnel’s professionalism, briefing cards or ILS antennas’ frangibility, as AAR-93/02’s Recommendations would suggest. Two pilots defied their training and common sense; they, alone, ignored the DF HOT. Whether lulled into a false sense of security, thinking that the Laws of Physics would forgive them this oversight or just their refusal to stand outside in the snow, the pilots failed to protect the flight. Twenty-six other people paid the ultimate price for this error in judgment.

The NTSB continued to fail in their understanding of airline culture, thus neglecting their responsibility to the travelling public. What is the purpose of an accident report? To find out what caused the accident … the accident … the accident. Instead, AAR-93/02’s Probable Cause watered down the HOT issue by blaming the FAA, air traffic control, the entire airline industry and the aircraft manufacturer. The NTSB leap-frogged over the non-slatted critical wing icing issue that affected Part 121 and Part 135 aircraft, even though they questioned it. Twenty-seven years later, the NTSB still does not understand airline culture. Twenty-seven years later, we still have Lessons Unlearned.