1950 Navigation aids - Coastal Command

[Lyffe]

At 1620 GMT on 16 June 1950, Halifax RG843 of 202 Squadron crashed on the south-facing slope of Cruachán mountain on Achill Island (Country Mayo) whilst returning from a BISMUTH met reconnaissance flight. (BISMUTH was simply the name given to the triangular track which was flown.) The last position report received from the aircraft (immediately before impact) had placed its position to the southwest of Shannon - in fact the aircraft was actually 148 nautical miles ahead of the position calculated by the navigator. (Source F1180)

An additional comment at the bottom of the form notes "Navigation problems on present 'BISMUTH' tracks are being investigated. Orders issued that the third leg of the track above 51N (ie approach to land) be flown under VFR or safety height and not at the meteorological height of 950 mb (1800 ft)."

I can understand there being navigation difficulties during the war, but not in peace, and wonder if anyone could advise as to what technique would have been used for low-level maritime sorties during the late 1940s/early 1950s.

Alternatively I'd appreciate any thoughts as to why there should have been such a large navigational error after a 7.25 hour flight.

TIA
Brian

[Bill Walker]

Just a very general answer about nav errors, but long times spent at low altitudes, without visual references (i.e. over water) could produce large errors in position if exact winds are not known, and if radio aids are not available due to the low altitude, and/or if dead reckoning navigation is not done exactly right.

Maybe someone can comment on the status of LORAN or other radio nav aids in the UK in this time period. I know that LORAN was introduced gradually after the war in North America, so there were large areas without long range radio nav aids up into the 1950s. Other radio aids of the era, like ADF using aviation beacons or other radio transmitters had range limitations at lower altitudes. At 1800 ft I would expect ADF to be useless beyond about 50 to 100 miles from a North American transmitter.

[robstitt]

Hi Brian:

Not sure how much of this is useful but it refers to Fortress Met flights late 1944 and into 1945...

The Fortresses were also equipped with Gee, LORAN and an Air Position Indicator (API) to assist with navigation over the ocean.

Eric Jones was a navigator with 519 Sqn and describes a typical Met flight:

“Met flights were flown at a set pressure altitude. The outbound and return legs were flown at 950
millibars, or around 1,500 to 1,800ft, with a 250 nautical mile top leg at the terminal position flown at
500 millibars. The box climb prior to the top leg actually went up to 400mb – about 23,000ft (7,620m)
– with a descent along the leg to 500 millibars, followed by a box descent at the end of that leg for the
homeward trip. This requirement often meant flying in cloud for long periods. While within range of
Gee this was no problem. LORAN was also a godsend under these conditions but signal reception was
often less than ideal. During much of our time on 519, the LORAN signal from Iceland was weak or
could not be received… I believe the main aerial was damaged by storms and it was using a temporary
aerial. The other transmitters, based in the UK, gave a narrow angle of intercept of their position lines,
reducing the accuracy for the navigator. Skywaves could be difficult to measure due to fading or rising
up on the horizontal time base, but after flying in cloud or between layers for perhaps hours, it was the
best, and sometimes the only available navigation aid.

We were encouraged to maintain radio silence as much as possible, except when transmitting Met
information to base. On the twins - Venturas and Hudsons - we usually allowed ourselves the luxury of
calling for a bearing from the DF station at Kirkwall in the Orkneys soon after we set course for home,
as that was virtually the track we had to achieve. We may have done the same on the B-17 but it was
far less important as we had LORAN, which was often far from perfect, and Gee, which was very good,
for the last, say, 100 miles, depending on altitude, to straighten us up if we were off track.”

Sad to say Eric is no longer with us.

Regards:

Robert

[Dick]

Hi Brian
As indicated by Rob and Bill, oversea nav was far from exact, particularly using Dead Reckoning and it didnt change a lot postwar. Both Gee and Loran ought to have been available but were susceptible to weather and variable performance. Given where the Nav thought they were, they might have had the chance to use a Non Directional beacon on Shannon Airport which was, at the time, a more frequently used stopover for N Atlantic traffic, given the available types of aircraft, and it could have shown that the a/c was NW- NNW of Shannon and not SW as the Nav believed.It could have been enough to make the Nav wary.There was a further medium range aid available at the time in the shape of the German developed Consol chain which was initially set up to assist U-Boats. In the 1950's there were transmitters at Quimper and Ploneis in W France,and at 3 locations in W Spain and I used it as late as 1960 as a Signaller on Shackletons.It was very time consuming to use and hardly a tactical aid but it could have refined the navigation on the longer legs of the Bismuth. Did the Halifax retain any airborne search radar from it's WW2 roots? This could have given very accurate position fixes from nearby coastlines which would show up well enough for "map reading" and might have been fitted for dense cloud warning on a Met flight.
Regards
Dick

[Lyffe]

Thank you all gentlemen, you've all confirmed what I suspected (although I couldn't have described the finer points as you have.)

It was a Mk VI Halifax but I don't know if it was equipped with an airborne search radar - it's a possibility since 202 Sqn occasionally flew ASR missions.

The aircraft left Aldergrove at 0900 GMT flying to a point at approximately 54.5N 10.5W, then direct to 48.2N 20.5W which it reached at 1200 GMT (an approximate total distance of 650 nm). An ascent was made to 18000 ft at this position (taking 30-45 minutes) then it turned ENE to 49.5N 14.7W (approx 270 nm), at which point it made a descent to 1800 ft (say another 30-45 minutes.) From there the final leg was a straight line to approx 54.5N 10.5W (approximately 375 nm); it crashed on Achill Island (just south of this point) at 1620 GMT

The two maritime positions/times are taken from met reports published daily by the Met Office in the 'Daily Aerological Record'; the take-off time comes from the ORB and F1180, the crash time from the F1180.

I imagine the 18000 ft ascent and descent positions would be accurate in view of the navaids you've described.

I estimate the average speed from Aldergrove to the top of the descent at 1345 GMT to be about 220 knots, but from the bottom of the descent (at approximately 1420 GMT) to Achill Island only 185 knots, yet the F1180 records that just before the crash a position report placed the aircraft still 148 nm to the southwest - or only halfway along the leg. The 1800 ft wind was effectively a beam wind of about 300/10-15 knots throughout the sortie, so any thoughts of a headwind can be discarded.

It's difficult to imagine a navigator making such a huge error, yet the F1180 twice refers to on-going navigation problems.

Very strange.

Brian