Crossair Flight 3597

Investigation

While Captain Lutz was an experienced pilot, his competence soon came under close scrutiny by investigators from the Swiss Aircraft Accident Investigation Bureau (AAIB). The AAIB would conclude that the accident was a controlled flight into terrain (CFIT) caused by a series of pilot errors and navigation mistakes that led the plane off-course. This course deviation caused the plane to crash into a hilltop, 4.05 km short of and 150 m north of its assigned landing strip, runway 28.

Flight 3597 had originally been scheduled to land on runway 14, the main landing runway at Zurich, which was equipped with an ILS system that provides vertical and lateral guidance to the runway. The CVR records Lutz and Löhrer discussing "the 14 approach" as well as Lutz's request that Löhrer call out the height when the plane reached 100 feet above DA (decision altitude – the altitude at which an immediate decision to land or initiate a missed approach must be made). However, Flight 3597 was behind schedule and would not reach Zurich until after 22:00 CET, necessitating a change to its landing plan. Zurich ATC, in order to comply with a new Swiss law designed to reduce airport noise from approaching aircraft over southern Germany in the late evening hours, redirected all flights on final approach to switch from the ILS-equipped runway 14 to the less-accurate VOR/DME-equipped runway 28. This runway change forced Lutz to abandon his planned ILS approach and required Löhrer to consult the Jeppesen charts for runway 28. The charts included a new set of approach parameters, of which the higher minimum descent altitude (MDA) was the most crucial piece of information.

The MDA states the minimum altitude in MSL to safely fly above any obstructions or terrain in the final approach flight-path before visual contact with the runway is made. Unlike a DA in a precision approach, an MDA requires that after crossing the Final Approach Fix, the pilot should descend and maintain MDA until the pilot reports that the runway is in sight, allowing the landing to safely be completed visually. In contrast to the ILS approach, which displays lateral and vertical position, the VOR/DME approach only shows the lateral position of the aircraft and its range to the runway. Due to increased azimuth error associated with the use of VORs and lack of vertical guidance (glide slope), the MDA is therefore often higher than a DA (Decision Altitude) for an ILS.

Although both pilots were based in Zurich and the CVR picks up Lutz's query to Löhrer about Löhrer's familiarity with "the 28 approach", which Löhrer confirmed he had, Lutz put the plane into an overly steep descent that brought Flight 3597 to MDA far too soon. When Löhrer reported the plane reaching 100 feet above MDA, the CVR records Lutz asking Löhrer, "Do we have ground contact?" Löhrer hesitated before replying, "Yes". However, flight simulators programmed with the time of day, terrain, and weather Lutz was facing at that time allowed investigators to determine that the only ground Lutz or Löhrer could see was the ground of the hilly terrain over which the plane was flying. Upon reaching MDA of 2400 ft, Lutz declared that he had "ground contact" and would continue on, then deliberately descended the plane below the MDA without having the required visual contact with either the approach lights or the runway, a major piloting error that ultimately led to the crash. The fact that Löhrer made no attempt to prevent the continuation of the flight below the MDA also contributed to the crash. Lutz made an additional error by not monitoring the DME as he made his approach; the CVR recorded Lutz's running narrative on nearly every move he made in the cockpit, but did not record any readout of the DME after a check, verified by Löhrer, at 11 km from runway 28. Moments before the crash, Lutz's running commentary indicated to investigators that he thought he was at or near 4.1 km from runway 28 because he said, "Someone said he saw the runway late here". Instead, Lutz was over 7.4 km from the runway, and could not possibly have seen the runway due to the presence of a hill below the MDA of 730 m, which obscured his view. Just before the crash, the synthetic voice of the ground proximity warning system (GPWS) announced the radio altimeter reading 150 meters above ground. Lutz exclaimed, "Shit, two miles he said, he sees the runway!" A few seconds later Lutz said, "Two thousand" and then one second later the synthetic voice gave the "minimums" GPWS message, which was triggered by the radio altimeter reading at 90m. Even though Lutz finally realized that his inability to see the runway meant he needed to initiate a missed approach maneuver (called a "go-around"), his call for the go-around came too late; the plane's engines were not able to spool up fast enough to generate sufficient thrust to climb above the hill that had been obstructing his view, and the plane crashed into the hilltop at 22:06 CET.

Final report

The AAIB report determined that Lutz had failed to perform correct navigation and landing procedures on previous occasions, but no action had been taken by Crossair to remove him from transporting passengers. Lutz had twice failed to upgrade his flight certifications to the more complex MD-83 due to insufficient comprehension of its computerized navigational systems. The report also documented Lutz's role in causing the total loss of a Crossair Saab 340 by retracting its landing gear while it was still on the apron, which led to Crossair relieving him of his flight instructing duties in 1991.

In spite of those demonstrated deficiencies, however, Crossair continued to allow Lutz to fly passengers (reportedly due to a shortage of qualified pilots), and he continued to demonstrate his overall deficiencies as a line pilot. These included a near-miss incident on final approach to Lugano Airport where Lutz came within 91 m of colliding with the shore of Lake Lugano during a dangerous 1200 m-per-minute descent and a navigational error during a sightseeing tour over the Alps that took the flight far off its course to Sion. In this particular incident, Lutz missed his approach into Sion and circled over what he thought was Sion's airport for several minutes before passengers spotted road signs in Italian; the navigational error had taken them over the Great St Bernard Pass, and the airport they had been circling was in fact Aosta Valley Airport in Italy.

The final report of the AAIB states that other factors also contributed to the accident:

The range of hills the plane crashed into was not marked in the Jeppesen approach chart used by the crew.

Despite the hilly terrain surrounding it, the approach to runway 28 was not equipped with a Minimum Safe Altitude Warning (MSAW) system, which triggers an alarm if a minimum safe altitude is violated.

Zurich Airport's means of determining visibility were inadequate for runway 28.

The visual minimums at the time of the accident were actually inappropriate for using the standard approach to runway 28.

An inexperienced air traffic controller was alone in the control tower. A more experienced controller might have allowed the flight to land on runway 14 because of the poor weather conditions.