Post by volkerboehme on Feb 27, 2009 0:25:15 GMT -5
This question deserves an answer which fully illustrates the real and rapidly changing provision of European air services by Imperial Airways 1938-39 and the interesting and diverse simulation opportunities offered. I will also take the opportunity to address the decline of Croydon raised in this forum a month or so ago. The vast majority of Imperial Airways route mileage was outside Europe of course, and they were not the only London based airline flying to most of the European destinations mentioned below. In 1938-39 four different British airlines competed with one another, and many foreign airlines, on the highly lucrative London - Paris routes alone.
In January 1938 Imperial Airways had only one British landplane hub (at Croydon) and had only six landplanes based there, but as we shall see by August 1939 Croydon had become home to twenty-four four engined Imperial Airways landplanes. This stands in stark contrast to the United States where the only four engined land based propliner was the experimental DC-4E making a few proving flights with UAL before being rejected. The B-307 Stratoliner did not enter service until 1940.
Prior to the outbreak of war Imperial Airways passenger landplane services from Croydon to Europe throughout 1938 - 39 were;
C - Paris
C - Basle - Zurich
C - Ostende
C - Brussels
C - Brussels - Cologne
C - Brussels - Frankfurt - Prague - Vienna - Budapest
In January 1938 the two 39 passenger Short L.17s Scylla and Syrinx were providing most of the Imperial Airways capacity on the out and back Paris and Brussels routes. The four 39 passenger Handley Page H.P.42Ws were flying all the other services and augmenting capacity to Paris. However Imperial Airways was no longer the 'chosen instrument' for services to Europe and for most of 1938-39 Croydon was not the designated London euro hub. For most of 1938-39 British Airways (B.A.) was the 'chosen instrument' on European routes and Heston (later replaced by nearby Heathrow) was London's euro hub.
The newsreels do not show Prime Minister Chamberlain disembarking from an ancient biplane of Imperial Airways at Croydon as he returns from Munich in 1938. He disembarks from a British Airways' Lockheed L.14 at Heston. It has only 14 seats, but is is designed to cruise at 200 KTAS. From late 1938 B.A. Lockheed Super Electras replaced the Fiat G.18 Veloce as the fastest propliner serving London.
Nevertheless Imperial Airways still offered competing landplane services to Europe from Croydon. These were barely augmented by a single passenger flying boat service. This was nominally from the port of Southampton, where the terminus was located for ease of customs and immigration processing, but with the boats actually operating from the Imperial Airways facilities at Hythe on the other side of the estuary. In 1938-39 the port of Southampton itself was too busy with all kinds of shipping to accommodate flying boat landing lanes and did not offer instrument approaches. By 1938 Hythe could handle two flying boats at a time, but rarely needed to. The single low capacity eight times per week Imperial Airways flying boat service through Europe was;
Hythe - (Macon or St.Nazaire) - Marseilles - Rome - Brindisi - Athens - (Mirabella Bay) onward to Alexandria and thence all points of the Empire.
Macon was a potential refuelling stop on the Saone River near Lyons, about half way down a nearly direct track to Marseilles. It was mandatory when headwinds prevailed in either direction. Macon was not an (air) port. It had no customs and immigration facilities. A harbour is not a port and an airfield/ aerodrome/ aquadrome is not an airport unless it has customs and immigration facilities. No one could embark or disembark at Macon. St. Nazaire was a port and a frequent refuelling stop situated on the Loire estuary, on the Atlantic coast of France. It was mandatory as a weather detour when high ground over France on the direct track was forecast to be in cloud. Even with favourable weather London - Alexandria was a two day journey by air before WW2. Mirabella Bay in the north east of Crete was the headwind diversion on the last European leg of the Empire routes from Athens to Alexandria. The landing lanes and mooring buoys were in the far south west of the bay just outside the port of Agios Nikolaos which provided the necessary customs and immigration facilities. Even when they were not required as refuelling stops, weather permitting, upon sufficient additional payment, passage could be pre booked to the optional ports of call at St Nazaire and Agios Nikolaos as 'on request' stops. The route used on the Imperial Airways trans European flying boat services had varied greatly prior to 1938, but in 1938-39 it was consistently as above.
From August 1939 Imperial Airways began scheduled passenger services to the British Dominion of Canada, via the European nation of Ireland, using Empire boats flying Hythe - Shannon (actually Foynes on the River Shannon) and beyond. However the long range Empire boats used on these scheduled North American Empire services were almost immediately needed to augment wartime passenger capacity to Alexandria. Empire boat services from Britain to Alexandria had begun in February 1937 and all landplane passenger services from Croydon to the Empire were terminated a month later. From then on all Imperial Airways aircraft based at Croydon served only Europe. From then onwards the majority of I.A. landplanes, of types never based in Europe, were based in Africa, or Asia, and never visited Europe. Some I.A. Empire boats were also based far from Britain and never visited Europe. From May 1937 in the British colony of Bermuda for instance.
The C class Empire boats carried huge quantities of mail, military dispatches and diplomatic bags to the Empire and therefore had a maximum of seventeen passenger seats in pre war service. Numerically they were a large part of the entire Imperial Airways fleet based in Britain but they provided very little passenger capacity. Imperial Airways operated a total of twenty-eight C class Empire boats 1937-39, but nine were quickly lost in accidents and so the total number of Empire boats in service did not reach nineteen until August 1939; and not all were based in Britain. Their safety record was appalling compared to the huge ancient lumbering landplanes operating from Croydon.
Now we must remember that all the Hythe based boats continued far beyond Egypt to South Africa, India and Australia. Each boat 'based' at Hythe only visited Britain twice per month! The number 'based' at Hythe allowed only eight departures per week generating only 136 seats per week towards Continental Europe. Very few air passengers ever travelled over Europe by flying boat, even in 1938-39; and almost none of them were bound for Europe. Flying boat passengers were bound for the Empire upon which the sun never set that lay far beyond the River Shannon and Mirabella Bay.
Meanwhile five of the six 39 passenger biplanes at Croydon in January 1938 make multiple sorties into Europe each day. Even in January 1938 the six huge ancient biplanes at Croydon are capable of offering around 3000 passenger departures per week to Europe. To the British air traveler of 1938 flying boats had very little relevance to European air services, even if they were only considering Imperial Airways services to Europe. The British frequent flyer and cargo shipper of 1938 knew that seven of the sixteen British airlines flying scheduled air services already offered scheduled services to Europe.
Imperial Airways was no longer the chosen instrument for European air services, but they were well aware that both the H.P.42W and S.17L were horribly out of date. They had planned to replace them with four 40 seat Armstrong Whitworth Ensigns ordered in 1936. However like most British propliners the Ensign had many flaws. It's original engines were so unreliable that none flew scheduled passenger services from Croydon until October 1938 and even then they were used to augment, not replace, the huge ancient biplanes.
Ten more long range Ensigns with only 27 passenger seats, never intended for European services, were rejected for long haul use and were also relegated to the European routes above. So by August 1939 seven 27 seat and four 40 seat Ensigns were based at Croydon, still working alongside the six 39 seat biplanes. Most Ensigns were still so problematic that they were barely usable, but Imperial Airways' available capacity from Croydon into Europe had thus reached a 'practical' 4000+ seats per weak versus 136 from Hythe.
However from November 1938 Imperial Airways were also adding the de Havilland Albatross as a premium fare 22 seat express service aircraft on the premium Euro routes to allow effective competition with British Airways' 14 seat Lockheeds operating from Heston. Those premium routes were to Paris, Brussels and Basle - Zurich. The 40 seat Ensign was designed to cruise at 147 KTAS, but the 22 seat Albatross was designed to cruise at 182 KTAS. During 1938-39 Imperial Airways took delivery of seven Albatrosses, two of which were express mailplanes with no seats.
In April 1939 all airline departures from all London airports to all Paris airports peaked at 35 per day. With Ensigns and Albatrosses steadily joining the fleet. Imperial Airways' 'practical' passenger capacity from Croydon to Europe exceeded 5000 seats per week by August 1939, but was still only 136 seats per week from Hythe.
Unlike Heston, Croydon offered the most advanced instrument approach facilities, but Croydon never had hard runways. Wet grass does not aid braking. More to the point Croydon was already surrounded by urban housing and the runways were already short, even by contemporary standards. The longest runway at Croydon (17/35) was only 3600 feet and was at right angles to the prevailing westerly winds (roughly 260). Nearby Redhill (EGKR), which is still a commercial airfield, (but not an airport), is much the same size today as the lesser runways at Croydon were before it closed in the fifties, so if you want to know how cramped Croydon was just fly a Fiat G.18 Veloce out of Redhill in FS9.
During the 1930s Imperial Airways were required to offer frequent round the clock services, in all weathers, from the tiny runways at Croydon into Europe using very high capacity four engined propliners. Those aeroplanes required huge wing area to cope with the short wet grass runways, at night, in fog. That made them slow, but they were very safe, and they shifted a lot of passengers with every departure. Let's pause to remember that the largest propliner flying scheduled services in the entire US commercial landplane fleet in 1939 was the max 28 seat DC-3. Let's remember that the four engined Boeing B307 Stratoliner does not enter scheduled passenger service with PAA until October 1940 and then has only 30 passenger seats. Its design cruise TAS just matches the 1937 Fiat G.18 Veloce at 186 KTAS.
All foreign air services from, to and through Germany ended on 2nd September 1939. All surviving Imperial Airways Croydon services were nominally relocated to Bristol Whitchurch from that day (but we must use Lulsgate = EGGD in MSFS). All Hythe terminus services including the Shannon service relocated to Poole Harbour near Bournemouth. Bristol was however unable to cope without expansion of its facilities and so in practice the Imperial Airways fleet dispersed to several British hubs during the last four months of 1939.
The two Albatross mailplanes and some Ensigns had already made unscheduled air mail only flights to Alexandria during 1938. There had been no landplane passenger services to the Empire after March 1937, but the outbreak of war made air communication with the distant Empire ever more vital. Most of the Albatross fleet now moved to Shoreham (EGKA) from 22nd September 1939 flying;
Shoreham - Bordeaux - Marseilles - Tunis - Malta - - Egypt - - India.
This added Malta back to the Imperial Airways European destinations, and the addition of Bordeaux to the Imperial Airways ports of call increased the number of French cities civilians could use as ports of entry to five. Basle despite being Switzerland's largest port has no airport and Switzerland runs half of the airport at Mulhouse in France. Even today passengers must still pass through customs and immigration just to cross the airport from side to side at Mulhouse. These new Empire landplane services from Shoreham augmented, not replaced, the critically low capacity Short Empire boat services now based at Poole.
The other Albatrosses were now based at Bristol and flew Bristol - Shannon (airport) and Bristol - Lisbon (airport) adding another European destination and interlining with the infrequent PAA flying boat services to Lisbon (harbour), since PAA services soon no longer continued to Marseilles.
From September 1939 two or more of the four H.P.42s were relocated to Exeter (EGTE) to relieve the pressure on Bristol and all four were operating from Bristol and Exeter in support of the British Expeditionary Force (B.E.F.) and the RAF Advanced Air Striking Force in France during the last four months of 1939. Nominally based in Bristol most of the eleven Ensigns so far delivered actually moved to Coventry (EGBE) and during the last four months of 1939 they too were flying logistic support for the B.E.F. in north east France. Once the phony war ended three Ensigns were soon lost to enemy fire.
The most frequent destinations for all fifteen Imperial Airways propliners supporting the BEF during 1939 would have been Cambrai (LFQI) and, Lille (LFQQ) in the area where the BEF were massing ready to resist the expected German thrust though Belgium. For simulation purposes assume that Ensigns based at Coventry must route to Southampton to avoid the London ADIZ before following the coast via Shoreham to Lydd and only then crossing to Saint Inglevert (NDB = 387 Kcs) and onward to Lille (332 Kcs) or Cambrai (use Valenciennes = 317 Kcs) always taking great care not to infringe Belgian airspace. Accessing Lille without penetrating Belgian airspace requires particular care and planning. The HP 42Ws from Exeter and Bristol should also route over Southampton and then as above. These logistics flights were not open to civilians.
The two Short L.17s were withdrawn from Imperial Airways use as soon as war broke out.
Due to the Eastern England Air Defence Free Fire Zone all foreign airlines were forced to switch from Croydon to Shoreham and had to avoid overflying the UK mainland en route to Shoreham from 2nd September 1939 onwards. Some may have been forced to relocate earlier. Propliners did not yet have transponders and from September 1939 any aircraft near London not squawking the correct code of the day was shot down without identification. There were no London airports during WW2.
Deprived of 'chosen instrument' status, and with replacement by Heston underway even before WW2, and starved of investment from then onwards, Croydon never recovered its pre 1938 premier airport status. Seven London airports namely Heathrow (9000 feet), Dunsfold (6123 feet - but cargo only), Blackbushe (6000 feet), Northolt (5520 feet), Bovingdon (4920 feet), Southend (4200 feet) and Gatwick (4200 feet) were all much larger than Croydon after WW2. By the time Croydon reopened for civilian use after the war it had become London's eighth airport with few, and then quite soon no scheduled passenger services at all. All those post war land airports serving just one city at the same time may help us to come to terms with the reality that large flying boats were lovely to fly in, had great propaganda value, and were a potentially useful long range strategic asset, but were functionally useless as commercial aircraft. Only the 'chosen instruments' of the wealthiest nations ever received the huge subsidies needed to operate them in significant numbers.
In the whole of aviation history the only large scale operators of large 'commercial' flying boats were PAA, IA and BOAC, (formed by merger of IA and BA in 1940). They generated very little capacity using them, even though BOAC eventually employed around thirty large flying boats (around twice as many as PAA). There is a good reason that large 'commercial' flying boats were rare outside the British Empire and did not last long. They were unsafe, they served the propaganda needs of major governments, and the travel needs of a privileged few. They were an evolutionary dead end in aviation history. Despite the impression which may be conveyed by browsing the internet, the vast majority of Imperial Airways' passengers flew in landplanes. The role played by 'commercial' flying boats in aviation history is mostly romantic propaganda which does not address their critically low passenger capacity and awful safety record.
FSAviator.
In January 1938 Imperial Airways had only one British landplane hub (at Croydon) and had only six landplanes based there, but as we shall see by August 1939 Croydon had become home to twenty-four four engined Imperial Airways landplanes. This stands in stark contrast to the United States where the only four engined land based propliner was the experimental DC-4E making a few proving flights with UAL before being rejected. The B-307 Stratoliner did not enter service until 1940.
Prior to the outbreak of war Imperial Airways passenger landplane services from Croydon to Europe throughout 1938 - 39 were;
C - Paris
C - Basle - Zurich
C - Ostende
C - Brussels
C - Brussels - Cologne
C - Brussels - Frankfurt - Prague - Vienna - Budapest
In January 1938 the two 39 passenger Short L.17s Scylla and Syrinx were providing most of the Imperial Airways capacity on the out and back Paris and Brussels routes. The four 39 passenger Handley Page H.P.42Ws were flying all the other services and augmenting capacity to Paris. However Imperial Airways was no longer the 'chosen instrument' for services to Europe and for most of 1938-39 Croydon was not the designated London euro hub. For most of 1938-39 British Airways (B.A.) was the 'chosen instrument' on European routes and Heston (later replaced by nearby Heathrow) was London's euro hub.
The newsreels do not show Prime Minister Chamberlain disembarking from an ancient biplane of Imperial Airways at Croydon as he returns from Munich in 1938. He disembarks from a British Airways' Lockheed L.14 at Heston. It has only 14 seats, but is is designed to cruise at 200 KTAS. From late 1938 B.A. Lockheed Super Electras replaced the Fiat G.18 Veloce as the fastest propliner serving London.
Nevertheless Imperial Airways still offered competing landplane services to Europe from Croydon. These were barely augmented by a single passenger flying boat service. This was nominally from the port of Southampton, where the terminus was located for ease of customs and immigration processing, but with the boats actually operating from the Imperial Airways facilities at Hythe on the other side of the estuary. In 1938-39 the port of Southampton itself was too busy with all kinds of shipping to accommodate flying boat landing lanes and did not offer instrument approaches. By 1938 Hythe could handle two flying boats at a time, but rarely needed to. The single low capacity eight times per week Imperial Airways flying boat service through Europe was;
Hythe - (Macon or St.Nazaire) - Marseilles - Rome - Brindisi - Athens - (Mirabella Bay) onward to Alexandria and thence all points of the Empire.
Macon was a potential refuelling stop on the Saone River near Lyons, about half way down a nearly direct track to Marseilles. It was mandatory when headwinds prevailed in either direction. Macon was not an (air) port. It had no customs and immigration facilities. A harbour is not a port and an airfield/ aerodrome/ aquadrome is not an airport unless it has customs and immigration facilities. No one could embark or disembark at Macon. St. Nazaire was a port and a frequent refuelling stop situated on the Loire estuary, on the Atlantic coast of France. It was mandatory as a weather detour when high ground over France on the direct track was forecast to be in cloud. Even with favourable weather London - Alexandria was a two day journey by air before WW2. Mirabella Bay in the north east of Crete was the headwind diversion on the last European leg of the Empire routes from Athens to Alexandria. The landing lanes and mooring buoys were in the far south west of the bay just outside the port of Agios Nikolaos which provided the necessary customs and immigration facilities. Even when they were not required as refuelling stops, weather permitting, upon sufficient additional payment, passage could be pre booked to the optional ports of call at St Nazaire and Agios Nikolaos as 'on request' stops. The route used on the Imperial Airways trans European flying boat services had varied greatly prior to 1938, but in 1938-39 it was consistently as above.
From August 1939 Imperial Airways began scheduled passenger services to the British Dominion of Canada, via the European nation of Ireland, using Empire boats flying Hythe - Shannon (actually Foynes on the River Shannon) and beyond. However the long range Empire boats used on these scheduled North American Empire services were almost immediately needed to augment wartime passenger capacity to Alexandria. Empire boat services from Britain to Alexandria had begun in February 1937 and all landplane passenger services from Croydon to the Empire were terminated a month later. From then on all Imperial Airways aircraft based at Croydon served only Europe. From then onwards the majority of I.A. landplanes, of types never based in Europe, were based in Africa, or Asia, and never visited Europe. Some I.A. Empire boats were also based far from Britain and never visited Europe. From May 1937 in the British colony of Bermuda for instance.
The C class Empire boats carried huge quantities of mail, military dispatches and diplomatic bags to the Empire and therefore had a maximum of seventeen passenger seats in pre war service. Numerically they were a large part of the entire Imperial Airways fleet based in Britain but they provided very little passenger capacity. Imperial Airways operated a total of twenty-eight C class Empire boats 1937-39, but nine were quickly lost in accidents and so the total number of Empire boats in service did not reach nineteen until August 1939; and not all were based in Britain. Their safety record was appalling compared to the huge ancient lumbering landplanes operating from Croydon.
Now we must remember that all the Hythe based boats continued far beyond Egypt to South Africa, India and Australia. Each boat 'based' at Hythe only visited Britain twice per month! The number 'based' at Hythe allowed only eight departures per week generating only 136 seats per week towards Continental Europe. Very few air passengers ever travelled over Europe by flying boat, even in 1938-39; and almost none of them were bound for Europe. Flying boat passengers were bound for the Empire upon which the sun never set that lay far beyond the River Shannon and Mirabella Bay.
Meanwhile five of the six 39 passenger biplanes at Croydon in January 1938 make multiple sorties into Europe each day. Even in January 1938 the six huge ancient biplanes at Croydon are capable of offering around 3000 passenger departures per week to Europe. To the British air traveler of 1938 flying boats had very little relevance to European air services, even if they were only considering Imperial Airways services to Europe. The British frequent flyer and cargo shipper of 1938 knew that seven of the sixteen British airlines flying scheduled air services already offered scheduled services to Europe.
Imperial Airways was no longer the chosen instrument for European air services, but they were well aware that both the H.P.42W and S.17L were horribly out of date. They had planned to replace them with four 40 seat Armstrong Whitworth Ensigns ordered in 1936. However like most British propliners the Ensign had many flaws. It's original engines were so unreliable that none flew scheduled passenger services from Croydon until October 1938 and even then they were used to augment, not replace, the huge ancient biplanes.
Ten more long range Ensigns with only 27 passenger seats, never intended for European services, were rejected for long haul use and were also relegated to the European routes above. So by August 1939 seven 27 seat and four 40 seat Ensigns were based at Croydon, still working alongside the six 39 seat biplanes. Most Ensigns were still so problematic that they were barely usable, but Imperial Airways' available capacity from Croydon into Europe had thus reached a 'practical' 4000+ seats per weak versus 136 from Hythe.
However from November 1938 Imperial Airways were also adding the de Havilland Albatross as a premium fare 22 seat express service aircraft on the premium Euro routes to allow effective competition with British Airways' 14 seat Lockheeds operating from Heston. Those premium routes were to Paris, Brussels and Basle - Zurich. The 40 seat Ensign was designed to cruise at 147 KTAS, but the 22 seat Albatross was designed to cruise at 182 KTAS. During 1938-39 Imperial Airways took delivery of seven Albatrosses, two of which were express mailplanes with no seats.
In April 1939 all airline departures from all London airports to all Paris airports peaked at 35 per day. With Ensigns and Albatrosses steadily joining the fleet. Imperial Airways' 'practical' passenger capacity from Croydon to Europe exceeded 5000 seats per week by August 1939, but was still only 136 seats per week from Hythe.
Unlike Heston, Croydon offered the most advanced instrument approach facilities, but Croydon never had hard runways. Wet grass does not aid braking. More to the point Croydon was already surrounded by urban housing and the runways were already short, even by contemporary standards. The longest runway at Croydon (17/35) was only 3600 feet and was at right angles to the prevailing westerly winds (roughly 260). Nearby Redhill (EGKR), which is still a commercial airfield, (but not an airport), is much the same size today as the lesser runways at Croydon were before it closed in the fifties, so if you want to know how cramped Croydon was just fly a Fiat G.18 Veloce out of Redhill in FS9.
During the 1930s Imperial Airways were required to offer frequent round the clock services, in all weathers, from the tiny runways at Croydon into Europe using very high capacity four engined propliners. Those aeroplanes required huge wing area to cope with the short wet grass runways, at night, in fog. That made them slow, but they were very safe, and they shifted a lot of passengers with every departure. Let's pause to remember that the largest propliner flying scheduled services in the entire US commercial landplane fleet in 1939 was the max 28 seat DC-3. Let's remember that the four engined Boeing B307 Stratoliner does not enter scheduled passenger service with PAA until October 1940 and then has only 30 passenger seats. Its design cruise TAS just matches the 1937 Fiat G.18 Veloce at 186 KTAS.
All foreign air services from, to and through Germany ended on 2nd September 1939. All surviving Imperial Airways Croydon services were nominally relocated to Bristol Whitchurch from that day (but we must use Lulsgate = EGGD in MSFS). All Hythe terminus services including the Shannon service relocated to Poole Harbour near Bournemouth. Bristol was however unable to cope without expansion of its facilities and so in practice the Imperial Airways fleet dispersed to several British hubs during the last four months of 1939.
The two Albatross mailplanes and some Ensigns had already made unscheduled air mail only flights to Alexandria during 1938. There had been no landplane passenger services to the Empire after March 1937, but the outbreak of war made air communication with the distant Empire ever more vital. Most of the Albatross fleet now moved to Shoreham (EGKA) from 22nd September 1939 flying;
Shoreham - Bordeaux - Marseilles - Tunis - Malta - - Egypt - - India.
This added Malta back to the Imperial Airways European destinations, and the addition of Bordeaux to the Imperial Airways ports of call increased the number of French cities civilians could use as ports of entry to five. Basle despite being Switzerland's largest port has no airport and Switzerland runs half of the airport at Mulhouse in France. Even today passengers must still pass through customs and immigration just to cross the airport from side to side at Mulhouse. These new Empire landplane services from Shoreham augmented, not replaced, the critically low capacity Short Empire boat services now based at Poole.
The other Albatrosses were now based at Bristol and flew Bristol - Shannon (airport) and Bristol - Lisbon (airport) adding another European destination and interlining with the infrequent PAA flying boat services to Lisbon (harbour), since PAA services soon no longer continued to Marseilles.
From September 1939 two or more of the four H.P.42s were relocated to Exeter (EGTE) to relieve the pressure on Bristol and all four were operating from Bristol and Exeter in support of the British Expeditionary Force (B.E.F.) and the RAF Advanced Air Striking Force in France during the last four months of 1939. Nominally based in Bristol most of the eleven Ensigns so far delivered actually moved to Coventry (EGBE) and during the last four months of 1939 they too were flying logistic support for the B.E.F. in north east France. Once the phony war ended three Ensigns were soon lost to enemy fire.
The most frequent destinations for all fifteen Imperial Airways propliners supporting the BEF during 1939 would have been Cambrai (LFQI) and, Lille (LFQQ) in the area where the BEF were massing ready to resist the expected German thrust though Belgium. For simulation purposes assume that Ensigns based at Coventry must route to Southampton to avoid the London ADIZ before following the coast via Shoreham to Lydd and only then crossing to Saint Inglevert (NDB = 387 Kcs) and onward to Lille (332 Kcs) or Cambrai (use Valenciennes = 317 Kcs) always taking great care not to infringe Belgian airspace. Accessing Lille without penetrating Belgian airspace requires particular care and planning. The HP 42Ws from Exeter and Bristol should also route over Southampton and then as above. These logistics flights were not open to civilians.
The two Short L.17s were withdrawn from Imperial Airways use as soon as war broke out.
Due to the Eastern England Air Defence Free Fire Zone all foreign airlines were forced to switch from Croydon to Shoreham and had to avoid overflying the UK mainland en route to Shoreham from 2nd September 1939 onwards. Some may have been forced to relocate earlier. Propliners did not yet have transponders and from September 1939 any aircraft near London not squawking the correct code of the day was shot down without identification. There were no London airports during WW2.
Deprived of 'chosen instrument' status, and with replacement by Heston underway even before WW2, and starved of investment from then onwards, Croydon never recovered its pre 1938 premier airport status. Seven London airports namely Heathrow (9000 feet), Dunsfold (6123 feet - but cargo only), Blackbushe (6000 feet), Northolt (5520 feet), Bovingdon (4920 feet), Southend (4200 feet) and Gatwick (4200 feet) were all much larger than Croydon after WW2. By the time Croydon reopened for civilian use after the war it had become London's eighth airport with few, and then quite soon no scheduled passenger services at all. All those post war land airports serving just one city at the same time may help us to come to terms with the reality that large flying boats were lovely to fly in, had great propaganda value, and were a potentially useful long range strategic asset, but were functionally useless as commercial aircraft. Only the 'chosen instruments' of the wealthiest nations ever received the huge subsidies needed to operate them in significant numbers.
In the whole of aviation history the only large scale operators of large 'commercial' flying boats were PAA, IA and BOAC, (formed by merger of IA and BA in 1940). They generated very little capacity using them, even though BOAC eventually employed around thirty large flying boats (around twice as many as PAA). There is a good reason that large 'commercial' flying boats were rare outside the British Empire and did not last long. They were unsafe, they served the propaganda needs of major governments, and the travel needs of a privileged few. They were an evolutionary dead end in aviation history. Despite the impression which may be conveyed by browsing the internet, the vast majority of Imperial Airways' passengers flew in landplanes. The role played by 'commercial' flying boats in aviation history is mostly romantic propaganda which does not address their critically low passenger capacity and awful safety record.
FSAviator.