Plane damaged by hail makes emergency landing

Sep 8, 2014
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Norman, OK
I just flew out of the Denver to Milwaukee last night. I saw those storms off to the east and they looked great on radar and in person. Aren't pilots supposed to fly around the storms with bad hail cores? My plane went through these same storms later but they had transitioned to a MCS so the threat of hail was low. Anyways, I'm glad I didn't see this article until now because I get very nervous about flying.
 

Jeff Duda

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Ummm...yeah, that seems like quite the expensive oversight or error on the part of someone, probably the pilots, or perhaps a meteorologist who was watching the area. Pretty sure commercial planes are not supposed to fly directly into storms, or even near them. I've been on flights before where the flight path was very obviously diverted around storms. Granted, I've also landed at Omaha coming out of the bottom of a weak thunderstorm before, too. I wonder if there was a malfunction with the plane's radar (or if it even had one).
 
It did have radar, because news reports indicate that much of the damage was to the radome in the nose. But of course that would not have happened until it had already flown into the storm, so I have no idea why the flight crew did not divert the flight path around the storm. Indeed, I have also been wondering why they did not.
 
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A few years ago I was on a September non-stop from JFK to Denver that took off right around dusk. As we ascended there was an MCS/MCC approaching that was only about 10 miles to the west with lots of lightning. The rest of my party, flying from JFK to Ohio, spent the night in NYC because my flight was one of the last to depart. Equipped with those screens that display our flightpath, I watched as we flew north of Toronto before finally turning west through the Dakotas to get to Denver. Despite going around the huge system we still had bad turbulence the entire flight, even as we descended in Colorado.

Another memorable thing I've seen was at Denver on May 26, 2010. That was the day of a surprise (to me, anyway!) tornado at the Denver airport, which was filmed by a worker at the airport looking straight up, but that's not the reason for me to post this. The thing that really got me was watching a Southwest Airlines plane taking off right under the RFB. I don't remember if the tornado was ongoing at that exact moment or not, but it was right around that time.
 

Kendra Sand

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Jun 9, 2015
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I'd be interested to know if there was a SIGMET out at the time. The Delta Airlines meteorologists in Atlanta are among the top mets in the world (so I've heard), so I really doubt that they were caught off guard by these storms, but not impossible mind you. Was there a lapse in communication, or was the aircrew fully aware of storms in the area? Normally the radar approach controllers would vector the aircraft safely around the storms, or at least the most threatening areas. And the cockpit is equipped with a crude version of radar that is supposed to show generally what spots to avoid.

Don't get me wrong, I'm not trying to assign blame at all... we will have to wait and see what the FAA investigators find out. But I will say this, pilots have been known to push the limits at times, and it would be the captain's prerogative to do so if he felt it was safe enough to fly straight through. (And unfortunately, that leaves a lot of responsibility on the shoulders of the pilots. So if the FAA can't find anything mechanically wrong or an error on the part of the operations team, the blame usually defaults to the pilot in command. It could very likely lead to the captain's license being revoked.) Nevertheless, it's amazing and a credit to the pilots' skill that they were still able to land safely. Thank God for that!
 
Mar 30, 2008
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Interesting to see that they tried to basically get between two storms and had an updraft blow up in their path. Expensive mistake, for sure.

Knowing how hail gets louder the bigger it is and the faster you drive, can you imagine how loud it had to be going a few hundred miles an hour having big hail ping off the airplane? That had to rock!
 

Jeff Duda

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Looks more to me like they just picked a path long before getting to the incident area and frankly, missed. I would think they would've had time to update their path and curve west rather than WSW just as they saw the precip starting to cover their originally intended path.
 

Jeff Duda

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BTW, Iet's talk about those descent rates.

The original article says the plane droppsed 14 kft over a two-minute span. Taking that literally, that's an average descent rate of , 116.7 ft/s or 79.5 mph. Pretty fast. But the twitter post embedded in the blog says the plane descended 12 kft in about one minute, for an average rate of 200 ft/s, or 136 mph! I'm pretty sure the terminal velocity (assuming no pitch, yaw, or nose tilt on the plane) is less than that. That's also faster than even large hailstones would fall. That makes it seem like the plane was probably significantly nose down during a portion of that dive. To accelerate to those speeds would probably have lifted some people out of their seats if they weren't belted. Maybe not, but that's still some extreme speed.
 
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I wouldn't imagine the plane would have been able to be nose down at those speeds and remain intact. That would have been a huge overspeed, even with the wind pushing it down I think. Not sure the airframe could handle that.
 

Jeff Duda

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Okay, I see in the Twitter feed regarding the one tweet in the blog post SMOK linked to that the estimation of 12 kft in 1 min was not timed, so it probably occurred over a longer span of time.
 
Don't forget about turbulence. My dad used to be a navigator on B52s (a rather large airplane). On day, while flying over some mountains in the middle of a storm, his plane dropped over 5,000 feet in a few seconds. Yes, everything in the cabin not held down hit the top of the plane. The cause of this large and sudden drop was a large downward flow of air from the thunderstorm combined with a large downward flow of air from the backside of the mountain. You'll never hear about a drop this fast from a commercial airplane though, because they tend to avoid mountains and thunderstorms for this reason.

The speed of an airplane is relative to the air around it. That is why airplanes use two speeds: air speed and ground speed. If an airplane encounters a 100kt tail wind, the air speed might be 150kts while the ground speed is 250kts. The air speed, not the ground speed, is what a pilot uses to determine a plane's actual speed (for the purposes of structural integrity [most important while the landing gear is lowered], and fuel consumption). The ground speed is used for navigation purposes (such as determining an estimated time of arrival).

The same difference between air speed and ground speed goes for vertical air flow as well. Planes cruise at a vertical air speed of 0kts (maintaining altitude). Normally, air flow does not deviate much in a vertical direction. But near mountains and in thunderstorms, air moves in a vertical direction. So if the air flow relative to the ground is moving 100kts downward (toward the ground), an airplane that encounters this vertical airflow (a.k.a. turbulence) would lose altitude at a speed of 100kts relative to the ground. But it's vertical air speed relative to the air around it would still be 0kts.

So for those of you considering the terminal velocity of the airplane or saying that 12,000 ft in a minute is not possible, just remember that relative to the air around the airplane, the airplane was not moving downward at all and in fact was maintaining altitude. But relative to the ground, the airplane lost altitude.

Anybody who knows more about airplanes than I do, feel free to correct me or expand. This is my understanding of how airplanes work based upon my dad's experience. I know there is at least one pilot on this site that can correct me or explain better.
 

MClarkson

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http://flightaware.com/live/flight/DAL1889/history/20150807/2130Z/KBOS/KDEN/tracklog

The flightaware track is pretty clear: The aircraft descended at the reasonable rate of about 2000 feet per minute. This was an intentional descent initiated after the hailstorm. The aircraft had to descend into Denver and it would be quite reasonable to distrust the integrity of ones windshields after that. I don't know where the 12,000 fpm quote started, but like most generic media reports on aviation, is clearly wrong.
 
OK, obviously the aircraft in this article did not descend as fast as the media reported. But it is possible for an aircraft to descend that fast...

http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/ComAndRep/ChinaAir/AAR8603.html

According to this accident report, in 1985 a commercial airliner descended at a rate of 18,745 feet per minute. The aircraft experienced a peak force of 5.1G, causing damage to the plane. The plane landed safely and amazingly only 2 people were seriously injured and there were no fatalities.

"Between 1014:50 and 1015:23, the DFDR recorded a 10,310-foot descent to 30,132 feet." -- That's a 10,310 foot descent in only 33 seconds.

"Between 1015:23 and 1017:15, the airplane descended from 30,132 feet to 9,577 feet." -- That's a 20,555 foot descent in only 1 minute and 52 seconds.
 

MClarkson

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Sep 2, 2004
892
27
11
Blacksburg, VA
Man, that is quite a plunge(Scotts link, not the DAL A320). 5.1G pulling out of that dive? In a 747. Good thing Boeing makes good planes. Transport planes are regulated only up to 3.8G if I remember correctly. Look at that horizontal stabilizer!