In Icing, Extra Speed Provides a Margin of Safety

While on approach to land at Lubbock International Airport in Texas, in darkness about 5 a.m. on January 27, in conditions of freezing drizzle and mist, the Empire Airlines-operated ATR-42 twin-turboprop cargo hauler crashed about 300 feet short of the runway threshold.

The aircraft was destroyed but the two pilots survived.

The National Transportation Safety Board (NTSB) has launched an investigation. The NTSB investigators will doubtless find much on which to comment.

First of all, airplanes are not certified to fly in freezing drizzle conditions, where water droplets smack onto the wing leading edges and freeze. This condition – known technically as supercooled large droplet (SLD) icing conditions – constitutes about 1% of all icing encounters, but airplanes are not tested to handle it, nor are they certified for flight in this not-that-rare condition. Icing, yes, airplanes are tested and certified to handle this condition, but water droplets just above the freezing temperature that can hit a super-cold wing and freeze? Nope. Despite a longstanding NTSB recommendation that SLD be accounted for in approving an airplane design, the Federal Aviation Administration (FAA) has relegated this problem to the “too hard” pile.

Now here’s another airplane that’s crashed, most likely in SLD icing conditions, while the FAA dithers.

Second, the crew may not have been aware of the danger they were in. The good news is that the crew survived to tell the tale and to flesh out details of aircraft performance captured by the flight recorders. What the recorders and crew may well substantiate is that the pilots were right on the normal approach speed. With the ATR-42’s poor record in icing (and that of the stretched ATR-72, too), this crash about 300 feet short of the runway threshold is likely to be related to the airplane’s higher stalling speed due to carrying a massive load of ice brought about by the freezing rain/drizzle conditions.

Normal threshold speed is 1.3 times the stall speed in the landing configuration. But when the wing is contaminated, the stall speed goes up. When the iced-wing stall speed reaches 1.3 times the old clean wing speed, the loss of lift can be dramatic and sudden. The airplane will roll, pitch and lose altitude. A crew caught unawares must be quick on the controls to avert catastrophe. To be sure, they must have sufficient altitude in which to recover the airplane. An airplane just 300 feet shy of the runway threshold is mighty low for any recovery attempt, even if the crew reacts instantly and correctly.

My betting is that the pilots were right on the normal approach speed YET UNAWARE that their wing’s new stall speed (with the growing ice load on wing, fuselage, tail and control surfaces) was about 1.3 times the old clean wing stall speed.

Third, the NTSB will explore Empire Airlines training and operational procedures for flight in icing conditions and, if past accident investigations are any indication, organizational lapses outside of the cockpit, at the company level, will be found.

Fourth, the NTSB may well find that the industry does not profit from foreign accident investigations of icing-related incidents, in which systemic shortcomings are exceedingly well documented.

A case in point relates to the report issued in January 2009 by the Accident Investigation Board Norway (AIBN) regarding an icing-related incident involving a Coast Air ATR-42 in September 2005. The airplane had three crew and 24 passengers aboard and experienced the classic symptoms of icing induced stall. From the AIBN report:

“While climbing, when passing FL100 (approx. 10,000 feet), ice began to form on the aircraft. The aircraft’s de-icing systems were switched on and functioned normally. Nevertheless, more ice built up and, when passing through FL120, there was a marked reduction in the aircraft’s climb ability. At FL140, the autopilot disconnected, at much the same time as the aircraft entered an uncommanded roll to approx. 45 degrees to the right and began to lose height. When the crew believed they had regained control, the aircraft suddenly rolled uncommanded to the left in a similar manner. Around one and a half minutes after the first uncommanded roll movement, the climb was stable once more. The flight continued to Gardermoen [Oslo] without any further problems.”

The investigation documented the following:

“• Serious deficiencies in the company’s quality system and flight safety program.

“• Insufficient follow-up and rule enforcement on the part of CAA-N [Civil Aviation Authority – Norway, the country’s equivalent of the FAA] after it had disclosed serious deficiencies in the quality system and flight safety program in its flight operations inspections of the company over several years prior to the incident …

“In the opinion of the AIBN, this case illustrates the importance well functioning safety regulation has on aviation safety. The failure of the CAA-N follow-up contributed to deficiencies in the Coast Air quality system and flight safety program not being corrected in time.”

Later in the report, the AIBN documented damning particulars of the case:

“The fact that, at the time of the incident, Coast Air had not drawn up a policy on the use of weather radar indicates a low level of awareness about the hazards to which the company’s operations were exposed …

“The crew’s explanation indicates that they did not perceive that they were entering severe icing after they registered ice accretion after passing through FL100. The time from when the ice accretion had a significant effect on the ability to climb until control was lost was about 3 minutes … This indicates a lack of knowledge about the hazards connected with icing. In accordance with the procedure, the minimum speed in severe icing should be 10 kt greater than in ‘standard icing,’ that is a minimum of 153 KIAS. The crew therefore did not have the safety margin they assumed since they allowed the speed to drop to 150-155 KIAS. This indicates a lack of knowledge about current procedures.

“[The] hazard of icing was not given particular emphasis in the company’s program for training and flight safety. If the flight crews are weak in any knowledge about a subject, it is particularly unfortunate if the company’s flight operations documentation is inadequate …

“The AIBN has the impression that the quality of the periodic training under Coast Air’s management was reduced in order to keep costs down.”

I am willing to bet that very similar findings may result from the NTSB’s investigation of the Empire Airlines ATR-42 crash at Lubbock – lack of pilot knowledge, lack of company awareness and training, economic pressure, absence of FAA certification standards and lack of FAA oversight of the airline.

Icing is often hard to track on radar, but the factors cited in the Norwegian report are eminently quantifiable and amenable to corrective action. As we continue to fly these winter months, the Norwegian report is a case study in regulatory neglect that is likely to be repeated by the NTSB inquiry into the crash at Lubbock.

In the meantime, there’s a phrase in aviation, to the effect that “speed is life.” In icing conditions, extra speed is a vital protection against catastrophe. In both the Coast Air and Empire Airlines cases, extra speed was a safety margin that probably wasn’t present, and wasn’t emphasized by the company.

The complete AIBN report may be viewed at: