The Extraordinary Landing of TACA International Flight 110

The prototype for the first commercial jet airliner, the de Havilland Comet, first flew in July of 1949 and it actually turned out to be a troubled design. We still had a lot to learn, it was briefly withdrawn from service after three highly publicized accidents occurred just in the year 1956. But some 40 years after the Comet first started flying you think we would have learned our lessons and would have understood things like basic jet engine design or how weather interacts with engines. But the terrifying tale of Taka International Flight 110, May 24th of 1988, reminds us that Mother Nature still had some things to teach us about the weather and how it impacts a jet engine, and it is a story that deserves to be remembered. Taka International Airlines Flight 110 was a regularly scheduled passenger flight between San Salvador, El Salvador to New Orleans, Louisiana with an enroute stop in Belize City, Belize. The airplane was a Boeing 737-300. The 300 model was a second generation derivative of the venerable Boeing 737, a tested and reliable aircraft that had been in service for nearly two decades. In fact, this particular Boeing 737 was nearly new, having first flown in January of the same year and only having had been in service with Taka Airlines for two weeks. As a testament to how tested the design was, this 737 was the 1,505th to be manufactured. The plane was piloted by a veteran crew. 29-year-old Captain Carlos Dardano had amassed over 13,000 flight hours, more than 4,000 of those on the Boeing 737. Veteran First Officer Dionisio Lopez had more than 12,000 hours of flight time. And in addition, a third pilot, Pilot Instructor Captain Arturo Soli, was in the cockpit to monitor the performance of the nearly new airplane. In short, this was a routine flight with a veteran air crew, flying a nearly new airplane but of a venerable and tested design. That's as safe as it gets, problems with this flight simply should not have happened. The airplane, with 38 passengers and a crew of seven on board, departed as scheduled from Belize City and the flight was uneventful until descent into New Orleans from 35,000 feet. During the descent from 35,000 feet the aircraft encountered severe weather, very severe weather. The plane had in fact encountered an area of intense rainfall followed by 30 seconds of heavy hail. The storm intensity, stated in terms of liquid water content, was estimated to be 25 to 30 grams per cubic meter, which equates to rainfall at a rate of approximately 30 inches per hour. That should not have happened. The aircraft, like most all modern jet transports, was equipped with weather radar that displays information regarding the intensity of weather in the vicinity of the airplane. Weather radar is intended to provide the pilots with a depiction of weather in front of the plane, and may influence flight path decisions if the weather in front of the airplane is sufficiently intense. This radar looks very much like the radar that you see in the evening news, with green areas showing lighter precipitation, with yellow and red areas showing more moderate or severe precipitation. The veteran crew, seeing light to moderate weather in their path, adjusted their flight approach to go between the more severe weather, choosing an air approach that brought them on a due east approach to New Orleans. The pilots had done everything right, and had used their radar to avoid exactly the weather they encountered. So why had they hit such severe weather? It might be that the thunderstorm developed quickly, a phenomenon called a rapidly growing thunderstorm. But it also might have been something called radar shadow. On the weather radar screen, areas where no precipitation is seen by the radar are displayed as black, or the same color as the display background. However, when displaying extreme precipitation levels, the radar may display the highest intensities, that is worse than red, as clear on the radar screen. That is commonly known as radar shadow, and is a result of attenuation of the radar signal. In other words, it is possible for the worst weather to appear on the radar screen as the best weather. As they encountered the rain and hail, at about 16,500 feet, the pilot radioed New Orleans Aircraft Control, declaring an emergency. Both engines had flamed out. That means that the approximately 140,000 pound jet aircraft had suddenly become an unpowered glider, and the pilots were flying by dead sticking. The term is dated, and it's not referring to the flight controls, but to the period of propeller driven aircraft, where a loss of power would turn the propeller into nothing more than a dead stick. Trying to dead stick landing with a passenger airliner can be described as not ideal. Moreover, it should not have happened. The engine stalled due to something called a flameout, and that has to do with the basic idea of a jet engine. Every internal combustion engine has a combustion chamber, the place where the fuel air mix is burned. A jet engine basically includes a rotating air compressor powered by a turbine, with the leftover power providing thrust via a propelling nozzle. The process is known as the Brayton thermodynamic cycle. In short, the burning gases in the combustion chamber rush to the open back of the engine at high speed, providing thrust. Lose ignition, and you lose thrust. The engine on TACA International Flight 110 had ingested so much water that the flame in the combustion chamber had been doused. But that still should not have happened. The risk of water causing a flameout was understood at the time, and so the US Federal Aviation Authority had established a water ingestion certification procedure for all jet engine designs. Manufacturers reportedly tested their engines by shooting them with a fire hose. The rain that TACA Flight 110 encountered was supposedly well within these certification standards. Moreover, knowing the threat of weather, the pilots had taken appropriate precautions, switching the engine to continuous ignition and activating the engine anti-icing system. And yet both engines still had flameouts. Why? It all has to do with hail. According to the National Transportation Safety Board, prior to TACA Flight 110, the risk of hail was seen to be from the hail causing damage to engine components, essentially acting like a foreign object hitting the engine. Hail was not considered for its effect on engine operation. Jet engine fan designs were built with the idea of preventing water ingestion because the turbine fan blades centrifuge water away from the engine core. It was assumed that hail would work pretty much the same as water, but testing after the accident determined that it doesn't. In fact, hail follows a much more ballistic path that, at the right air speed and turbine speeds, allows the hail to shoot straight into the engine core. In fact, the FAA realized at some fan speeds and aircraft airspeed combinations, ingestion in the core is greatly increased as hail misses the fan blades and goes directly into the core, something commonly called the Venetian blind effect. Standards designed to prevent water from entering the engine failed because of the combination of airspeed, turbine speed, and hail. But even a double engine flameout should not be catastrophic because an engine that is flamed out can be restarted just by the wind blowing through the engine turning the turbine, something called a windmill restart. And even if you don't have enough airspeed to do a windmill restart, you can fire up the engine's starter motors and restart the engine that way. Just the previous year, an Air Europe 737 descending through rain and hail over Greece had also suffered a double flameout, but the crew managed to restart the engines and land without trouble. Likewise, the crew of TACA Flight 110 attempted to restart the engines. When the windmill restart failed, they were able to get the turbine spinning using the starter motor, but the engines could not get to idle speed and were not producing thrust. There was still too much water in the engines. As the FAA explains, once the engine fails, it cannot be restarted until the water-to-air ratio decreases to a point where the fuel-to-air ratio can once again maintain combustion. Now the situation was desperate, the plane was without power and low altitude and turbulence from the storm gave them a limited glide ratio. Air traffic control quickly came up with options, including Lakefront Airport whose runway was minimally sufficient, and US Interstate 10 which has one straight mile for every five miles of highway. Unable to make it to either of these, the pilots opted for a vector to Lake Pontchartrain, attempting a dangerous dead stick water ditching. New Orleans Air Traffic Control lost the transponder signal as the aircraft reached 1600 feet. They assumed the aircraft had crashed and quickly dispatched a Coast Guard helicopter from Naval Air Station Joint Reserve Base New Orleans, assuming that the water rescue would be critical. What those helicopters found, frankly, should not have happened. TACA Flight 110 was parked on a narrow, muddy New Orleans levee, right next to NASA's Michoud Assembly Facility. At just 700 feet, First Officer Lopez had seen the levee and identified it as being wide enough for a landing. The crew had managed a maneuver called a side slip, something generally reserved for a small craft, not an unpowered 737, and had landed perfectly, with no injuries to passengers or crew and minimal damage to the aircraft. As one New Orleans air traffic controller said, after more than two decades of air traffic control, I still say, this is the most splendid piece of air traffic teamwork and the most incredible piece of flying I've ever been witness to or heard of. The flight crew had mere seconds to assess the situation as to whether it's the lake or the field, and they nailed it. After the accident, the National Transportation Safety Board mandated a change to the water ingestion standards and certain changes to the CFM-56 engine that's used on the Boeing 737. Those included changing the engine spinner from conical to a combination elliptical and conical, or coniptical shape, that testing shows helps to guide the hail radially outward. A change in the spacing of the fan blades to better deflect hail away from the engine core, a sensor to force the combustor to continuously ignite under heavy rain, and extra bleed doors to help drain water from the engine. The plane was minimally damaged, repairs to the engine were made on site, and the plane was towed to NASA's Michoud facility nearby, where after further repairs, it used the facility's main road, Saturn Boulevard, to take off and fly to a full repair facility. Saturn Road had at one time been a factory airfield, as airplanes were manufactured on the site during the Second World War. After repairs, that 737 was put back into service with Taka Airlines, eventually it was sold to Southwest Airlines and it continued service until it was retired in December of 2016. But despite 28 years of service, it was really that one extraordinary landing, a landing that frankly should not have happened, that most deserves to be remembered. I'm the History Guy and I hope you enjoyed this edition of my series of short snippets of forgotten history about 10 minutes long. And if you did enjoy it, please go ahead and click that thumbs up button, which is there on your left. If you have any questions or comments, feel free to write those in the comment section, I will be happy to personally respond. And if you'd like more snippets of forgotten history, all you need to do is subscribe.