@Astro14 @lurker
Let's say you were cruising at 39,000' and the OAT is -90°F. The combustion is maintained by the engine compressing air, heating it, and fuel being injected. I don't know the minimum required temperature to maintain combustion, but I would guess around 500°F. What happens to combustion if you have to do an emergency descent and you pull the engines to flight idle? Can the compressor stage maintain enough heat to support combustion? Do you have to do anything before pulling the engines to flight idle when it's seriously cold outside?
The part about the emergency descent is irrelevant because we always descend at idle ( unless a small altitude change ).
The only difference in an emergency descent is speed and speed brakes ( high rate of descent...7000 Feet per minute ) and we only do this if we lose cabin pressure entirely ( or some other major reasons have to get down fast like cargo fire, smoke in cockpit, etc ).
No, it won't cause any problems for combustion and there are no issues with just "pulling em back" to idle ( well, we put the engine anti-ice on at times ) whether in a normal descent or emergency descent.
The only outside air temp limit is -94 F ( flight envelope certification limit ) above 32,000 and planning to avoid flight at altitudes where the temperature is -85F or less ( for fuel reasons ). Talking about the Airbus here.
The only thing that will cause combustion problems is torrential rain that exceeds engine certification limits ( B737 in Africa that flamed out after flying into severe weather and another near Louisiana ). I am talking about extreme weather and flying right into it.
34 Years Ago This Week - The Miracle Of TACA Flight 110
BY LUKE PETERS
PUBLISHED MAY 22, 2022
How a flight crew skillfully averted disaster following a double engine failure.
Photo:
Airliners.net via Wikimedia Commons
Many readers will be familiar with the story of US Airways Flight 1549, the so-called 'Miracle on the Hudson' with Chesley 'Sully' Sullenberger at the controls. Yet in 1988, a remarkably similar incident befell the crew of a TACA International Boeing 737-300. This is the story of how the crew on that flight also pulled off a remarkable landing, saving not only the aircraft but all passengers and crew onboard The story became known as the 'Miracle on the Levee'.
History of TACA flight 110
On May 24th, 1988, flight 110 was on a routine scheduled flight from Belize City to New Orleans, USA. The flight that day was operated by a Boeing 737-300 registered N75356. TACA flight 110 was a regularly scheduled passenger flight between San Salvador, El Salvador, and New Orleans, Louisiana, with an en-route stop in Belize City, Belize.
This aircraft was almost brand new, having only had its first flight on January 26th, 1988. It had only been in service with TACA for just two weeks since joining the airline from US-based Polaris Leasing before operating flight 110. The aircraft (MSN 23838) was Boeing's 1,505th 737 off the production line.
N75356 had been flying for TACA for just two weeks. Photo:
Howard J Nash via Wikimedia Commons
That day, the operating crew on flight 110 comprised Captain Carlos Dardano (aged 29), who had 13,410 total flight hours of experience, with almost 11,000 of these as pilot-in-command. The first officer, Dionisio Lopez, was also very experienced, with more than 12,000 flight hours logged.
Captain Arturo Soley, an instructor pilot, was also in the cockpit, monitoring the performance of the Boeing 737-300, which was a new type of the airline's fleet, although it had operated the 737-200 for years.
With 38 passengers and a crew of seven onboard, the flight departed Belize City's Philip S.W. Goldson International Airport. It was planned to fly across the Gulf of Mexico, crossing the Louisiana coast, before making its descent and approach to New Orleans International Airport.
Double engine flame-out
As flight 110 proceeded along its flight path, it commenced its descent towards New Orleans. Passing through 35,000 feet (10,500m), the flight crew noticed extensive thunderstorm activity displayed on their weather radar on the flight deck of their brand new aircraft.
Alongside some isolated areas of heavy precipitation being displayed on their path ahead, the pilots did what they could to avoid the worst of the storm, flying between the heaviest areas of rain, shown as red 'weather cells' on their onboard display.
At 30,000 feet (10,000m), the flight entered thick cloud, and the pilots selected the 'continuous ignition' switches for both engines to 'on'. They also turned on the anti-ice systems to protect the engines from the heavy rainfall and potential icing conditions, which can cause a 'flame-out' where both engines lose power.
Despite the crew's best efforts, however, the aircraft entered an area of the storm and encountered severe rainfall, combined with hail and turbulence. As the plane descended through 16,500 feet (4,950m), both CFM-56 turbofan engines experienced total flame-outs, causing the loss of all thrust and electrical power onboard.
This left the stricken aircraft gliding downwards with neither engine producing either thrust or electrical power. The crew had already selected the thrust levers to flight-idle power setting in preparation for landing just before the flameout occurred.
Attempts to re-start the engines fail
The crew, following standard operating procedures, started the aircraft's auxiliary power unit as the plane descended through 10,500 feet (3,150m), which managed to restore electrical power and hydraulics to the aircraft, giving the pilots some maneuvering capability but also crucially, the power required to attempt to re-start the engines - using the 'windmill' effect of air passing through the fan at the front of the engines to re-start them.
However, although the crew managed to restart the engines, neither produced more than idle power. This resulted in the aircraft having no meaningful thrust and preventing the crew from maneuvering the plane towards New Orleans International Airport.
Attempts to advance the throttles only resulted in overheating the engines, so the pilots eventually decided to shut down both engines to avoid engine damage, or worse still, an engine fire.
Unable to reach a suitable airfield
As the crew realized the grave situation they found themselves in, the first officer transmitted a 'mayday' call over the radio to New Orleans air traffic controllers. Despite their best efforts to vector flight 110 towards the airport, the aircraft could not make the distance remaining, given its lack of propulsion at this point.
The controllers offered a potential landing site at nearby New Orleans Lakeland Airport as an alternative. However, with height and airspeed both receding rapidly, the pilots knew that they could not reach this alternative landing site either.
Having abandoned attempts to re-ignite the damaged engines, the three pilots scanned the immediate area off the nose of the aircraft for possible sites for a forced landing. Given the altitude and airspeed remaining, no other hard runway landing sites were available.
Consequently, the crew was facing the unenviable task of executing a water-based landing upon the swampy wetlands of Louisiana.
As flight 110 descended through the lower layer of storm clouds and the clear sight of the ground became possible, the pilots noticed a wide drainage canal straight in front of the aircraft. With the flaps and gear retracted, the crew reluctantly decided to ditch their new plane in the canal.
Captain Dardano lined up with the canal located near an industrial area east of the city. He stretched the glide to try to have it glide the longest possible distance without stalling while the first officer ran through the ditching checklist, configuring the aircraft for a water landing.
Suddenly, the first officer noticed a long grass levee to the right of the canal. A levee is a raised embankment built to prevent the overflow of a river or waterway. This levee was on the grounds of the NASA Michoud Assembly Facility in eastern New Orleans, near the Intracoastal Waterway and Mississippi River Gulf Outlet.
He suggested to the captain that an emergency landing be attempted on that. Captain Dardano agreed, and he subsequently carried out a successful landing of the aircraft along the top of the grassy levee to the side of the canal, bringing the plane to a halt with distance to spare.
The incredible landing was executed atop a grass strip section of the levee measuring 6,060 feet by 120 feet wide (1,818m by 36m). Miraculously, the aircraft sustained minimal damage in the forced landing attempt, and there were no serious injuries amongst any of the 38 passengers or seven crew members.
The investigation of Flight 110
Following an extensive investigation led by the National Transport Investigation Bureau (NTSB), it was found that flight 110 had inadvertently flown into a level 4 thunderstorm. Water ingestion had caused both engines to flame out during descent with a lower engine power setting. This was despite the CFM-56 powerplants being certified to meet the Federal Aviation Administration (FAA) standards for water ingestion.
The engines were severely damaged by hail ingestion and ice damage, and the number 2 engine (starboard side) suffered additional damage from overheating. The aircraft sustained mild hail damage to its nose and cockpit area, but miraculously, the airframe remained relatively unscathed from its close scrape with Mother Nature.
