VLA sensitivity to wakes

Hm, that is strange. The ICAO recommended wake separations are 4 miles for a Heavy behind Heavy on approach/take-off, 5 miles for cruise – only 25 % bigger. For a Heavy behind Ai-380, it is 10 miles for approach/take-off, 15 miles for cruise – only 50 % bigger. Whereas the cruise speed, at about 0,85 Mach or 500 knots TAS, is at least 200 % greater than the speeds on approach/take-off (around 150 knots…). So a plane at a minimum safe distance behind a craft cruising ahead is leaving at most a half, and likely one-third, the time for wake decay that is allowed on approach/take-off.

How do the separation requirements change from 4 miles takeoff limit to 5 miles cruise limit over the course of the climb?

And that is reasonable, because wake intensity is not constant. It decreases with airspeed and configuration, so that the wake of a cruising aircraft is considerably lower amplitude than that of a approaching aircraft with similar weight. Same with sensitivity: At cruise speed a wake would induce lower forces than at approach or take-off speed (same vortex strength, same aircraft, same configuration). Additionally, any turbulence or even upset is far less dangerous in cruise as ground clearance is suffcient to counteract and small deviations from planned flight-path is less of concern.

AA587 was about 120 seconds behind the Japan Airlines B747. Vortex decays with time, not distance. ICAO recommandations quoted are for approach/take-off. Seperation grows for cruise, although cruise vortex encounter is far less dangerous (and therefore normally not mentioned).

Hm, that is strange. The ICAO recommended wake separations are 4 miles for a Heavy behind Heavy on approach/take-off, 5 miles for cruise – only 25 % bigger. For a Heavy behind Ai-380, it is 10 miles for approach/take-off, 15 miles for cruise – only 50 % bigger. Whereas the cruise speed, at about 0,85 Mach or 500 knots TAS, is at least 200 % greater than the speeds on approach/take-off (around 150 knots…). So a plane at a minimum safe distance behind a craft cruising ahead is leaving at most a half, and likely one-third, the time for wake decay that is allowed on approach/take-off.

How do the separation requirements change from 4 miles takeoff limit to 5 miles cruise limit over the course of the climb?

It’s always easier to blame the dead guy in order keep the living (persons/company) clear of the inevitable lawsuits. Plus, we’ve yet to see a dead pilot be able to speak on his own behalf. Instead, we have hundreds, if not thousands, of “experts” judging the actions of a few in perfect hindsight. Nothing like a board of suits spending years to judge an action that someone had only seconds to comprehend let alone react to.

Sorry, I do not know the pilot (not even his name). I just draw my conclusions from the available information. I do not judge the pilot as an individuum, I just judged him as pilot. And in this function, he certainly did a fatal mistake and, as I said, that was partly contributed by AA training and A300-600 rudder control mechanism. Those “experts” actually are experts. The pilot misjudged? Why did he do it? Read the report!

I agree with you.
This is why American Airlines are bitterly defending their pilot.
Its because of all this, I reserve judgement on who or what was responsible.

American law suit resulted in a 95%-share of “financial responsibility” for AA. Maybe all the high-paid lawyers did not get it right? Don’t you think that if there was any possibility of blaming Airbus of the accident they would have tried it. After all, I in the first place blame AA and not the individual pilot for that accident.

Exactly how many miles behind the 747-400 was the Airbus 300 when wrecked?

Please, the aircraft wasn’t wrecked by the vortex but by the pilot (or if somebody wants to believe by the faulty VTP, but definitly not the vortex). AA587 was about 120 seconds behind the Japan Airlines B747. Vortex decays with time, not distance. ICAO recommandations quoted are for approach/take-off. Seperation grows for cruise, although cruise vortex encounter is far less dangerous (and therefore normally not mentioned).

Large aircraft are still sensitive to wakes. I remember seeing a few pictures of 707’s and DC-8’s who had engines removed by the wakes of similar aircraft they were following. Sure, the dangers for a 747 are different than a C152 but there are still risks.

Isn’t only the 753 considered a Heavy aircraft? I believe I have also heard the Heavy callsign for 739’s as well but I could be mistaken. I know there was an attempt to get the 737NG’s recategorized as the wakes off their new wings packed quite a punch when compared to the previous 737’s. I know the few times I’ve gotten rocked rather hard by a previous airplanes wake it was reported as a 738 or 739.

Well, somehow the ordinary Heavies are thought to be less sensitive. Light aircraft are allowed to get 6 miles behind a Heavy, Medium aircraft are allowed to get closer inside the wake, to 5 miles, and Heavies are allowed to get to 4 miles behind another Heavy.

Can it be proven by testing that all Heavies whether a 767-200 or 747-400 are safe to fly less than 5 miles behind another Heavy, like a 747-400?

Exactly how many miles behind the 747-400 was the Airbus 300 when wrecked?

Can it be argued that the VLA might be safe less than 4 miles behind a Heavy, the way it sounds accepted that Heavies are safe at less than 5-6 miles behind a Heavy?

I see.

I wasn’t being touchy, genuinely had no idea what you were on about

Touchy!!!!

Look at my spelling in posting #19….. :D:D:D

what’s that supposed to mean?

At least you can spell “investigative”…….. 😮

The NTSB is the responsible US authority and their findings on this terrible incident are available for all to see.

I presume that we can agree that their invesigations will have been far more thorough and authoritative than any of our speculations.

Yes indeed we can.

However, the belief is still there that the blame cannot be shifted squarely on the pilots shoulders as Schorsch seems to beleive. We’re airing different points of view on that, not disputing official investigative results.

The NTSB is the responsible US authority and their findings on this terrible incident are available for all to see.

I presume that we can agree that their invesigations will have been far more thorough and authoritative than any of our speculations.

It’s always easier to blame the dead guy in order keep the living (persons/company) clear of the inevitable lawsuits. Plus, we’ve yet to see a dead pilot be able to speak on his own behalf. Instead, we have hundreds, if not thousands, of “experts” judging the actions of a few in perfect hindsight. Nothing like a board of suits spending years to judge an action that someone had only seconds to comprehend let alone react to.

I agree with you.
This is why American Airlines are bitterly defending their pilot.

Its because of all this, I reserve judgement on who or what was responsible.

Hence we can clearly conclude who is responsible.

It’s always easier to blame the dead guy in order keep the living (persons/company) clear of the inevitable lawsuits. Plus, we’ve yet to see a dead pilot be able to speak on his own behalf. Instead, we have hundreds, if not thousands, of “experts” judging the actions of a few in perfect hindsight. Nothing like a board of suits spending years to judge an action that someone had only seconds to comprehend let alone react to.

Airbus say the pilot acted wildly, American say he did what he was trained to do.

So there is no way you or I can sayfor sure who is to blame. Personaly I say both parties have responsibility. Although to Airbus’ credit, the tail didn’t snap till around 130% designed max load.

I would orientate myself on the official report of the NTSB that clearly states that
– the co-pilot was responsibly due to “excessive and unnecessary” rudder inputs
– the training of AA contributed to the accident
– the rudder control system contributed to the accident

The tail withstood 1.9 times the limit load, that is the maximum allowed load on vertical tail. The structure behaved exactly as Airbus predicted and NTSB stated that in the report. The rudder travel limiter was object heavy criticism by authorities and the reason why AA blamed Airbus as responsible. However, the limiter is not well designed and tricky to handle, but was certified.

Hence we can clearly conclude who is responsible.

While in this case the vortex did not cause anything like strutural damage or aircraft upset. It just triggered the wild behaviour of the co-pilot.

Airbus say the pilot acted wildly, American say he did what he was trained to do.

So there is no way you or I can sayfor sure who is to blame. Personaly I say both parties have responsibility. Although to Airbus’ credit, the tail didn’t snap till around 130% designed max load.

As Airbus and American Airlines are painfully aware of! (although that was more the tail fin)

While in this case the vortex did not cause anything like strutural damage or aircraft upset. It just triggered the wild behaviour of the co-pilot.

I actually concentrated more on the aircraft as rigid-body system. But you are right: A high-energy vortex may cause structural damage at large aircraft. Especially parts like vertical tail plane.

As Airbus and American Airlines are painfully aware of! (although that was more the tail fin)

Large aircraft are still sensitive to wakes. I remember seeing a few pictures of 707’s and DC-8’s who had engines removed by the wakes of similar aircraft they were following. Sure, the dangers for a 747 are different than a C152 but there are still risks.

Isn’t only the 753 considered a Heavy aircraft? I believe I have also heard the Heavy callsign for 739’s as well but I could be mistaken. I know there was an attempt to get the 737NG’s recategorized as the wakes off their new wings packed quite a punch when compared to the previous 737’s. I know the few times I’ve gotten rocked rather hard by a previous airplanes wake it was reported as a 738 or 739.

I actually concentrated more on the aircraft as rigid-body system. But you are right: A high-energy vortex may cause structural damage at large aircraft. Especially parts like vertical tail plane.

Large aircraft are still sensitive to wakes. I remember seeing a few pictures of 707’s and DC-8’s who had engines removed by the wakes of similar aircraft they were following. Sure, the dangers for a 747 are different than a C152 but there are still risks.

Isn’t only the 753 considered a Heavy aircraft? I believe I have also heard the Heavy callsign for 739’s as well but I could be mistaken. I know there was an attempt to get the 737NG’s recategorized as the wakes off their new wings packed quite a punch when compared to the previous 737’s. I know the few times I’ve gotten rocked rather hard by a previous airplanes wake it was reported as a 738 or 739.

Knowing ICAO reasonably well I doubt they have done anything on A380 testing that quickly …

Hmm, according to my friend ad CX, the controllers at WSSS are taking up ICAO’s recommendations on the A380 seperation.

Also, he says the ICAO recommendations came from measurements and tests. What measurements and tests could these be? Perhaps something undertaking while the A380 is currently touring.