SWA1380 - diversion to KPHL after engine event
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Because she felt it was not needed. If you listen to the ATC recordings, she stayed exactly within the limits of her authority without getting "trigger happy".
She initiated her descent and subsequently informed the controller (aviate, navigate, communicate). By doing that she used her authority provided by 14 CFR 91.3b, and exactly by that rule: she only deviated from her previous clearance to the extent necessary (emergency descent).
She then asked for directions to the nearest suitable airport. At that point, the controller was perfectly aware of the situation and there really was no need to explicitly declare an emergency.
But, even so: if needed a controller can "declare an emergency" for you. In reality it was not needed, since no rules needed to be breached. If, for example, she had to fly through restricted airspace to get to the runway, then explicitly declaring an emergency may have made sense. But even in that case: no FAA official is going to question her actions.
You declare an emergency to get the attention you need. If you already have the attention, it's just a waste of brain cycles and precious communication time.
She initiated her descent and subsequently informed the controller (aviate, navigate, communicate). By doing that she used her authority provided by 14 CFR 91.3b, and exactly by that rule: she only deviated from her previous clearance to the extent necessary (emergency descent).
She then asked for directions to the nearest suitable airport. At that point, the controller was perfectly aware of the situation and there really was no need to explicitly declare an emergency.
But, even so: if needed a controller can "declare an emergency" for you. In reality it was not needed, since no rules needed to be breached. If, for example, she had to fly through restricted airspace to get to the runway, then explicitly declaring an emergency may have made sense. But even in that case: no FAA official is going to question her actions.
You declare an emergency to get the attention you need. If you already have the attention, it's just a waste of brain cycles and precious communication time.
Sure follow the mantra Aviate Navigate - but you are in one of the busiest airspaces in the CONUS - if you do not communicate you may add TCAS RAs and worst case a collision to your bad day. A simple 7700 solves all of that and tells everyone that you have a problem.
For those of you that care, current ATC systems will maintain your identity but add symbology that shows you have an emergency on controller displays.
7700 is the same for MAYDAY or PAN so it removes the dialectic nuances of is it really a MAYDAY or only a PAN and with modern surveillance systems is far more effective than an R/T call.
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I think the main issue is that the blade (due to being weakened by the fatigue crack) started to bend and rotate forward and did not break away clean to an explosion, like during the test. How many degrees it rotated forward before failing is something that needs to be analysed and might mean we need to rethink containment requirements.
1. A fan blade that "rotates forward" will almost immediately result in a blade tip/case strike. The resulting forces acting on the blade will cause the blade to fail at the fatigue crack.
2. What would cause the fan blade to "rotate forward"? The fan is a compressor section. In other words, in a turbo fan engine the fan blade compresses the air, it does not accelerate the air like a propeller. Further, the huge tension forces resulting from the massive centripetal acceleration of the blade will overwhelm any aero force pushing on the blade. Consider a guitar string. It is under considerable tension. Can you blow on the string to cause it to bend? No. The tension on the fan blade is several orders of magnitude greater than the tension on the guitar string.
Last edited by KenV; 20th Apr 2018 at 13:08.
OK. Let's try this: the Newtonian physics associated with the air acting on a separated fan blade are completely overwhelmed by the Newtonian physics of the moments of inertia acting on the blade. Kinda like a bullet in air-to-air combat. Sure, aerodynamics will affect the bullet's ballistic trajectory. But those affects are overwhelmed by the moments of inertia acting on the bullet.
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7700 is the same for MAYDAY or PAN so it removes the dialectic nuances of is it really a MAYDAY or only a PAN and with modern surveillance systems is far more effective than an R/T call.
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Listening to the tapes. All she said was she was single engine and descending. No mention of an emergency descent due to decompression. From what she said I would assume the controller would assume a gentle descent down to single engine ceiling.
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The most important data the computer needs to know about each blade is not its weight, but its moment of inertia relative to the rotor axis,
And I would assume that when you do these inspections, the easiest way is in fact to just number the blades and their position on the disk with a permanent felt-tip marker.
Bernd
And I would assume that when you do these inspections, the easiest way is in fact to just number the blades and their position on the disk with a permanent felt-tip marker.
Bernd
In fact each blade has a serial number and each position on the rotor is numbered, thats how it was tracked.
Nice explanation, Ken, and I agree with Dave about the trajectory analogy. Once that projectile leaves the barrel it doesn't make any difference what body rates and such were.
OTOH, Dave, I think the moments are very important as to where the blade breaks, especially if the density of the thing changes as you go from hub to tip.
Glad to hear that inspections are not as big a deal as I thot. NDI gear and procedures have changed dramatically since I got outta the business, just like medical equipment.
Gums..
P.S. I had severe fan blade destruction one day on my PW F100 after a chunk off ice came off the intake soon after takeoff. Had 60 -70 blades severely bent and many with large sections missing. Good thing about fans is a lotta debris goes around the core and only really big pieces leave "containment" We saw that with the TF-41 in the Sluf, as well, with bird strikes.
OTOH, Dave, I think the moments are very important as to where the blade breaks, especially if the density of the thing changes as you go from hub to tip.
Glad to hear that inspections are not as big a deal as I thot. NDI gear and procedures have changed dramatically since I got outta the business, just like medical equipment.
Gums..
P.S. I had severe fan blade destruction one day on my PW F100 after a chunk off ice came off the intake soon after takeoff. Had 60 -70 blades severely bent and many with large sections missing. Good thing about fans is a lotta debris goes around the core and only really big pieces leave "containment" We saw that with the TF-41 in the Sluf, as well, with bird strikes.
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Well, it depends on your frame of reference. Since the blade is attached to the hub and the hub is spinning at a high rate, I used the term moment of inertia. Further, in my bullet analogy, a bullet is spinning at a very high rate which stabilizes it. Nevertheless, once the blade fails and detaches from the hub, the blade is behaving under plain inertia, and with no spin to stabilize it. So in that sense, you are correct and I concede your point.
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There's something that puzzles me.
All over the Planet Earth it's being mentioned Mrs. Tammie Jo Shults as "the hero pilot, bla, bla,bla".
But listening to the radio exchange (brief and complete ones) between ATCs, TWR & AC, there's one thing very clear: THE PIC DURING ALL THE DESCENT WAS F.O. Mr. Darren Ellisor.
Mrs. Shults was in charge of radio and -surely- checklists while Mr. Ellisor was PIC descending and later aligning for a visual long final.
I've got not clear if Mr. Ellisor was PIC at the moment of the engine failure.
All over the Planet Earth it's being mentioned Mrs. Tammie Jo Shults as "the hero pilot, bla, bla,bla".
But listening to the radio exchange (brief and complete ones) between ATCs, TWR & AC, there's one thing very clear: THE PIC DURING ALL THE DESCENT WAS F.O. Mr. Darren Ellisor.
Mrs. Shults was in charge of radio and -surely- checklists while Mr. Ellisor was PIC descending and later aligning for a visual long final.
I've got not clear if Mr. Ellisor was PIC at the moment of the engine failure.
Last edited by guadaMB; 20th Apr 2018 at 16:30. Reason: Typo
guada,
It doesn't matter who was the handling pilot at the time of the incident. But good cockpit management (CRM) suggests that the captain should manage the situation while the copilot handles the aircraft. This allows the captain to have time to think, generally oversee the whole operation, do the R/T and run the checklists.
From what I heard of the ATC tape that is what seems to have happened. As to who does what and when, that is solely up to the captain - who remains in control of the whole conduct of the flight.
It appears to have been a good job very well done. Not hero stuff, but good professional competence.
It doesn't matter who was the handling pilot at the time of the incident. But good cockpit management (CRM) suggests that the captain should manage the situation while the copilot handles the aircraft. This allows the captain to have time to think, generally oversee the whole operation, do the R/T and run the checklists.
From what I heard of the ATC tape that is what seems to have happened. As to who does what and when, that is solely up to the captain - who remains in control of the whole conduct of the flight.
It appears to have been a good job very well done. Not hero stuff, but good professional competence.
In fact its even more clever than that. When visiting BAs maintenance facility, i was shown what the do on a/c during a C check.
The blades are taken out and inspected an weighed, thats fed into a computer and it defines the optimal position for each blade being put back to achieve the best balance.
The blades are taken out and inspected an weighed, thats fed into a computer and it defines the optimal position for each blade being put back to achieve the best balance.
I’d question the advisability of changing matched pairs in the interest of balancing the disc?
There's something that puzzles me.
All over the Planet Earth it's being mentioned Mrs. Tammie Jo Shults as "the hero pilot, bla, bla,bla".
But listening to the radio exchange (brief and complete ones) between ATCs, TWR & AC, there's one thing very clear: THE PIC DURING ALL THE DESCENT WAS F.O. Mr. Darren Ellisor.
Mrs. Shults was in charge of radio and -surely- checklists while Mr. Ellisor was PIC descending and later aligning for a visual long final.
I've got not clear if Mr. Ellisor was PIC at the moment of the engine failure.
All over the Planet Earth it's being mentioned Mrs. Tammie Jo Shults as "the hero pilot, bla, bla,bla".
But listening to the radio exchange (brief and complete ones) between ATCs, TWR & AC, there's one thing very clear: THE PIC DURING ALL THE DESCENT WAS F.O. Mr. Darren Ellisor.
Mrs. Shults was in charge of radio and -surely- checklists while Mr. Ellisor was PIC descending and later aligning for a visual long final.
I've got not clear if Mr. Ellisor was PIC at the moment of the engine failure.
“The industry took no major issue with the 2017 proposal, though some airlines requested longer compliance times. They said the rule would affect more than 220 engines because airlines often swap blades between engines.“
Fan balance is very important for the CFM56 on the 737 - the engine is so close coupled with the wing that any fan imbalance will cause annoyingly high vibrations in the passenger cabin.
But the main point is that if an operator has 10 engines that would be affected by the AD, the fan blades originally from those engines might be spread around many more than 10 engines.
<edited to address Concours 77>
While there will always be a small amount of wear between the blade dovetail and the hub, special coatings and lubes are used to limit the wear, and there are strict limits on the allowable amount of wear (it's not much - a few thousands).
However, having been involved in several FAA AD's over the years, 8 months and it's still not released is inexcusable. AD's by definition affect flight safety. Normal flow time for a 'routine' AD is a couple months - seldom going much beyond 3 months even if there are lots of comments (emergency AD's don't go through public comment and can go out in a few days). While getting the blade inspection AD released may not have affected this accident, it's pretty clear to me that someone in the FAA dropped the ball.
However, having been involved in several FAA AD's over the years, 8 months and it's still not released is inexcusable. AD's by definition affect flight safety. Normal flow time for a 'routine' AD is a couple months - seldom going much beyond 3 months even if there are lots of comments (emergency AD's don't go through public comment and can go out in a few days). While getting the blade inspection AD released may not have affected this accident, it's pretty clear to me that someone in the FAA dropped the ball.
However both the manufacturer and the FAA have processes developed under continued airworthiness rules to assess in-service experience coupled with today's analysis. Such experience includes probable causes and population at risk, (of a blade fracture) certification basis, and any unexpected in-service additional safety concerns beyond a safe engine shutdown.
The risk analysis does consider a given that a blade fracture will occur sometime in the future, but given such a fracture other combinations of risk in the in-service experience ala crew error or parts being liberated beyond the engine itself (possibly some others that I can't remember at this time)
In the end such analysis need show that the risk of a far more serious event than currently experience in the data must be extremely low and not significantly contribute to the underlying risk of flying that product in its expected lifetime.
It does not mean that a simple blade fracture will not occur while they are dotting the "Is" and crossing the "Ts" in a proposed AD but based on data available nobody close to this would have expected the result in this flight.
OK it is obvious that an unexpected combination did occur and the AD does have to be adjusted. So let's just get after this bottom line lest we end up only blaming somebody instead.
However both the manufacturer and the FAA have processes developed under continued airworthiness rules to assess in-service experience coupled with today's analysis. Such experience includes probable causes and population at risk, (of a blade fracture) certification basis, and any unexpected in-service additional safety concerns beyond a safe engine shutdown.
Think of it this way - the risk assessment said they could allow 12 months to do the inspections without a significant safety threat - but they'd already used up over half of that and still hadn't mandated the inspections. So the safety assessment would have to be for at least 20 months which would most likely change the answer.
Knowing and having worked with the FAA for 2/3rds of my career, I'd bet pretty good money the AD's been sitting in someone's in-basket - forgotten - for several months. I'd bet even more money that the responsible person or persons will get nothing worse than a wrist slap.
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emergency inspection called for
Airline Regulators Call for Emergency Inspections of Boeing 737 Engines
Regulators expected to require inspections sooner, and of more engines, than previously proposed
Regulators expected to require inspections sooner, and of more engines, than previously proposed
By Andy Pasztor, Doug Cameron and Robert Wall
Updated April 20, 2018 4:17 p.m. ET 0 COMMENTS
U.S. aviation regulators in the wake of this week’s fatal Southwest Airlines Co. accident are expected as soon as today to impose emergency inspection requirements for certain jet engines going beyond what they previously proposed, according to people familiar with the issue.
Updated April 20, 2018 4:17 p.m. ET 0 COMMENTS
U.S. aviation regulators in the wake of this week’s fatal Southwest Airlines Co. accident are expected as soon as today to impose emergency inspection requirements for certain jet engines going beyond what they previously proposed, according to people familiar with the issue.
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Further, the huge tension forces resulting from the massive centripetal acceleration of the blade will overwhelm any aero force pushing on the blade.
There is no substantial difference between an axial compressor, fan, and propeller. They all apply a rearward force on air, and therefore the air applies a forward force on the blade.
