Delta Airlines pilots make blind emergency landing after hailstones crack windscreen

[tigermonkey]

However hail does NOT show on the radar and it rarely falls within the thunder cell. Hail falls from the anvil at 50 - 60,000 feet and usually falls outside the thunder cell ( the cloud) due to wind drift. There is seldom any warning of being hit by hail, and it has even been known in what is apparently clear air. THERE IS NO WAY TO AVOID HAIL .

Firstly I don't know much about weather radar as I never flew an aircraft with it. If you google "Optimum use of the weather radar" you get a paper in the Airbus library. On page 2 it states

"Above FL 200, hail is most likely to be encountered inside the cloud" (Cb)

The graphic on the page shows 80% probability of the hail being inside the cell (for FL200 and above), and 20% of it being under the downwind side of the anvil.

I believe this flight was in cruise phase above FL200? Is this Airbus paper incorrect or am I misinterpretting it?

On page 4 of the document is shows a graphic of reflectivity and "wet hail" and "dry hail" are indicated.

"The shape of the radar echo, as well as their color, should be observed to identify storms containing hail" pg 14 pp 2

The paper also shows that even at ground level hail remains within 2nm of the edge of the parent cell.

From

"Passenger Beau Sorensen, from Provo, Utah, said: "There were times when we felt like the air dropped out from under us.

“We could see lightning spider-webbing over the wings and hail pounding the plane.”

This would also seem to suggest that the plane was inside the cell itself, no?

Flightaware shows that the crews diversion was many miles from the storm cells. However, you never know what you will run into anywhere near ( 20 nm) Level 6 super storm cells, which these were. The anvils of these cells are 40 miles high and can be 30 miles wide. Years ago, I was pelted by hail in this area resulting in some wing damage - I was at least 40 nm from the nearest storm cell.

[Jangot]

The pointy bit at the front of the A320 is called a Radome because Airbus calls it a Radome - and it covers the weather radar antenna as well as providing an aerodynamic profile for the front.

The Radome also covers the Localiser Antenna and the Glide Slope Antenna.

There is no GPS Antenna in there. On an A320, the GPS Antennae (normally 2) are mounted on the upper forward fuselage, approximately above the forward passenger door and the second one a bit aft of that.

[balderdash]

Airbus should change their documentation to 80% 19% and 1% a LOOOONNNGGG way away

FlightAware... nice app.

[bamnutsak]

BTW it has nothing to do with ATC. Diversions are purely the prerogative of the pilot in command..

Meh. In the U.S. pilots usually request a diversion, then ATC approves it, or doesn't.

I am not a pilot but have flown far too many BiS miles in the U.S. on UA (Ch. 9).

[balderdash]

The Pilot in Command (PIC) always has the last say, although he might have to justify his/her call to the FAA afterwards.

"There is no GPS Antenna in there. On an A320, the GPS Antennae (normally 2) are mounted on the upper forward fuselage, approximately above the forward passenger door and the second one a bit aft of that."

The article says "destroyed" the GPS, whatever that means. Both Antenna damaged? Inside the fuselage skin. There must be backup GPS computers as well. Hmmm.

[Jangot]

I noted that the GPS Antennae were mounted ON the fuselage skin - i.e. externally on the surface. They are a composite shell, so could have been damaged by the hail, they are certainly in a vulnerable position near the front. But they are not mounted inside the Radome.

The GPS Computers are tucked safely in the belly of the aircraft.

[balderdash]

aha, I see, thxs

[khaosai]

Some fairly large storms in the area at the time which would warrant a deviation off track. The deviation in a perfect world would be upwind with a lateral distance from the thunderstorm of at least 20 nautical miles.

Ice and hail are far less reflective that water thus the weather radar onboard modern aircraft does pose some limitations. On occasion in cruise flight you might need to go from the automatic tilt setting to the manual tilt setting and adjust the radar downwards to get an accurate picture of what's ahead by picking up the water content in the cloud.

The same challenge occurs when flying over sea compared to flying over land. The thunderstorms over the ocean are generally a lot less reflective than storms over the land thus a good understanding is required.

This may well have been an encounter in the actual cloud or perhaps flying below the anvil in what may look like clear air until it's too late.

One of the real threats associated with significant radome damage is that it can lead to unreliable airspeed indications.

Glad the aircraft landed safely.

[NeverSure]

It's worth reading the rest of the story in the OP link. While many comments on here are true such as hail being found some distance from a thunderstorm the OP link says this:

"...the plane flew through a powerful thunderstorm in Nebraska near the Colorado border with one passenger describing it as a “terrifying roller coaster ride”.

Federal Aviation Administration spokesman Ian McGregor said the Airbus A320 was diverted and landed safely at Denver International Airport at 8:42pm.

The plane dropped 14,000 feet in altitude over a two-minute time span."

It's apparent that the plane got into or much too close to the cell itself and these cells were being reported as very large and strong. They got right into the wind shear which is violent and very dangerous even to a plane of that size.

It's very fortunate that the plane landed safely. Not even airliners are designed to take that abuse.

Cheers.

Edited August 10, 2015 by NeverSure

[kiniyow]

Those Engine Fan blades must of taken a beating but the engines kept running..Over NY Birds took all engines out!

[tonypace02]

In the U.S. we pin the label "Hero" on soldiers thousands of miles away from a combat zone in a secure bunker playing video games with drones and civilians' lives, and snipers who shoot kids from a hundred yards away while their rooftop killing site is protected by soldiers below. I don't think applying the term HERO to these pilots is too great a reach.

[hawker9000]

Some would say that in order to encounter hail this large, a pilot is probably flying where he shouldn't be (i.e., too close to the storm). Hail only gets large when the updrafts are powerful enough to keep lifting hail bits over & over again until they finally become so large they can no longer be lifted and finally fall through. I've always understood that the lifting action occurs below and within the core of the storm, but that powerful downdrafts and large hail can occur in the clear air outside the storm, and for this reason it's not good enough to just not fly through a storm cell; one must avoid the clear air in their vicinity as well. The following link is to FAA Circular 00-24C (PDF) which does contain relevant background information and some helpful illustrations:

http://www.faa.gov/documentlibrary/media/advisory_circular/ac%2000-24c.pdf

It also specifically includes among its many safety recommendations avoiding flying under the anvil, and avoidance by a margin of 20NM "any thunderstorm identified as severe or giving an intense radar echo". It also recommends circumnavigating "the entire area if the areas has 6/10 thunderstorm coverage". I really don't know whether either of these criteria were met in this instance or not, nor do I think anyone else commenting here does either. The FAA will be doing a pretty thorough dig though, I have no doubt.

I have no idea what the preflight or inflight weather data available to the pilots did or didn't include, what the aircraft weather radar was showing, what other pilots who'd flown through the area might've experienced & reported, what the pilots could actually see out the windscreen during the lead-up to the encounter, or for certain what aircraft systems were affected other than the GPS & weather radar. So too early to either praise or condemn the pilots based just on a damaged radome and windscreen, IMO.

Edited August 10, 2015 by hawker9000

[natway09]

Well done to the flight crew, but the question should be asked of both flight control & pilot "how the hell did you get caught in this situation in the first place?"

[HooHaa]

armchair experts bickering over nothing, armed with everything but facts. how very boring you lot are.

Edited August 11, 2015 by HooHaa