The affair began with a mistake made by the German aviator Major Erich Hoenmanns , the fifty-two-year-old base commander of Lodderheide airfield, near Münster. On the morning of 10 January, he had been flying a Messerschmitt BBf 108Taifun, an aircraft used for reconnaissance, liaison, and other miscellaneous roles, from Loddenheide to Cologne when he lost his way; extensive low fogbanks obscured his view of the landscape. In response he changed course to the west, hoping to regain his bearings by reaching the River Rhine. However, having already crossed over the frozen and indistinguishable Rhine at the moment he changed direction, he left German territory flying all the way to the River Meuse, the border in this area between Belgium and the Netherlands, and ended up circling Vught.
It was then that he appears to have inadvertently cut off the fuel supply to the plane’s engine by moving a lever inside the cockpit. The engine spluttered, then stopped, and Hoenmanns was forced to land in a nearby field at about 11:30 AM. The aircraft was severely damaged. Both wings were broken off when they hit two trees as he sped between them; the heavy engine tore off the nose section. The plane was a write/off, but Hoenmanns survived unscathed.
Had Hoenmanns been alone in the plane, nothing of great significance would likely have happened, apart from his internment for landing without permission in a neutral county. However, he had a passenger, one Major Helmuth Reinberger , who was responsible for organising the 7 Flieger Division´s supply, the formation that was to land paratroopers behind the Belgian lines at Namur on the day of the coming attack. Reinberger was going to Cologne for a staff meeting. The previous evening, over a drink in the mess, Hoenmanns had offered to fly him there. Usually, Reinberger would have had to make the tedious trip by train, but Hoenmanns needed some extra flying hours anyway and wanted to take his laundry to his wife in Cologne. Hoenmanns was unaware that Reinberger would be carrying documents related to the German plan for the attack on the Netherlands and Belgium, which on the day of the flight was decreed by Hitler to take place a week later on 17 January.
Hoenmanns only discovered that Reinberger was carrying secret documents when after landing, they asked a farmhand where they were, to be told that they had unknowingly crossed Dutch territory and landed just inside Belgium.
On hearing this Reinberger panicked and rushed back to the plane to secure his yellow pigskin briefcase, crying that he had secret documents that he must destroy immediately. To let him do this Hoenmanns, as a diversion, moved away from the plane. Reinberger first tried to set fire to the documents with his cigarette lighter but it malfunctioned; he then ran to the farmhand who gave him a single match. With this Reinberger hid behind a thicket and piled the papers on the ground to burn them. But soon two Belgian border guards arrived on bicycles, Sergeant Frans Habets and private Gerard Rubens. Seeing smoke coming from the bushes, Rubens rushed over to save the documents from being completely destroyed. Reinberger fled at first but allowed himself to be taken prisoner after two warning shots had been fired.
The two Germans were taken to the Belgian border guardhouse near Mechelen aan de Maas, Malines-sur-Meuse. There they were interrogated by Captain Arthur Rodrique, who placed the charred documents on a table. As a diversion once more, Hoenmanns asked the Belgian soldiers to let him use the toilet; Reinberger then tried to stuff the papers into a burning stove nearby. He succeeded but yelled with pain when lifting the extremely hot lid of the stove. Startled, Rodrique turned and snatched the papers from the fire, badly burning his hand in the process. The documents were now locked away in a separate room
. The failure to burn them made Reinberger realise that he would surely be shot, for letting the attack plan fall into the hands of the enemy. He decided to commit suicide and tried to grab Rodrique’s revolver. When the infuriated captain knocked him down, Reinberger burst into tears, shouting ‘I wanted your revolver to kill myself’. Hoenmanns supported Reinberger saying: ‘You can’t blame him. He’s a regular officer. He’s finished now.’
Two hours later officers from the Belgian intelligence service arrived, bringing the papers to the attention of their superiors in the late afternoon. At 7 p.m. Adolf Hitler, in response to the Mechelen Incident, concurred with the advice from the previous day of General Alfred Jodl, the Wehrmacht’s Chief of Operations, to call off the invasion of the Low Countries indefinitely. Generaloberst Alfred Jodl called off plans to execute the attack on the Low Countries three days early on January 14 and postponed them to January 15 or 16, 1940 to be decided as the circumstances demanded. That evening he received news that the Belgian and Dutch troops had been put on alert. This was attributed to the Mechelen Incident and the obvious approach of the Sixth Army under Field Marshal Walther von Reichenau..