Bird strike out of Guernsey continues on one Engine to Birmingham
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Yes Flybymike, I do recall the accident you mention. It was KLM Flight 433, a Saab 340B.
PROBABLE CAUSES: "Inadequate use of the flight controls during an asymmetric go around resulting in loss of control.
Contributing factors: Insufficient understanding of the flight crew of the SAAB 340B engine oil system; lack of awareness of the consequences of an aircraft configuration with one engine in flight idle; poor crew resource management."
PROBABLE CAUSES: "Inadequate use of the flight controls during an asymmetric go around resulting in loss of control.
Contributing factors: Insufficient understanding of the flight crew of the SAAB 340B engine oil system; lack of awareness of the consequences of an aircraft configuration with one engine in flight idle; poor crew resource management."
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Engine shutdown?
I'm late catching up to this thread, but 7 pages in, I'm still wondering - what makes you all think that the Captain shut down the engine? I'm not familiar with the Dash 8, but I have flown other P&W turboprops, and as far as I know they are all free-spool power stages. On many (all?) you can feather the propeller completely in flight without shutting down the engine, leaving the engine at idle. I know that the passengers were told "as a precaution we are going to shut down the left engine", but that's what I would have said on the PA too, even if I was leaving the engine running and just feathering the prop. It's too hard to explain it any other way when the propeller is quite clearly stationary.
Meanwhile, since the hit was the "lucky shot" right on the spinner, I imagine the only symptom on the flight deck was a "thump" on the climb-out. With all the T's and P's in the green, both engines turning just fine, of course you keep going - fly the SID, get up into the cruise. Then (20 minutes into the flight) the F.O. went back to see if there was anything to see, returned and said "we've lost a huge chunk of the spinner". They decide to feather the prop to limit any further damage, but carry on because there's nothing obviously broken - and if my guess is right, both engines are still running. If the worst comes to happen, they can always unfeather the one with the broken spinner and get back to two. No relight required.
So - anyone here flown a Dash 8? Can you feather the prop with the engine running?
Meanwhile, since the hit was the "lucky shot" right on the spinner, I imagine the only symptom on the flight deck was a "thump" on the climb-out. With all the T's and P's in the green, both engines turning just fine, of course you keep going - fly the SID, get up into the cruise. Then (20 minutes into the flight) the F.O. went back to see if there was anything to see, returned and said "we've lost a huge chunk of the spinner". They decide to feather the prop to limit any further damage, but carry on because there's nothing obviously broken - and if my guess is right, both engines are still running. If the worst comes to happen, they can always unfeather the one with the broken spinner and get back to two. No relight required.
So - anyone here flown a Dash 8? Can you feather the prop with the engine running?
You sure can feather the propeller without shutting down the turbomachinery - this is commonly done during every shutdown (it takes 30 seconds from feather before the engine may be shut down due to cooling). There are some abnormal procedures as well that call for feathering only, not shutting the engine down inflight.
A running engine will keep on spinning a feathered prop. On the DH8D, approximately 220 rpm are expected. While the look of a propeller in such a state is certainly different from a normally running example, it is most definitely not stationary.
However, on the incident in question, I strongly doubt the engine was left running.
Firstly, it would take quite a coincidence for a birdstrike to shave off the spinner that cleanly without causing any temporary imbalance. Disintegration of the spinner must come with a few seconds worth of strong vibrations while parts break off unevenly. Also, it is not unlikely that some parts hit the fuselage (in the area of the ice impact trays).
Secondly, the forward 2/3 of the spinner are visible from the flight deck. It does not take a trip to the cabin to find the spinner gone - just turning back and looking out will do the trick; at night, the wing inspection lights will come in handy. So if after a noticeable airframe shudder, the Captain finds the spinner no longer visible from the flight deck, the assumption of serious engine damage, possibly with ingestion of debris, may well be made. This in turn calls for one of the likely best known checklists on this aircraft (from the simulator, I should add): "Engine failure or severe damage after V1" and will result in a full shutdown.
So I think it most unlikely that the colleagues decided to run the engine feathered in such a condition instead of properly securing it.
Originally Posted by CJ Driver
...when the propeller is quite clearly stationary.
However, on the incident in question, I strongly doubt the engine was left running.
Firstly, it would take quite a coincidence for a birdstrike to shave off the spinner that cleanly without causing any temporary imbalance. Disintegration of the spinner must come with a few seconds worth of strong vibrations while parts break off unevenly. Also, it is not unlikely that some parts hit the fuselage (in the area of the ice impact trays).
Secondly, the forward 2/3 of the spinner are visible from the flight deck. It does not take a trip to the cabin to find the spinner gone - just turning back and looking out will do the trick; at night, the wing inspection lights will come in handy. So if after a noticeable airframe shudder, the Captain finds the spinner no longer visible from the flight deck, the assumption of serious engine damage, possibly with ingestion of debris, may well be made. This in turn calls for one of the likely best known checklists on this aircraft (from the simulator, I should add): "Engine failure or severe damage after V1" and will result in a full shutdown.
So I think it most unlikely that the colleagues decided to run the engine feathered in such a condition instead of properly securing it.
TU.114
What would shutting off the fuel to the engine actually do to any of the symptoms available to the pilot?
Does not the prop continue to spin slowly even with the engine shut down?
No withstanding the tenths of seconds of imbalance as the spinner tears away doesn't the final imbalance seem very small considering it's small relative diameter compared to the prop?
Not being there and not seeing the actual symptoms displayed I'm wont to predict what the pilots actually did.
So I think it most unlikely that the colleagues decided to run the engine feathered in such a condition instead of properly securing it.
Does not the prop continue to spin slowly even with the engine shut down?
No withstanding the tenths of seconds of imbalance as the spinner tears away doesn't the final imbalance seem very small considering it's small relative diameter compared to the prop?
Not being there and not seeing the actual symptoms displayed I'm wont to predict what the pilots actually did.
I agree - it is impossible to say "it has been thus" until an investigation report is out. This is why I wrote "unlikely", not "certainly not".
But just for discussion purposes and beyond the scope of this incident:
A feathered propeller with its engine shut down is expected to stand still - it might move momentarily, but nowhere near the mentioned 220rpm of a feathered, but still driven propeller and even way farther from the 850rpm of a thrust-producing one in cruise (numbers for DH8D). The centrifugal force induced by an off-center, unbalanced object, such as the bird carcass that remained in the spinner is F=m ω² r. M and r is constant; at 2 rpm the figure for ω² is 0,04; at 220rpm 530 and at 850rpm 7923 - the force creating an imbalance obviously rises proportionally to this figure.
In case this is true, there must have been noticeable and certainly abnormal persistent vibration caused by this damage while the engine still was running. The "Engine Failure/Severe damage" checklist is definitely applicable in this case and will lead to an engine shutdown.
If the spinner was just dumped without any persistent vibration, it certainly is a case-by-case decision to be made on the other hand.
But just for discussion purposes and beyond the scope of this incident:
A feathered propeller with its engine shut down is expected to stand still - it might move momentarily, but nowhere near the mentioned 220rpm of a feathered, but still driven propeller and even way farther from the 850rpm of a thrust-producing one in cruise (numbers for DH8D). The centrifugal force induced by an off-center, unbalanced object, such as the bird carcass that remained in the spinner is F=m ω² r. M and r is constant; at 2 rpm the figure for ω² is 0,04; at 220rpm 530 and at 850rpm 7923 - the force creating an imbalance obviously rises proportionally to this figure.
In case this is true, there must have been noticeable and certainly abnormal persistent vibration caused by this damage while the engine still was running. The "Engine Failure/Severe damage" checklist is definitely applicable in this case and will lead to an engine shutdown.
If the spinner was just dumped without any persistent vibration, it certainly is a case-by-case decision to be made on the other hand.
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Fair enough TU.144, thanks for the type specific info. I confess I am surprised at the 220 RPM though. On our turboprop, feathering the prop with the engine running gave a lazy "hardly turning at all" effect, especially in level cruise, where the propeller really would stop - presumably because the airflow over the blades completely overcame the residual torque on the power turbine. If you slowed down, the prop would start slowly turning again. At the other extreme (stationary on the ground with the propeller feathered) it would go around at a fair clip - but even then I'm not sure it was 220 rpm.
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Tu144
The RPM you mention. That seems to be likely stationary on the ground but unlikely in flight. Have you actually seen that rotation feathered in flight with the engine still running?
Like Cj driver, I have found most to be nearly stationary feathered in flight with the engine still running though I have not flown the Dash.
The RPM you mention. That seems to be likely stationary on the ground but unlikely in flight. Have you actually seen that rotation feathered in flight with the engine still running?
Like Cj driver, I have found most to be nearly stationary feathered in flight with the engine still running though I have not flown the Dash.
I have not yet had an engine quit in flight, so I cannot provide any first hand experience here. However, in the simulator, 200-220rpm have been observed in flight with a feathered propeller driven by an idling engine. Also, our documentation is rather clear about this; it contains the following figures as an aid to determine the state of a malfunctioning engine/propeller assembly:
- engine running, propeller feathered: 200rpm
- engine dead, propeller feathered: 0 rpm
- engine dead, propeller unfeathered: above 0 rpm; the sim shows about 150-170 rpm constantly in this condition after a V1 cut
So I have no reason to assume that a feathered propeller will not be spun by a still running engine. Another thought: A running engine provides a few percent of torque. Were the propeller to stand still despite this, the torque would have to be countered by something. That "something" can only be aerodynamic force; likely created by airflow interacting with the feathered prop blades. Assuming this to be true, what happens when one shuts down the gas generator? The engine provides no more torque, but the aerodynamic forces in the opposite direction are still there. So the propeller would start to spin in the direction opposite to its normal operation.
On the DH8, this is definitely not the case. Is it on Your type? If not, is a prop brake installed and activated in such a situation?
- engine running, propeller feathered: 200rpm
- engine dead, propeller feathered: 0 rpm
- engine dead, propeller unfeathered: above 0 rpm; the sim shows about 150-170 rpm constantly in this condition after a V1 cut
So I have no reason to assume that a feathered propeller will not be spun by a still running engine. Another thought: A running engine provides a few percent of torque. Were the propeller to stand still despite this, the torque would have to be countered by something. That "something" can only be aerodynamic force; likely created by airflow interacting with the feathered prop blades. Assuming this to be true, what happens when one shuts down the gas generator? The engine provides no more torque, but the aerodynamic forces in the opposite direction are still there. So the propeller would start to spin in the direction opposite to its normal operation.
On the DH8, this is definitely not the case. Is it on Your type? If not, is a prop brake installed and activated in such a situation?
