747-8F suffers ice damage to three engines

In what proves that engine icing is still a less than understood phenomenon, an AirBridge 747-8F (VQ-BGZ) flying between Moscow and Hong Kong suffered damage to three engines, and a power loss in two during an icing event.

The report says that the aircraft was cruising at 41,000 feet near Chengdu, about 1.5 hours before landing, when there was a temperature rise shown on systems in the cockpit. The temperature went from -54C to -34C. The crew had changed course to avoid a thunderstorm, and flew through a cloud that didn't show up on weather radar.

They put the engine ice protection into manual, instead of automatic and flew that way for almost ten minutes before going back to automatic. Around 20 minutes later, the number two engine (inboard left), suffered a surge and an automatic restart. Two minutes later, the outboard left engine (#1) went to 70% power, while #2 remained at idle.

After landing, and inspecting the engines, it was found that three of the four engines (#1, #2, and #4) showed first stage high pressure compressor blade damage from ice. The aircraft suffered a crystal icing event, which is not well understood, and extremely difficult to detect, on the unheated portions of the high-pressure compressor.

Icing has always been a problem for aircraft that fly high enough. American Eagle 4184 crashed, killing everyone on board after flying into icing conditions where the rain hit the wing, and rolled back behind the deicing boots before freezing. British Airways 38 was also caused by ice building in the fuel system. I've also seen four B-1s grounded for maintenance after ice went through their engines. It's a constant battle to figure out new ways to detect and prevent ice.

Russian authorities are investigating an serious icing incident in cruise during which three engines on a Boeing 747-8 freighter sustained damage and two suffered a loss of thrust.

Federal air transport authority Rosaviatsia identifies the aircraft involved as an AirBridge Cargo 747-8F, registered VQ-BGZ. The 747-8F is powered by four General Electric GEnx-2B engines.

It had been operating between Moscow Sheremetyevo and Hong Kong on 31 July, and was cruising at 41,000ft at the time.

The incident occurred at night in the vicinity of Chengdu, about 1.5h before landing, as the aircraft deviated to the right of its intended flightpath in order to avoid a thunderstorm.

www.flightglobal.com...

It is interesting to hear that there is still enough humidity in the air 12.5 km up to help contribute to this effect. I know it gets cold up there so that factor is well covered.

This is why Iron Man went with the gold titanium alloy.
Doesn't anyone watch movies anymore?
Sheesh!

reply to post by Zaphod58


Very interesting thread. Still an unsolved phenomenon - the extreme density of the ice crystals at altitude over the tropics. I read two accounts - one showing that this has been a problem (on the order of once a month) since 1988 and one that said since the early 1990's. The cloud, invisible to radar, seems to be visible to the crew. Is that right or is it just assumed because of effects that they went through one?

This is a very interesting and little understood problem, and a lot more detail has come out now, including potential fixes.

The crew noticed an anvil cloud ahead of them, and diverted around it. As they diverted (as was stated in the original story), the temperature rose 20C to -34C for a minute and a half or so. It was thought that at that altitude the ice would pass through bleed ducts, melt inside the engine, or just bounce off structures, as it's believed to be too high for clouds to have supercooled liquid water in them.

Instead investigators are finding that there exists a specific range of conditions, always apparently near convective clouds, where under a specific mix of airflow, water, and ice, that ice can occur and build up near the core of the engine, causing a power roll-back, or thrust loss with no warning.

Within a couple weeks of this incident, Boeing and GE introduced software changes to the GEnx-2B engines used on the 747-8 FADEC that will allow the engine to detect ice crystals forming in the engine. If detected the engine will open variable bleed valves to eject the ice from within the engine.

Cruising in darkness at 41,000 ft., on July 31 near Chengdu, China, the crew of an AirBridge Cargo Boeing 747-8F were beginning to prepare for the descent into Hong Kong when they deviated to avoid a thunderstorm clearly depicted on the weather radar.

Even if they had been able to visually check their surroundings, they would not have noticed anything unusual about the area they penetrated in the outflow region of the anvil cloud trailing the relatively distant storm. There was no sign of airframe icing, nor any echoes from the radar.

Yet the cloud was full of undetectable ice crystals that—within minutes of the encounter—caused significant damage to three of the aircraft's four engines, one of which lost thrust while another surged. The AirBridge Cargo (ABC) crew had unwittingly come face-to-face with core engine icing, a poorly understood phenomenon that has been striking a wide variety of aircraft and engines on a growing scale since the 1990s. As well as surges and mechanical problems, the previously unrecognized form of icing inside engines causes thrust loss, or power “roll-backs,” with virtually no warning.

According to Russian federal air transport authority Rosaviatsia, chief investigators of the 747-8F event, the crew saw at least one typical clue to the phenomenon. Entering the area of ice crystals, the total air temperature (TAT) rose by 20C to -34C for 86 sec. The crew reacted by switching the engine ice-protection system from automatic to manual for about 10 min. But approximately 22 min. after flying through the warmer sector, the aircraft's No. 2 (inboard left) engine surged and automatically restarted. The No. 1 engine then experienced a speed reduction of 70% of N1 (low-pressure rotor speed). After landing at Hong Kong, inspections revealed damage to the high-pressure compressor blades of the Nos. 1 and 2 engines, as well as to the No. 4.

Within weeks of the latest event, Boeing and General Electric flight tested an engine software upgrade specifically designed to counter the ice-crystal buildup. GE says the software changes to the GEnx-2B full-authority digital engine-control unit will help the engine itself detect the presence of ice crystals when the aircraft is flying through a convective weather system. If detected, the new algorithms will schedule variable bleed valves to open and eject ice crystals that may have built up in the area aft of the fan, or in the flowpath to the core. The modification to the GEnx control logic leverages similar changes made to improve the ability of the CF6 to operate in similar icing conditions.

Avweek

The entire icing issue is a fascinating and amazing read. It really underscores that while we've come so far so fast in relation to flight, there is so much that we still don't understand that can kill us in the blink of an eye.