Disaster over Lake Constance - Air Regs

A tragic and unnecessary accident and my thoughts certainly go out to everyone involved.

My question to those of you who may be active jet jockies. The rules of collision avoidance as I know them are: alter your course to the RIGHT or give way. Why would a TCAS system order a climb or decent? This does not make sense to me.

Thanks,

Current TCAS technology does not provide left or right turn guidance, only vertical guidance. In the event of an RA (resolution advisory) the pilots, are given aural guidance to either climb or descend, along with visual cues illustrated on our vertical speed indicator (VSI): red arcs are placarded at vertical speeds we must avoid, or fly away from, and green arcs are placarded at vertical speeds we should fly to. For example: a TCAS RA may command us to 'descend, descend!' while the VSI shows red arcs between -1500 fpm and + 6000fpm, and green arcs between -1500fpm and -2000fpm.

If both airplanes involved in a conflict are TCAS equipped, the TCASes will 'talk' with each other, and would command each crew to fly in opposite directions (climb/descend). Since only the Boeing was TCAS equipped, it unfortunately instructed the DHL crew to descend (the same maneuver the Tu-154 was initiating), and both planes collided during their escape.

TCAS is a great tool with immense possibilities, but it is only a tool, and it isn't infallible. Obviously we need ATC to remain vigilant, even if there are only five airplanes in the sky (which was the case over southern Germany), pilots need to remain vigilant (which isn't easy after flying for eight hours), and airplanes that operate in RVSM airspace (airspace which has only 1000ft vertical separation) all should have operating TCAS equipment.

My heart goes out to the crews, families, and friends to everyone involved in this tragedy. Hopefully we can all learn from this accident, and help prevent any such accident from happening again.

Chris Fleming ATP B767, CFIG

It appears that the Tupolev was also equipped with a TCAS.

Chris,

Thank you for the interesting information on the TCAS. As Bert pointed out, the general understanding, and what I read in the press here in Switzerland is that both aircraft were TCAS-equipped, but the question is why did both decend.

My question remain. Rules of collision avoidance; if two aircraft are approaching each other the one with the aircraft on his right gives way. If two are approaching head-on, both alter their course to the right. Is this not the case in the UIR; even though you guys fly IFR.

Regards, Roderick Nimbus 4DM (wings are not much smaller than the 767) & CFIG.

Rod,

The initial reports of the accident that I read indicated that only the B-757 was TCAS equipped, but the latest reports say both airplanes were so equipped. I stand corrected.

As a general rule when visually avoiding other aircraft, yes, if two aircraft are approaching each other the one with the aircraft on his right gives way. If two are approaching head-on, both alter their course to the right. But in IFR operations, ATC has more flexibility to maintain aircraft separation. They may turn one or more aircraft off course to avoid conflicts, or change an aircraft's altitude.

As far as TCAS is concerned: the current system only has vertical guidance capability; there is no lateral guidance provided. As technology improves, I hope that future systems will incorporate both vertical and lateral guidance, so one aircraft can be instructed to 'climb right,' and the other to 'descend left.'

Obviously with this accident (as is always the case) there were multiple failures. Among others some are: -The ATC automated radar warning system was OFF for maintenance. -Only one controller was monitoring the airspace while another took a coffee break. -There was, to some degree, a language barrier between a Swiss controller speaking to a Russian pilot in English. -A possible TCAS malfunction. -And perhaps pilot/controller fatigue.

The airspace below FL360 was probably clear of other aircraft, which would explain why the controller chose to descend the Tu-154. Unfortunately, with less than a minute remaining before the collision, the Russian crew did not hear the instructions to descend, did not understand the instructions, or did not grasp the immediate nature of the instructions. When the B-757 crew finally had an RA from their TCAS, it instructed them to descend as well. Why? I don't know. It could have been a system malfunction, or the Tu-154's TCAS didn't have RA selected, which would have prevented the TCASes from 'talking' to each other. I'm just guessing.

Chris Fleming Rolladen-Schneider LS1-f (much more fun than the 767), and CFIG

One more possible source: One of the aircraft could be sending incorrect altitude on the mode S. I know one case where a TCAS equiped B747-400 got a resolution advisory 'climb, climb' while the 'conflicting' non-TCAS equipped (Russian) aircraft was transmitting the wrong altitude on it's mode C. In this particular case the B747-400 was able to establish visual contact and saw that the actual altitude of the conflicting traffic was higher than the indication of the mode C. In fact the TCAS made him climb towards this aircraft....

Ruud Holswilder Ventus 2cT, Duo Discus T, CFIG for fun, B747-400, ATPL, TRE etc for funding the fun

As I recall, altimeters in the former USSR are metric while everywhere else in Europe would be in feet. I seem to remember that we had a card that converted the metric so that we could fly off our Altimeters. Would anyone know if the 'Russian' had metric or Feet for altimeter settings? It was confusing some four years ago when flying to Mocsow and we used the cards to convert the metric instructions in to feet. RE Gaines

Except in gliders where altimeters usually are metric in Europe. The gliders with the best intruments in my club have both a metric and a feet altimeter, so we set the metric to QFE for easy glide range calculation and the feet altimeter to QNH for easy clearing of unauthorized airspace.

You're going to have to explain that. A calculation of 100 feet per km is (as far as I can see) far easier than anything you can do with a metric altimeter, and suitably on the conservative side for many gliders a club would have e.g. Grob twins and older Std class gliders. And if you had a 'spare' altimeter and were *that* worried then you'd set it to -800 feet or something on the ground.

Bruce Hoult schrieb:

Let me try

In Europe we measure distances in metres or kilometers. Also for measuring and calculating distances by means of a navigation chart we use rulers with millimeters and centimeters scaling. Of course everybody here ist used to the metric system and is more or less able to estimate distances. (Remeber what they did with the metric instruments in the Space Shuttles and why?)

If I am 2000 metres above the starting point and my glider has an L/D of 30, I can instantly calculate the farest point reachable in optimal conditions: 2km * 30 = 60km. I can now tell by estimation or by looking at the chart if I can make it home or have to look for another updraft.

HTH

The rule, as recommended by the official french teaching method, is : beginners in local flight should remain in gliding range with glide ratio 10:1, more experienced and cross country rated pilots use the same up to 500m height, then glide ratio 20:1 + 250m safety margin up to 1000m height, then real glide ratio of the glider plus appropriate margin. These values are not absolute things, the idea is merely to divide the vertical space in 3 layers where you use different glide ratio as guidelines. So using the same unit for vertical and horizontal distances make easy to compute your actual glide slope for a given target and to compare it with the above reference values.

100 feet per km is nearly 33:1, which is very close to the real 35:1 of the ASK21 or 34:1 for the ASK23 which are the typical gliders used by beginners in my club, so the conservative side in this case is almost nothing. Anyway such a 'wired in' rule doesn't allow to easily change the glide ratio you are using. French pilots often compare their gliding slope to typical values like 10, 20, 25, 30 or 40 for which the calculation is easy, provided you use the same unit in both directions.

Of course the setting to QFE is only used in flat land, in mountains QNH is the rule, and then we need a little more calculation.