The UK–Lisbon service operated up to four times per week.
From 20 September 1940, passengers were flown from Whitchurch (although Heston continued as the London terminus for KLM from 26 June till 20 September 1940), and for Lisbon, the pre-war grass airfield at Sintra was used until October 1942, when the new runway was ready at Portela Airport, on the northern edge of Lisbon.
By June 1943, over 500 KLM/BOAC flights had carried 4,000 passengers.

Originally, five Douglas DC-3s and one Douglas DC-2 airliner were available, but with the loss of a DC-3 on 20 September 1940 in a landing accident at Heston, and the destruction of another DC-3 in November 1940 by Luftwaffe bombing at Whitchurch, only four aircraft remained: DC-2 G-AGBH Edelvalk (ex-PH-ALE), DC-3 G-AGBD Buizerd (ex-PH-ARB), DC-3 G-AGBE Zilverreiger (ex-PH-ARZ), and DC-3 G-AGBB Ibis (ex-PH-ALI).
In 1939, with war tensions in Europe increasing, KLM had painted their DC-2s and DC-3s bright orange to mark them clearly as civilian aircraft.
BOAC repainted the aircraft in camouflage, with British civil markings and red/white/blue stripes like all BOAC aircraft, but without the Union Flag.
They were later marked with their Dutch bird names under the cockpit windows.
The interiors remained in KLM colours and markings.

British and German civilian aircraft operated from the same facilities at Portela and Allied and Axis spies, including British, German, Soviet, and American, watched the traffic.
This was especially the case for the Lisbon–Whitchurch route, which frequently carried agents and escaped POWs to Britain.
German spies were posted at terminals to record who was boarding and departing flights on the Lisbon–Whitchurch route.
Harry Pusey, BOAC's operations officer in Lisbon between 1943 and 1944 described the area as "like Casablanca [the film], but twentyfold."
 According to CIA archives: "Most OSS operatives in Spain were handled out of Lisbon under nonofficial cover because the diplomatic staff in Madrid made a practice of identifying intelligence agents to the Spanish police."
The UK–Lisbon service operated up to four times per week. From 20 September 1940, passengers were flown from Whitchurch (although Heston continued as the London terminus for KLM from 26 June till 20 September 1940), and for Lisbon, the pre-war grass airfield at Sintra was used until October 1942, when the new runway was ready at Portela Airport, on the northern edge of Lisbon. By June 1943, over 500 KLM/BOAC flights had carried 4,000 passengers.
Originally, five Douglas DC-3s and one Douglas DC-2 airliner were available, but with the loss of a DC-3 on 20 September 1940 in a landing accident at Heston, and the destruction of another DC-3 in November 1940 by Luftwaffe bombing at Whitchurch, only four aircraft remained: DC-2 G-AGBH Edelvalk (ex-PH-ALE), DC-3 G-AGBD Buizerd (ex-PH-ARB), DC-3 G-AGBE Zilverreiger (ex-PH-ARZ), and DC-3 G-AGBB Ibis (ex-PH-ALI). In 1939, with war tensions in Europe increasing, KLM had painted their DC-2s and DC-3s bright orange to mark them clearly as civilian aircraft. BOAC repainted the aircraft in camouflage, with British civil markings and red/white/blue stripes like all BOAC aircraft, but without the Union Flag. They were later marked with their Dutch bird names under the cockpit windows. The interiors remained in KLM colours and markings.
British and German civilian aircraft operated from the same facilities at Portela and Allied and Axis spies, including British, German, Soviet, and American, watched the traffic. This was especially the case for the Lisbon–Whitchurch route, which frequently carried agents and escaped POWs to Britain. German spies were posted at terminals to record who was boarding and departing flights on the Lisbon–Whitchurch route. Harry Pusey, BOAC's operations officer in Lisbon between 1943 and 1944 described the area as "like Casablanca [the film], but twentyfold."  According to CIA archives: "Most OSS operatives in Spain were handled out of Lisbon under nonofficial cover because the diplomatic staff in Madrid made a practice of identifying intelligence agents to the Spanish police."
BOAC Flight 777