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Austrian A320 hail encounter near VIE

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Austrian A320 hail encounter near VIE

Old 11th Jun 2024, 07:46
  #21 (permalink)  
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Looking at the damage I am more surprised that the pitot tubes are even still attached to the aircraft...

The radome, radar and windows are easy enough to fix, but damage to the engines and leading edges is probably a different matter...


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Old 11th Jun 2024, 09:44
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Originally Posted by Xray4277
...............surely this was just a case of making a Cat3 ILS approach and let the Airbus do what it's good at. Not that your average passenger would know about that, but it's really just a 'nothing to see here' story - well apart from the busted nose LOL
Well, try landing a CAT lllB with those windshields !! Very very tricky and awkward.

And I think the LOC antennas are located in the nose cone forward of the bulkhead ? , so potentially those would have been broken by the hail.
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Old 11th Jun 2024, 10:59
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Originally Posted by Jhieminga
I guess the pitot probes are a bit further back on an A320 than they are on a VC10 (see my post #3 above). It would be too much to hope for to have a Hunter flying alongside in this situation too.

I wonder what the autopilot can do to circumvent an unreliable airspeed situation. It looks like the static ports are pretty close to the radome, but they are not as susceptible to disturbed airflow as the pitots will be.
Once air gets turbulent, it won't get that smooth soon, be it 50 cm or 3 m aft of the (hefty) turbulence creator. In those circumstances, the aircraft flies at roughly 70 m/s and the air "doesn't move", so in the less than 0.05 seconds, the turbulent air doesn't smooth out.
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Old 11th Jun 2024, 11:17
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On the 320, a destroyed radome does not immediately call for the application of the "Unreliable Airspeed" checklist. Seeing that all 3 pitot tubes are about at the same distance from the nose, it would be rather hard to fault one of the 3 probes as with a complete destruction of the radome, they all get fed the same turbulent air and may well come up with an equal error. If none of the 3 speed indicators end up showing wildly different figures from the other(s) and neither does the aircraft feel strange with regards to pitch vs. power, speed and vertical speed, IŽd not really consider requiring that checklist to be read. Initially.

However, the checklist holds two or three interesting points. Firstly, it shows pitch/power values versus altitude and a speed that can be expected, consequently, it can be used to check the IAS indications plausibility even if all 3 are suffering from the same error. Secondly, it provides information on the effects of a radome distruction, namely the need for an increased N1 and also a higher fuel flow that may be of interest should one find oneself far from an usable airfield when the situation arises.

I dare say that in Airbus logic, if a destroyed radome is not formally linked to any checklist, it may well be assumed that its effect on the pressure probes is negligible.
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Old 11th Jun 2024, 11:59
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If proven that the copilot was on his own in the flight deck it would be interesting to know more about their experience level. I have witnessed in the past hesitation to do a couple of degrees turn for literary a mile or two to avoid flying right through a CB, simply because the ATC frequency was to busy.

Last edited by eagle21; 11th Jun 2024 at 12:16.
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Old 11th Jun 2024, 12:42
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Originally Posted by Loose rivets
I'd be interested to know if that's a waveguide, or if the interpretation of the returns is done before being sent through the bulkhead.
The following document gives a good overview of all components and how they are hooked together.
https://aea.net/avionicsnews/anarchi...borneradar.pdf

Originally Posted by langleybaston
Query from a well-retired meteorologist: is the wavelength of aircraft weather radar fixed, and indeed fixed to detect objects from cloud droplet to rain drop size?
If so, a centimetric length might help detect mature hail.
Am I re-inventing the wheel, or asking the impossible please?
The magnetron, the wave guide and the antenna are optimised for a fixed frequency.
If the HF amplifier provides a signal that significantly departs from that design frequency, the standing wave ratio (SWR) will be horrible and much of the wave energy will be reflected into the amplifier and will kill it.

As I understand it, most of modern airborne weather radars use the X-band on the frequency 9.375 GHz, with some of them using the alternate frequency 9.345 GHz.
This is a wave length of 3.2 cm, thus a quarter wave of 0.8 cm (optimal reflection for drops of that size).
Older weather radars are using the C-band in the range 5.350 - 5.470 GHz (wave length 5.48 - 5.61 cm).
The sensitivity in X-Band is higher than in C-Band but the C-Band is thus less impacted by attenuation and has a longer range.
There are discussions for opening new airborne weather radar frequencies in the range 15.4 - 15.7 GHz (wave length 1.91 - 1.95 cm).
It would have an optimal sensitivity on 0.5 mm drops at the expense of event more attenuation at long ranges.

Hail IS detected by weather radars but the problem is that its reflectivity is much lower than the reflectivity of liquid droplets.
Thus the return of an area with a heavy hail density is depicted similarly to an area with a much much lower density of liquid droplets.
I understand that the 2 currently successful strategies for detecting the areas containing hail are:
- Measuring the reflectivity differences between 2 waves with perpendicular polarisations. Hail is usually oblong or with irregular shapes while droplets are close to be spherical.
Thus the variance of reflectivity between the 2 polarised waves will be bigger for hail than for liquid droplets.
- Measuring the reflectivity differences between 2 waves using largely separated frequencies chosen so that small liquid droplets will reflect both waves with Raleigh scatterring while the bigger hailstones will reflect the highest frequency with Mye scattering..
Mye scattering is more powerful (has a larger cross section) than Raleigh and dominates when the particle size is larger than a tenth of the wave length.
Thus this strategy is based on detecting the difference in size between hailstones and droplets and, again, identifies hail through a larger differential between the 2 waves returns.

Last edited by Luc Lion; 11th Jun 2024 at 13:34.
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Old 11th Jun 2024, 17:34
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With regard to anything appearing in the ex radar. Didn't show on BA9 did it ... Regardless well done crew with ' startle ' factor
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Old 11th Jun 2024, 18:19
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Originally Posted by Luc Lion
The following document gives a good overview of all components and how they are hooked together.
https://aea.net/avionicsnews/anarchi...borneradar.pdf


The magnetron, the wave guide and the antenna are optimised for a fixed frequency.
If the HF amplifier provides a signal that significantly departs from that design frequency, the standing wave ratio (SWR) will be horrible and much of the wave energy will be reflected into the amplifier and will kill it.

As I understand it, most of modern airborne weather radars use the X-band on the frequency 9.375 GHz, with some of them using the alternate frequency 9.345 GHz.
This is a wave length of 3.2 cm, thus a quarter wave of 0.8 cm (optimal reflection for drops of that size).
Older weather radars are using the C-band in the range 5.350 - 5.470 GHz (wave length 5.48 - 5.61 cm).
The sensitivity in X-Band is higher than in C-Band but the C-Band is thus less impacted by attenuation and has a longer range.
There are discussions for opening new airborne weather radar frequencies in the range 15.4 - 15.7 GHz (wave length 1.91 - 1.95 cm).
It would have an optimal sensitivity on 0.5 mm drops at the expense of event more attenuation at long ranges.

Hail IS detected by weather radars but the problem is that its reflectivity is much lower than the reflectivity of liquid droplets.
Thus the return of an area with a heavy hail density is depicted similarly to an area with a much much lower density of liquid droplets.
I understand that the 2 currently successful strategies for detecting the areas containing hail are:
- Measuring the reflectivity differences between 2 waves with perpendicular polarisations. Hail is usually oblong or with irregular shapes while droplets are close to be spherical.
Thus the variance of reflectivity between the 2 polarised waves will be bigger for hail than for liquid droplets.
- Measuring the reflectivity differences between 2 waves using largely separated frequencies chosen so that small liquid droplets will reflect both waves with Raleigh scatterring while the bigger hailstones will reflect the highest frequency with Mye scattering..
Mye scattering is more powerful (has a larger cross section) than Raleigh and dominates when the particle size is larger than a tenth of the wave length.
Thus this strategy is based on detecting the difference in size between hailstones and droplets and, again, identifies hail through a larger differential between the 2 waves returns.
Thank you very much indeed. I understood most of that! My take is that range is not / should not be the top priority
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Old 11th Jun 2024, 18:54
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Originally Posted by happyjack
I once flew for a company that insisted that "pilot related" damage to the aircraft had to be paid for by the pilot! That could spoil your retirement plans?
I have flown for places with an "accident fund" that we all paid into and got as a bonus at year-end if we didn't spend it on anything, but I don't think you can legally make your employees pay for wrecked airplanes.
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Old 11th Jun 2024, 19:53
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Originally Posted by langleybaston
Query from a well-retired meteorologist: is the wavelength of aircraft weather radar fixed, and indeed fixed to detect objects from cloud droplet to rain drop size?
If so, a centimetric length might help detect mature hail.
Am I re-inventing the wheel, or asking the impossible please?
I recall many years ago that a 3mm wavelength was sent out by a generic basic wx radar but this 25 years old information & ATPL theory so I may be or as the wife always says, very , very wrong
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Old 11th Jun 2024, 19:55
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The BBC have the story now. This is one paragraph from their report:
In a statement to the BBC, Austrian Airlines said the incident occurred after the aircraft flew into a thunderstorm "which was not visible on the weather radar", adding that no passengers were injured in the saga.
https://www.bbc.co.uk/news/articles/c8771lyjmveo
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Old 11th Jun 2024, 20:55
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TBH all one can sensibly do is avoid a painted cell to the upwind side, but in fairness to the crew, the weather that came through this part of Germany heading towards Vienna, was very wild and violent,
I was glad not to be flying on a night like this.
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Old 11th Jun 2024, 21:20
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My Dad flew a Wellington into a hailstorm in WW2 which resulted in some very large holes in the airframe. Thankfully due to Mr Barnes Wallace geodetic design, there was a lot of redundancy in its airframe and I am here to tell the story
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Old 11th Jun 2024, 22:47
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Thanks, Luc Lion, things have come a long way since my days nights of plodding to Spain with no radar. When finally British Eagle was ordered to fit radar on their Viscounts, they went to Cambridge to have pressure bulkhead installed. Sadly, they'd sold the jigs to Marshalls of Cambridge a while before and each aircraft now cost what the jigs had fetched.

Your link Page 81.
This waveguide pressuriza-tion prevents arcing of the RF
This surprised me.

There were advantages to flying the DAK. I recall hauling my head back into the cockpit and bellowing FULL FLAP! and then sticking it back into the gale.
However, I doubt there'll ever be another Jimmy Edwards who landed with his feet with his body half out of the roof hatch. IIRC, this earned him the DFC.

Last edited by Loose rivets; 11th Jun 2024 at 22:57.
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Old 12th Jun 2024, 03:39
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"However, I doubt they'll ever be another Jimmy Edwards who landed with his feet with his body half out of the roof hatch. IIRC, this earned him the DFC".
That reminded me of the Tony Hancock sketch series 4, 'Test Pilot', had to listen to it again!
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Old 12th Jun 2024, 06:39
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One hears that autoland was not used (available?) and unreliable airspeed was an issue.
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Old 12th Jun 2024, 14:02
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Originally Posted by WideScreen
Once air gets turbulent, it won't get that smooth soon, be it 50 cm or 3 m aft of the (hefty) turbulence creator. In those circumstances, the aircraft flies at roughly 70 m/s and the air "doesn't move", so in the less than 0.05 seconds, the turbulent air doesn't smooth out.
I fully agree with that. No doubt the pitots still had turbulent air to work with. I did not have a chance to look up where they are on the A320 family. For a static port, having turbulent air flowing past it will not change the static pressure all that much.
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Old 12th Jun 2024, 15:27
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Originally Posted by Jhieminga
I fully agree with that. No doubt the pitots still had turbulent air to work with. I did not have a chance to look up where they are on the A320 family. For a static port, having turbulent air flowing past it will not change the static pressure all that much.
Actually, the static ports and pitot tubes are carefully positioned to take care, the airflow does provide a proper representation of the actual parameters. Just moving these some 10-20 cm can bring a significant difference in reading. Let alone, when the airflow grossly changes due to the changed "layout" in front (or even close behind/above/below) the ports.

Drop the words "fluid mechanics streaklines" in YouTube and you'd be surprised how much the flow patterns change due to small variations in geometry. Solving the Navier-Stokes equation is a very difficult task, pretty much non-deterministic as well only somewhat possible for limited situations. For the rest, it is just experimenting with geometry/placements until you found a suitable layout to be able to get useful measurements. So, the large deviation from the normal, when the radome is shattered screws up everything in this area.

The turbulence itself may smooth out the measured values somewhat, though the smoothed out value will be (far) off, due to the "positional" errors. The turbulence itself may reflect as a kind of flutter on top of the average value and as such, the software may decide "something is wrong, not normal" -> "unreliable airspeed/altitude". For a C172, these parameters are inherently inaccurate, the human eye/brain manages to do some averaging and the whole is not that critical, so still bearable. For commercial flying, with a required accuracy of just a few knots, it is not.

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Old 12th Jun 2024, 17:16
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The pitot probes are sized to be well outside of the (normal) boundary layer effects. Even with a seriously screwed up flow from the damaged radome, I wouldn't expect a big effect on the sensed total pressure (P2) as most of the low disruption would be closer to the body than the total probe. Static, on the other hand, might see some effects as the flow detaches/re-attaches which does some really weird things to the boundary layer.
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Old 12th Jun 2024, 19:56
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Static ports are very sensitive to disturbed airflow, especially if not uniform between sides. Even a ridge of ice forward of the static port will cause significant impact, so nose cone damage of this degree would likely have an impact.
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