What kind of aircraft did he use as his getaway vehicle? I’d vote for Lisunov-2 (Li-2) – a Soviet-built licensed copy of American C-47 Skytrain (more commonly known as DC-3).
During the first weeks of Operation Barbarossa the German Army captured Soviet aircraft by the hundreds – right on their airfields (German tanks were advancing so fast that the Red Air Force simply had no time to evacuate its assets). According to the Soviet statistics that lied through its teeth all the time, all captured aircraft were lost in action (i.e. shot down by German fighters or AA fire).
Combat aircraft were destroyed (they were way too risky to use due to the “friendly fire” problem), but cargo planes were a different matter entirely – they could be safely operated deep in German territory (or by its numerous allies far from the Eastern front).
And not necessarily by KG 200, of course – although there were rumors that the latter did use Li-2 to drop off Abwehr agents behind the Soviet lines. Way behind, in fact.
The distance between Flensburg and Santander (probably the most convenient landing point as it was a home to Banco Santander – one of the largest banking institutions in the world) is 1500 km “as the crow flies”.
The ferry range of Li-2 (and with just one passenger on board it was exactly that) is 2,500 km – which allowed it to fly over the water, far from the “hunting grounds” of the Allied fighters (which the KG 200 pilots were Gross masters at avoiding regardless).
However, their skills were most likely not necessary as the getaway plane was surely repainted with Spanish Air Force colors and insignia. True, at that time Spain did not operate C-47s (it began to receive them in early 1950s), but the Allied fighter pilots did not know that.
All they knew (if they encountered the aircraft which was extremely unlikely) that they were seeing a Skytrain with the insignia of a neutral nation. The war was practically over (most likely, Himmler left Flensburg for Spain on May 5th – right after the meeting with Dönitz), Hitler was dead – so who cares about the lonely C-47?
Li-2 was extensively used for supplying the Soviet partisans because it could land on a forest meadow (and not a big one at that). Hence finding a place to land in Spain presented no problem whatsoever.
Assuming it took the longest possible route to avoid encounters with Allied fighters (just in case), it took Himmler’s getaway plane roughly ten hours to reach Spain. Having took off right after sunset, it landed a couple of hours after sunrise.
Even if it was noticed by anyone in German government (local or national, military or civilian) – or even by Ejército del Aire (Spanish Air Force) pilots, no one would have paid any attention.
No one knew for sure that Spain did not operate C-47 and the markings were obviously kosher. Knowing Himmler’s obsessive attention to even a miniscule detail, there is no doubt that the pilots were sufficiently fluent in both Spanish and English (in case they did encounter Allied fighters along the way).
On the ground Himmler (he most likely flew solo) was met by the local Nazi sympathizers and the SS security detail that arrived in Spain in advance. SS Reichsfuhrer (no one took Hitler’s order seriously) was promptly whisked away to a safe house in Santander (or nearby).
Where he spent some time waiting for a plastic surgeon and for another set of documents to arrive. However, there is a possibility that he went straight down to business with Banco de Santander (it is highly probably that Himmler brought with him to Spain a sizable cache of highly liquid financial assets).
The pilots took a short rest and soon took off again (they did not need refueling for the last leg of their journey). A few miles offshore they skillfully landed Li-2 on the water and let it sink.
An inflatable boat took them to the shore where they received new documents and in no time were on their way to Argentina. In Luftwaffe personnel files they were listed as killed in action shortly before the surrender of Germany.
Which means, that the man with an ID in the name of Sergeant Heinrich Hitzinger who “attempted to go into hiding” (but undertook a very strange journey on foot instead) was definitely not Heinrich Himmler. But his impersonator, his double and – for all practical purposes – his savior.