Dear Captain Lim,
How does heavy rain affect the Boeing 777 engines? Do they fail because of the rain?
What does adverse weather do to a plane like Boeing 777?
You mentioned that when engines fail, a plane could be glided to land safely. I imagine most crashes are due to engine failure e.g. the most recent Kenya Airways in Cameroon.
Why couldn*t the pilot glide into those mangrove forests to at least minimize the impact but it looked like the plane was directly catapulted into the swamp with maximum force.
The Boeing 777s have very reliable engines. They have to be because they are certified for ETOPS. Furthermore, their inspection and maintenance schedules are more stringent than those of the Boeing 747-400s.
During the development of the jet engines, they are subjected to water and "chicken gun" test. Amongst others, the manufacturer is required to demonstrate the plane's ability to satisfy this "chicken gun" test - where fake gelatin birds are fired at the engines through a large cannon. Engine that sustained damage have to be redesigned.
So the engines of the Boeing 777 can take far more punishment than what most people are led to believe. Yes, modern jets can usually fly safely through stormy clouds when it becomes unavoidable.
What about the Boeing 737? It is hard to say as it belongs to a different class. Unlike the Boeing 777 which is certified to fly on one engine for more than three hours for ETOPS certification, the Boeing 737 (older ones before the Next-Generation variants) are mainly used on short haul flights. Well, however rare the occurrences of engine failures are, there have been incidents where engines have flamed out during flight through severe thunderstorm and rain.
In August 1987, a Boeing 737 of Air Europe was descending through rain and hail to land in Greece when both of the plane*s engines experienced a flameout. The pilots were able to relight the engines and land safely.
In May 1988, a TACA Boeing 737 flight from Belize to New Orleans, Louisiana, was passing through a series of thunderstorms when it too suffered a double flameout. The crewmembers managed to briefly restart the engines but were forced to shut them down again because of overheating. The pilot managed to glide the plane on a grass strip next to a levee embankment along a lake.
Then in 2002, a Boeing 737 belonging to Garuda Indonesia also experienced a similar engine failure. Like the earlier cases, this flight was also flying in heavy storms when both engines flamed out. Unable to relight the engines or reach a landing site, the crew ditched successfully on a nearby river with only one casualty - a flight attendant.
As regards to the Kenya Airways Boeing 737-800 crash at Cameroon on 5th May 2007, the plane was only about 6 months old and it was a "Next Generation" model - unlike the three older B737s that had engine failures above. Thus, it is still unclear whether the plane was brought down by heavy rain. Although modern jets can usually fly through stormy clouds, storms in Africa are particularly violent at this time of the year, one of the investigators said.
But the head of weather observation at the airport said that the rain was unlikely to have caused the crash as there were other planes that left (after the Kenya Airways flight) had encountered no problems.
Preliminary investigations revealed that the plane went into a 90-degrees nosedive; this may be due to a violent gust of wind within a thundercloud flipping the airliner over. It crashed just 3.4 miles from the runway. Using speed calculations, experts estimate the plane had been in the air for just 30 seconds and had never climbed over 3,000 feet. The low altitude would have made it impossible to recover from the resulting dive.
Couldn't the plane be glided to land safely?
The Associated Press quoted an official close to the investigation as saying the jet may have flown through an intense storm that caused both engines to fail and that the pilots were trying to glide the stricken jet back to the airport.
If that were true, and according to the estimates above, the plane had never climbed over 3,000 feet, there was no way that the plane could have glided the stricken jet successfully back to airport.
For a straight-in total loss of power approach, the aircraft must be positioned on the extended centerline of the runway at a minimum height equals to 4 times the distance out - e.g. at 15 nautical miles, the pilot must aim to be at 6000 feet. In the instant case, it appears that the plane did not have that kind of altitude or distance to achieve a successful glide. Further, the severity of the impact indicated that the plane was nowhere settled down on a glide even if it could.
Investigators said they couldn't yet discount other factors, including mechanical failure, pilot disorientation or even sabotage. But the search teams have found no sign of a blast or fire so far. (As mentioned in an earlier FAQ - I would not like to speculate the exact cause of the crash until the official finding is over)