Two safety recommendations regarding windshield heating systems have been issued by the National Transportation Safety Board (NTSB), however, the Federal Aviation Administration (FAA) has yet to take action, and windshields continue to crack.

The latest incident occurred 30 January 2008, when an American Airlines B757 en route to Philadelphia from San Juan, Puerto Rico, was forced to divert to West Palm Beach, Florida, making an emergency landing after the cockpit filled with smoke.

According to the NTSB, several of the 146 passengers and crew were hospitalized for smoke inhalation. All have since been released.

According to reports from the crew, while at cruise altitude over the Atlantic Ocean, smoke began coming from the heating system connected to the first officer’s windshield (see photo 1). The crew donned oxygen masks and smoke goggles and diverted to Palm Beach International Airport. During the descent to land, the inner pane of the first officer’s windshield shattered, further compromising visibility (see photo2).

The crew continued the descent and landed without additional incident.

The incident is now under investigation. The digital flight data recorder (DFDR) was downloaded and sent to the NTSB laboratory in Washington D.C. The affected windshield, which remained in one piece, and the heating unit, were removed from the aircraft for detailed analysis by NTSB investigators.

While the cause of this incident is under investigation, the NTSB indicates that there have been at least five events between 2004 and 2006 in which smoke and, in some cases fire, were reported to have originated in windshield heating systems on B757 aircraft. Based on these incidents, in September 2007 the NTSB issued safety recommendations to the FAA asking that redesigned heating systems be required for installation on all B747, B757, B767 and B777 aircraft (see box).

These recommendations have yet to be implemented.

In terms of the investigation into this recent incident, a number of issues are germane, including:

Who was the pilot flying when the incident first occurred? If it was the first officer, in the right seat, did he relinquish flight controls to the captain because of the obscured vision caused by the extensive cracking of his windscreen?

The NTSB indicates that the crew donned oxygen masks and smoke goggles. Does this phraseology indicate they did not have one-piece units that are easier and quicker to place on the head.

• Who among the flight crew had to be hospitalized for smoke inhalation? If not the members of the cockpit crew, then flight attendants were affected. If so, did the flight attendants don emergency breathing equipment? If they did, why were some still treated for smoke inhalation. If masks were not used by the flight attendants, why not?
• How much smoke was produced by the failed heater unit? With seven people evacuated to the hospital, clearly smoke wafted into the cabin. That likely indicates the smoke was pretty thick in the cockpit. Was the smoke thick enough to obscure instruments and/or the view out the windscreen?
• Would a cockpit video recorder have been useful for assessing the amount of smoke in the cockpit? The NTSB has called for video recorders in the cockpit, and this incident seems to represent a good illustration of where such video recordings would be of merit.
• How much time elapsed from the onset of smoke to the landing?
• Was the 30-minute recording time for the DFDR sufficient to capture the full incident? If not, how much data from the incident was lost?
• Was the cockpit voice recorder (CVR) downloaded as well, and was its 30-minute capacity sufficient? Recall that the NTSB has recommended a two-hour recording time for both the DFDR and the CVR.
• What smoke evacuation procedures were applied by the crew and were they successful?
• Was the aircraft fitted with the improved heater unit design? If not, why not? If it was, how did the improved unit fail?
• Did the crew pull the circuit breaker for the failed heating unit when it began to emit smoke.
• Obviously, these and other questions bear asking, as the failed heater unit exemplifies a “single point of failure” that is either supposed to be an extremely remote possibility, or otherwise redundancy is required.

Photo 1:

Failed heating unit on the affected windshield. Source: http://ntsb.gov/Pressrel/2008/images/AA-757-heater_block.jpg

Photo 2:

Cracked windshield on the B757 from inside the flight deck.Source: http://ntsb.gov/Pressrel/2008/images/AA-757-cockpit.jpg