1948 KLM Constellation air disaster

The KLM Lockheed Constellation airplane "Nijmegen" (identification PH-TEN) crashed near Prestwick, Scotland, on 20 October 1948, killing all 40 aboard.

Background

The aircraft was piloted by K.D. Parmentier, widely regarded as one of the great flyers of the era, and KLM's chief pilot.

"Nijmegen" was scheduled to fly from Schiphol Airport near Amsterdam at 8:00 p.m. CET, to New York via Prestwick, with Shannon International Airport in Ireland as the alternative stopover point in case of bad weather at Prestwick. The plane was delayed however as additional cargo was loaded for transport to Iceland, where there would now be an additional stop en route from Prestwick to New York.

The plane eventually left Schiphol at 9:10 p.m., crossing the English coast at Flamborough Head and then flying towards Carlisle before turning and starting to fly up the coast towards Prestwick.

The weather forecast Parmentier had been given by the Royal Dutch Meteorological Institute at Schiphol had told him that there was some slight cloud at Prestwick, but that it would likely dissipate by the time the "Nijmegen" arrived. This was incorrect however: the weather at Prestwick was steadily deteriorating.

Parmentier believed that there was a strong crosswind, blowing at right-angles to the main runway (Runway 32) at Prestwick of about 20 knots, which might prevent a landing on it. Prestwick had a second, alternative, runway (Runway 26) which was heading into the wind but had no radar-approach system. KLM pilot guidelines, drafted by Parmentier himself, forbade a landing at Prestwick in low cloud on the alternative runway.

By the time of approach, Prestwick was under drizzle and a cloud-base that was almost solid at 600 feet (180 m), forecast to continue from about 11:00 p.m. onwards, right around the time the "Nijmegen" was approaching the airfield. As the flight had taken off late, they had not picked up the radio message broadcast by Prestwick airfield informing them of this.

Parmentier was thus unaware of the deterioration in the weather: were he aware of it he would have been able to divert to Shannon. The routine weather reports broadcast from Prestwick had given a cloud cover of 700 feet (210 m). No new forecasts, which would have told Parmentier of the expected decreased cloud cover were broadcast. Nor did he know that two airliners from SAS had already turned back rather than attempt a landing at Prestwick.

Inland of the runway was high ground of over 400 feet (120 m), but the KLM-issued charts which the crew were using did not mark any land higher than 200 feet (60 m). Three miles (5 km) to the north-east of the runway, rising to over 600 feet (180 m), were a set of wireless masts. Three miles (5 km) inland ran a series of electricity pylons and high-tension cables, the main national grid line for South Scotland, carrying 132,000 volts. However the error-riddled charts gave the height of the cables at only 45 feet (14 m).

The plane made radio contact with approach control at Prestwick shortly before 11:00 p.m. At this point the cross-wind over the main runway had, unknown to Parmentier, dropped to 14 knots which made it within limits to attempt a landing on the main runway. Instead, he decided to attempt an overshoot of the main runway, followed by a left-hand turn that would bring the plane downwind of the alternate runway. He would then overfly the runway before looping round for his final approach. While it might sound complicated, Parmentier expected to be in visual contact with the ground which would make such an attempt relatively easy.

At 11:16 p.m. Prestwick broadcast a morse message warning of the deteriorating weather, however as the "Nijmegen" had now switched over to voice contact the message was not received. On the approach they were told of the decreased cross-wind and decided to attempt a landing on the main runway after all. However, three miles out Parmentier decided that the wind was probably too strong for landing on the main runway and decided to overshoot and land on the alternate. He overflew Runway 26, the lights of which he could now see, climbed to a height of 450 feet (140 m) and extended the landing gear ready for landing. At this point they ran into what Parmentier believed was an isolated patch of cloud. However this was the actual cloud-base, which was now as low as 300 feet (90 m) in some areas. At this point the "Nijmegen" was headed directly for the power cables at 450 feet (140 m), which the crew believed to be substantially lower.

Parmentier realised the 'isolated fog' he had run into was getting denser, but due to his belief that they would have visual contact with the ground the crew had not attempted to time their flight downwind of the runway. Before he could abort the attempt, the plane crashed into the electricity cables, hitting the main phase conductor line. The crew attempted to turn the now burning aircraft towards the runway with the intent of an emergency landing. However, the faulty charts led them to crash into high ground five miles east-north-east of the airfield.

All 30 passengers (22 Dutch, 6 German, 1 British and 1 Irish) and the 10 crew died. Rescue services did not reach the crash-site for over one and a half hours due to confusion over which service was responsible for responding to the crash. By the time they arrived only six people were still alive, and all died within 24 hours. Among the passengers was Prince Alfred of Hohenlohe-Waldenburg, a minor German noble.

Aftermath

The subsequent court of enquiry blamed several factors for the crash:
# The failure of the ground authorities to inform the "Nijmegen" of the deterioration in the weather.
# The failure of the crew to time their flight downwind of the runway.
# The errors in the official KLM approach chart the crew had relied on. It emerged these charts had been copied from war-era United States Air Force charts, which upon subsequent examination were also found to be faulty. The court of enquiry was astonished to find that KLM had relied on maps from a foreign authority when detailed and correct maps were available from the Ordnance Survey.

Probable Cause

The following Probable Cause was determined:quotation
#That when the pilot started his landing manoeuvre for runway 26 of Prestwick Airport the weather conditions were already below the limits for this manoeuvre but that from the weather forecasts received this could not be known to him and that this could not be personally judged at the time.
#That, although the landing on runway 26 under the weather conditions, as far as these were known to the pilot, required the greatest caution, the pilot could not be blamed for having commenced that landing procedure.
#That flying too long on the downwind-leg of runway 26 caused the accident.
#That, if no unknown circumstances contributed to the extension of the flight on the downwind-leg of runway 26, the extension was due to the delayed action of the pilot after he lost visual approach.
#That it was not impossible that a stronger wind that the pilot accounted for contributed to the extension of the flight on the downwind-leg of runway 26.
#That the possibility of other circumstances as mentioned under 4 could not be ruled out, but that no data was available which could give cause for the supposition that they contributed to the extension of the flight at a low altitude on the downwind-leg of runway 26.

References

*Ralph Barker (1967) "Great Mysteries of the Air".
* [http://aviation-safety.net/database/record.php?id=19481020-0 ASN accident record]