Controlled Flight into Terrain

Crossair Flight 3597 was an AVRO 146-RJ100, a regional airliner manufactured in the UK by British Aerospace. This aircraft type is popular at small, city-based airports because it is very quiet.

Flight 3597 was a scheduled flight from Berlin-Tegel in Germany to Zurich in Switzerland. On the 24th of November in 2001, 28 passengers, 3 flight attendants and 2 flight crew were on board. The passengers included a German family with two small children, pop singer Melanie Thornton and three members of the band Passion Fruit with their manager.

23 November

05:00 The commander of Flight CRX 3597 starts his flying day at the Horizon Swiss Flight Academy, meeting a student pilot at Zurich for a training flight. After the training flight, he flies four scheduled flights for Crossair, round trips to Tirana and Milan-Malpensa.

11:50 The first officer of Flight CRX 3597 makes four scheduled flights for Crossair: round trips to Budapest and Dusseldorf.

20:31 The commander leaves Zurich airfield after a total duty time of 15 hours and 31 minutes.

22:05 The first officer leaves Zurich after a flight duty time of 10 hours and 15 minutes. He comments to his spouse that the working day had been very stressful and that he felt exhausted.

24 November

07:30 The commander starts his flying day at the flying school. The IFR training flights finish at 13:30.

16:20 The first officer starts his flying day at 16:20.

17:20 Crossair Flight scheduled departure for Berlin-Tegel is delayed. The flight eventually departs at 17:54 and arrives at Berlin-Tegel at 19:25.

20:01 Flight CRX 3597 departs Berlin-Tegel airport on time for its scheduled flight to Zurich. The commander is the Pilot Flying (PF) and the first officer is in a support role: monitoring and handling radio communications. The flight towards Zurich is uneventful.

20:40 Aircraft is cleared to descend to flight level 240. The commander gives the approach briefing, expecting an instrument approach on the ILS to runway 14.

20:43:44 The first officer draws the commander’s attention to their speed, which was “going into the red.” The commander reduces speed and leaves the first officer to handle the navigation set up.

Commander: “Denn, äh, s’NAV setting isch up to you. Final NAV setting wär zwei Mal d’ILS” Then, er, the NAV setting is up to you. Final NAV setting should be twice the ILS.

The pilots are speaking English for all radio work and Swiss-German interspersed with English aviation phrases to each other. There’s no evidence that there was ever any comprehension issues although the transcript makes for interesting (by which I mean somewhat bizarre) reading.

20:47:56 The crew change frequency to Zurich Arrival East Sector and report that they’ve received the recorded airport information referenced as KILO. The recorded information confirms the Captain’s prediction of an instrument approach to runway 14.

The controller doesn’t mention that the recorded information has updated from KILO to LIMA to MIKE, which means that the the flight crew are working from old information. The controller does inform the flight crew that, contrary to the recorded message, they should expect a standard VOR/DME approach for runway 28.

The flight crew were expecting a precision approach to Runway 14 which involves following a pre-defined glideslope defined by the radio-navigation signals of the Instrument Landing System (ILS).

Runway 28 doesn’t have an ILS so now they have to plan a new and more complicated approach.

Commander: “Oh sh**, that as well? Fine, OK.”

20:50:00 The recorded airport information receives an update to NOVEMBER, as the cloud ceiling has dropped to 5-7/8 (broken clouds) at 1,500 feet above the airfield. The controller does not communicate this change to Flight CRX 3597. The flight crew have no reason to realise that their weather information is out of date.

20:51:56 The commander gives a new approach briefing for the standard VOR/DME approach for runway 28.

A VOR/DME approach is a non-precision approach. Rather than simply following a glide slope, you need to track a specific radial towards or away from a VOR station. After you pass the final approach fix, you reduce your altitude at specific intervals (called step downs) which are defined for each runway approach. As you approach the airfield, you should have the runway (and surrounding terrain) in sight and be able to finish your approach visually.

As you descend, the VOR gives you positional guidance, that is, you are tracking your position laterally using the VOR. The DME tells you your distance from the runway.

The “step downs” are staggered descents based on your DME distance, ensuring that you remain at a safe altitude as you approach the runway.

As you calibrate your height to your distance, you continue your descent to the minimum decision altitude for the non-precision approach. Once you reach this altitude, you must stop your descent unless you have the runway in sight and can continue the landing visually. You can continue your approach at (but not below) the minimum decision altitude until you reach the missed approach point, which is a specific distance, by DME, from the runway. If you cannot see the runway once you have reached the missed approach point, you must break off the approach and climb away.

At Zurich, Runways 14 and 16 are equipped with a minimum safe altitude warning system (MSAW). This triggers a visual and acoustic warning in the control tower if the pre-defined minimum altitudes are infringed. Runway 28 is not equipped with this safety system.

20:58:50 Zurich Arrival clears Flight CRX 3597 for the VOR/DME approach to runway 28 and instructs the crew to reduce speed to 180 knots.

21:03:01 Zurich Arrival hands over the flight to Zurich Aerodome Control 1, Zurich Tower.

There should be four working positions at the control tower at this time, however, the supervisor reduced the crew to two and then left the tower. As the approach for Runway 28 is a VOR/DME approach done under the aircraft’s own navigation, no radar vectors are given by ATC.

The aircraft is descending through 5,000 feet above mean sea level and turning right to fly onto the final approach track of 275°. They are approximately 11 nautical miles east of Zurich. During the right turn, the commander mentions to the first officer that he has visual ground contact. The minimum descent altitude is 2,400 feet.

21:03:29 The flight ahead of them is the first to execute the changed approach that evening into runway 28. They inform the control tower that the weather is uncomfortably close to the minimums. This means that they were not visual with the runway until the very last minute.

This is important information for the remaining traffic, who need to be aware that visibility is poor and they may not be able to land under the current circumstances. The current visibility doesn’t correspond with the recorded airport information and quite frankly, does not appear to good enough for non-precision approaches into runway 28.

Flight CRX 3597 is the next in line for landing.

21:04:36 They descend to 4,000 feet above mean sea level. The aircraft is travelling at 160 knots with a descent rate of 1,000 feet per minute, which later increased to 1,200 feet per minute. This is not in line with the step downs: the flight is deviating from the approach path it should be taking.

This rate of descent continued until just before the collision.

21:05:21 Flight CRX 3597 reports to ADC Tower 1 as established.

The flight crew complete the final checks.

The air traffic controller stated that he noticed on radar that the plane was at approximately 3,600 feet when the aircraft was still six nautical miles out. That is to say, it is too low for the DME distance and not following the step-downs. It is not “established”. As the aircraft is under its own navigation, the controller doesn’t keep an eye on the aircraft’s altitude.

21:05:55 The commander claims that he has visual ground contact.

At that altitude, in that visibility, it is not possible that the commander could see the airfield. He only has sporadic contact with the hilly terrain that they were directly over. His statement is, at best, overly optimistic.

It is the first officer’s role to call when the approach lights or runway are clearly in sight. Nothing is in sight. The first officer should have argued but simply said, “Yes.”

They continued the descent.

Commander: Someone said he saw the runway late here …approaching minimum descent altitude…here we’ve got some ground contact.

21:06:10 The aircraft passes straight through the minimum descent altitude at 2,400 feet.

Commander: -..two four (2,400), the minimum. I have ground contact. We’re continuing at the moment. It appears, we have ground contact, we’re continuing on.”

The first officer quietly says “Two four” under his breath.

What exactly could they see?

These images were created with a simulator as a part of the investigation, looking at similar conditions to the incoming flight.

Runway 28 as seen from the VDP at 2,390 feet with a visibility of more than 10km
Runway 28 as above with a visibility of 5km

On that cloudy night, the flight crew are flying in visibility of around 2km. The approach lights at this distance can be detected at the earliest at 2.3 nautical miles. The flight coming in previous stated that they became visual at 2.2 nautical miles.

If Flight CRX 3597 were to attempt a final approach from the minimum descent altitude at this distance, they would need to descend at an angle of 6° towards the runway threshold, too steep for a stabilised approach.

At the point at which Flight CRX 3597 descends below minimum descent altitude, the aircraft is much further from the threshold than it should be for the glide slope: they are still 4.8 nautical miles away. There’s no way they can see anything. The commander can’t possibly have visual contact to the approach lights and the runway.

To be fair, it’s a two-person crew. It is the job of the Pilot Not Flying, the first officer, to monitor the approach and act as look out. He’s expected to call attention to deviations from procedure and watch both for the decision height and the minimum descent altitude. It is his job to call when the approach lights or runway is clearly in sight.

The first officer, in his supporting role as Pilot Not Flying, says nothing.

21:06:22 The Ground Proximity Warning System (GPWS) announces the radio altimeter reading 500 feet above ground. The flat land here is at 1,500 feet above sea level, with hills rising to 2,000 feet. The aircraft is below the minimum descent altitude and still descending. The commander vents his frustration.

Commander: “Sh**, two miles, he said, he saw the runway.”

This is a reference to the previous flight inbound to Zurich who stated that the weather for runway 28 was “pretty minimum” and that they had the runway in sight at about 2.2 nautical miles away.

Flight CRX3597 isn’t two miles out, though. The aircraft is four miles out and descending fast. The captain clearly does not have the runway in sight, despite deliberately continuing past the minimum descent altitude.

21:06:31 The commander notes that they are at 2,000 feet but appears not to be taking any note of their distance from the runway. No one is watching the DME and its likely that the commander is completely focused on looking out the window. He makes no further mention of having the runway – or anything – in sight. The main cloud base is between 2,400 and 2,700 feet. Over the hilly slope, low banks of cloud are forming between 1,800 and 2,000 feet.

21:06:32 The GPWS sounds: MINIMUMS, MIMIMUMS. They are now 300 feet above the ground. The Tower controller, without realising that they are miles away and low, clears Flight CRX 3597 to land.

First Officer: …do a go around?

At this moment, they still could have saved themselves. If the first officer had initiated a go around immediately, it might still have been possible. But instead, he asks hesitantly whether they should.

21:06:34 The commander calls for a go around and the auto-pilot is switched off, possibly as a reaction to seeing the trees in the landing lights.

The First Officer says, “Go around!” The power levers are pushed towards the take-off thrust position and the engine’s RPM increases. But it’s too late.

One second later, the Cockpit Voice Recorder records the sounds of an impact as the aircraft hit the trees.

21:06:35 The aircraft collides with treetops and bursts into flame. It travels another 50 metres before crashing into the ground. The Cockpit Voice Recorder stops recording.

A survivor who was seated in 14B described the scene: “…..suddenly a loud crashing noise could be heard and the aircraft shook violently. I immediately looked forward and saw through the open cockpit door and the cockpit windscreens that outside the aircraft a real shower of sparks was rising. Next moment there was a massive impact…”.

21:22 The first vehicles from the Zurich airport fire brigade arrive at the site. White-yellow flames burn and there are several small explosions.

Twenty-one passengers and three crew members died from their injuries at the site of the accident. Seven passengers and two cabin crew members have survived. The impact and immediate fire destroyed the cockpit, the front part of the fuselage, the central part of the fuselage and large sections of both wings.

When the BFU (the Swiss Aircraft Accident Investigation Bureau) investigated, they found a disturbing background.

There were numerous previous incidents where the commander did not follow procedure and did not use his checklists effectively. Also, they discovered that he’d struggled in the past with conversion courses to the MD-80: “it became apparently that the commander was having major problems with the MD-80’s digital guidance system.” No further performance checks or detailed examination as to the reasons for his repeated failures were undertaken.

Then, the investigation uncovered a similar incident from six years previous.

According to the statement of the copilot involved, in December 1995 the commander was carrying out an approach to Lugano airport as pilot flying, at night and under instrument flight conditions. Shortly before the Saab 340 reached the PINIK waypoint at an altitude of 7000 ft QNH, the aircraft was configured for the landing, i.e. the landing gear was lowered and a landing flap setting of 35° was selected. For the descent, the commander used the autopilot’s vertical speed mode and selected a rate of descent of 4000 ft/min.

Since rates of descent of less than 2000 ft/min are usually used for this approach, the co-pilot asked for the reason for the increased rate of descent. The commander explained that one could implement the procedure in this way. During the descent, which continued unchanged to a radar altitude of300 ft RA above the lake, the speed of the aircraft increased from 135 to more than 200 KIAS. When the aircraft changed over to horizontal flight at 300 ft RA, part of the lake shore and the mountainside could be seen. The aircraft then flew at this altitude in the direction of Lugano aerodrome until the runway finally came into view and the aircraft was able to land.

The overspeed warning and the ground proximity warning system (GPWS) had been deactivated before the descent.

The commander believed it was reasonable to descend below the minimum descent height, even at night and in instrument conditions. That successful procedure at Lugano reinforced his bad habits.

In addition, in 1999, the commander became lost during a sight-seeing trip with 30 passengers above the Savoy Alps. Eventually he realised that he’d gone past his planned flight time to Sion.

He immediately initiated a descent in the direction of an aerodrome which he had in sight. This was Aosta (I) aerodrome, which is located approximately 50 km to the south of Sion in a valley which runs along the other side of the main ridge of the Alps. No discussion on the approach took place and the most important checklist points were covered intuitively and in an undefined order. The copilot tried several times to make contact again with Sion aerodrome control, which he was unable to do because of the topographical conditions.

The commander did not react to interventions from the copilot. Several descending turns were made above Aosta aerodrome and the approach was continued without radio contact. When the aircraft was making its final approach, the passengers could see from road signs that they were in Italy. The commander then initiated a go around and flew over the St. Bernhard pass into the Rhone valley, where the landing in Sion took place.

As there was no incident, this was not reported at the time. However, there were plenty of personnel notes to indicate that there was a potential issue.

The commander was described as defensive in relation to more complex technical systems and “frequently exhibited difficulty with their operation.” A number of pilots who had flown with the commander as first officers stated that he often did not integrate the co-pilots into the operating procedures and decision-making processes.

Unfortunately, the records for the First Officer were the worst possible contrast: his personnel reports showed that although he was well-qualified and his skill level was good, four separate recruitment officers all found that he had “a tendency to subordinate himself.” He was described as lively but not aggressive and his assessments stated that he needed to develop self-confidence and personal maturity.

Earlier in the accident flight, the commander had lectured the first officer about his interpretation of the runway report, which the first officer had just deciphered “more or less completely and competently” according to the report. Thus the commander, with forty times more flying experience than the first officer, underlined his position of authority. Small wonder that the first officer didn’t dare argue.

Causes

The accident is attributable to the fact that on the final approach, in own navigation, of the standard VOR/DME approach 28 the aircraft flew controlled into a wooded range of hills (controlled flight into terrain – CFIT), because the flight crew deliberately continued the descent under instrument flight conditions below the minimum altitude for the approach without having the necessary prerequisites. The flight crew initiated the go around too late.

The investigation has determined the following causal factors in relation to the accident:

  • The commander deliberately descended below the minimum descent altitude (MDA) of the standard VOR/DME approach 28 without having the required visual contact to the approach lights or the runway
  • The copilot made no attempt to prevent the continuation of the flight below the minimum descent altitude.

As always, the cause was not quite that simple and there were a number of secondary issues flagged by the investigation which could have limited the accident to a close call rather than a fatal crash.

The following factors contributed to the accident:

  • In the approach sector of runway 28 at Zurich airport there was no system available which triggers an alarm if a minimum safe altitude is violated (minimum safe altitude warning – MSAW).
  • Over a long period of time, the responsible persons of the airline did not make correct assessments of the commander’s flying performance. Where weaknesses were perceptible, they did not take appropriate measures.
  • The commander’s ability to concentrate and take appropriate decisions as well as his ability to analyse complex processes were adversely affected by fatigue.
  • Task-sharing between the flight crew during the approach was not appropriate and did not correspond to the required procedures by the airline.
  • The range of hills which the aircraft came into contact with was not marked on the approach chart used by the flight crew.
  • The means of determining the meteorological visibility at the airport was not representative for the approach sector runway 28, because it did not correspond to the actual visibility.
  • The valid visual minimums at the time of the accident were inappropriate for a decision to use the standard VOR/DME approach 28.

The primary issue that caused this fatal accident in the end was Cockpit Management Resources. Over time, we have learned that the interaction in the cockpit is vital to the safe management of critical phases of flight. The Pilot Not Flying, often the less experienced first pilot, must be confident enough to speak up and the Pilot Flying must be willing to accept his support.

The combination was fatal: a complicated approach in minimum conditions to be executed an authoritarian commander paired with a first officer who didn’t have the strength to argue.

The decision to continue the descent into foggy ground was possibly affected by the commander’s fatigue as well as his lack of technical prowess. He appears to have hoped desperately to make visual contact rather than to reference his instruments.

Throughout the dangerous final approach, the first officer said nothing and took no recorded actions from the time when the aircraft descended past the minimum descent altitude to his final hesitant question of whether they should go around. It appears that he recognised their descent without visual references as an error and yet was not able to take action. And in the end, they — and twenty-one innocent passengers and crew — paid the price.

References

All photographs are taken directly from the accident report.


Can I tell everyone yet? YES! I can!

Wheeeee! I’ve been waiting to tell you guys about this for ages!

Ahem.

If you found this analysis interesting, please keep an eye out for my book: Why Planes Crash: 2001, due for release the first week of May.

More details soon. :)


Category: Accident Reports,

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