Warning: mysql_real_escape_string(): Access denied for user 'brokenwi'@'localhost' (using password: NO) in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): A link to the server could not be established in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): Access denied for user 'brokenwi'@'localhost' (using password: NO) in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): A link to the server could not be established in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): Access denied for user 'brokenwi'@'localhost' (using password: NO) in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): A link to the server could not be established in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): Access denied for user 'brokenwi'@'localhost' (using password: NO) in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): A link to the server could not be established in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): Access denied for user 'brokenwi'@'localhost' (using password: NO) in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): A link to the server could not be established in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): Access denied for user 'brokenwi'@'localhost' (using password: NO) in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786

Warning: mysql_real_escape_string(): A link to the server could not be established in /home/brokenwi/public_html/wp/wp-content/plugins/statpress-reloaded/statpress.php on line 1786
Compressor Stall on earlier US Airways Flight 1549 (2 days before Hudson Crash) | Broken Wing

Compressor Stall on earlier US Airways Flight 1549 (2 days before Hudson Crash)

Posted on 20. Jan, 2009 by in Featured

Wow, it sure didn’t take long for the press to try and turn good news bad. That is their nature I suppose, bad news sells in their opinion. First, a note in the headline explaining it was the same aircraft would have been appropriate (it was according to the NTSB).

The fact it has nothing to do with losing both engines due to severe damage caused by bird ingestion might be a nice little note as well, but let’s charge with the uneducated pack for a minute or two. What is a compressor stall? Here is the definition according to the NTSB:

“Most in-flight shutdowns are benign and likely to go unnoticed by passengers. For example, it may be prudent for the flight crew to shut down an engine and perform a precautionary landing in the event of a low oil pressure or high oil temperature warning in the cockpit. However, passengers may become quite alarmed by other engine events such as a compressor surge– a malfunction that is typified by loud bangs and even flames from the engine’s inlet and tailpipe. A compressor surge is a disruption of the airflow through a gas turbine engine that can be caused by engine deterioration, a crosswind over the engine’s inlet, ingestion of foreign material, or an internal component failure such as a broken blade. While this situation can be alarming, the condition is momentary and not dangerous.”

They can be quite loud; a few months back an aircraft I was flying had a series of compressor stalls and we heard it in the cockpit, 80 feet or so forward. We pulled the throttles back and they stopped, and then we looked for secondary indications. You can clear compressor stalls and if no other problems are apparent and it is permissible by the engine manufacturer and company policy continue on. In our case there were secondary’s (engine instruments not correct) so we came back and landed.

What is a compressor? Below is a basic depiction:

turbojet

The bullet shaped blue center is the actual compressor. It has blades of decreasing lengths that pull air into the compressor section jam it through a diffuser and into the combustion chamber. The fuel control meters fuel into the burner cans and igniters light it. The pressure differential continues to move aft through the turbine section, which is connected by drive shafts to the compressor section. The pressure pushes through the turbine blades (which spins them and due to the drive shaft the compressor blades as well pulling in more air), out the tail comes thrust. The chain reaction will continue under normal circumstances until the fuel runs out.

turbofan

The top diagram is a turbo-jet engine (old fuel hogs), the second diagram is a modern turbo fan. Notice the first blue stage (in front of compressor section); it is an oversized set of blades that produce a lot more thrust because it uses by-pass. The fan stage produces more air than the engine can swallow (too much and it will compressor stall); so it is vented around the outside of the engine and used as thrust. It is a much more fuel efficient arrangement. The by-pass ratio on modern engines can be as much as 85%.

Normal circumstances do not include a dog sized bird, or more than one, going down the engine and smashing the blades. The old turbo-jet engines (F-4 Phantom II, A-4 Sky hawk, A-6 Intruder) could be taken out with a paper clip, because all the air was contained and went down the engine. They are like giant vacuum cleaners. Another advantage of turbo-fan engines is that the high by-pass stage throws FOD (foreign object damage) clear of the internal engine. Even small birds, ice, etc; so if that stage gets FOD’d and causes compressor stalls the internal engine will most likely stay intact. Airlines utilize turbo-fan engines so losing one to FOD is unusual. Losing two is extremely rare!

Let’s look at a more descriptive presentation of an engine, look particularly at the blades:

turbofan-detailed

If a large object (goose) slams into the first set of blades a chain reaction follows causing all the blades to break sequentially, stopping the chain reaction of compression/combustion/thrust. The engines stop. A goose is just too big to be exhausted through the by-pass.

So an engine compressor stall that cleared and was examined by maintenance two days prior had NOTHING to do with geese destroying the engines. The press will run with this for days; they may even uncover an un-dotted i or un-crossed t. But in the end it will have nothing to do with that aircraft going into the river. Our society has grown weak, we must always find blame, and we just can’t come to grip the fact that sometimes bad things happen that cannot be prevented. “Someone must be at fault!” besides it sells newspapers and airtime.

3 Responses to “Compressor Stall on earlier US Airways Flight 1549 (2 days before Hudson Crash)”

  1. Tadick Margach 20 January 2009 at 15:24 #

    I Have Retired now after 50 years as licenced Engineer.I found that the old JT8D Engines were susseptible to Compressor Stalls including onces during T/O the Engine ingesting a News Paper the T/O was aborted I Inspected the Engine I/aw M.Manual and found no damage.These Engines took a lot before they were Unserviceable.Yet the Modern CFM56 engnes Due to large Fan design suffer mechinical damage from a compressor stall and have to be removed from service as recommended by the Manufacturers.Also these Blades design profile are far more complex and more easily affected.

  2. Tadick Margach 20 January 2009 at 15:24 #

    I Have Retired now after 50 years as licenced Engineer.I found that the old JT8D Engines were susseptible to Compressor Stalls including onces during T/O the Engine ingesting a News Paper the T/O was aborted I Inspected the Engine I/aw M.Manual and found no damage.These Engines took a lot before they were Unserviceable.Yet the Modern CFM56 engnes Due to large Fan design suffer mechinical damage from a compressor stall and have to be removed from service as recommended by the Manufacturers.Also these Blades design profile are far more complex and more easily affected.

  3. Chip 21 January 2009 at 18:45 #

    Tadick;
    I agree the old turbojet engines “popped” all the time. When I was flying the EA-6B Prowler on board various ships they were powered by J52-P408 turbojets. They compressor stalled all the time, it was usually “water in the traps” according to our mechanics.

    They were also tougher, popping didn’t bother them at all. In fact I remember when an A-4F was taking off one day he had forgotten to shift the fuel control unit back to auto after checking the manual back up mode. When he jammed the throttle forward it shot 30 foot flames out of both ends. He taxied it back to the line and shut down. It was still running. You could actually see through it end to end.


Leave a Reply