A question about a Comet 4
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A question about a Comet 4
Hello everybody,
I'm new here. I'm not a professional. I've just registered here because I have some questions for professionals; excuse me if my questions are silly questions, but I need some answers to try to understand some things about a Comet 4.
My question is into the context of 1970. I want to know what kind of ariborne problems you think could be related to these malfunctions:
-The Doppler it's out of action.
-The 1 VOR set it's not working properly.
Thanks in advance.
I'm new here. I'm not a professional. I've just registered here because I have some questions for professionals; excuse me if my questions are silly questions, but I need some answers to try to understand some things about a Comet 4.
My question is into the context of 1970. I want to know what kind of ariborne problems you think could be related to these malfunctions:
-The Doppler it's out of action.
-The 1 VOR set it's not working properly.
Thanks in advance.
If it had Doppler, this would indicate a BEA Comet 4b.
Both things you mention are nav systems but if both are out of action, the aircraft would be unable to use normal ground based navigation systems of the time and would be unable to fly on airways.
I think doppler on its own was allowed, but you would need 2 VORs in the absence of doppler.
Both things you mention are nav systems but if both are out of action, the aircraft would be unable to use normal ground based navigation systems of the time and would be unable to fly on airways.
I think doppler on its own was allowed, but you would need 2 VORs in the absence of doppler.
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Thanks a lot for your answer. The aircraft was a standad production HS Comet 4 (1959). Let me add some more questions; always into the context of 1970's.
About the doppler;
Althought the doppler was not a mandatory equipment, it was then a common thing not to repair/replace this equipment? The doppler was out of action, at least, more than 10 days since de malfunction was detected. What is your opinion about?
About the VOR set;
-The aircraft was provided with duplicated Marconi AD 704/706 ILS/VOR, and the number 1 VOR set it has been repaired two times, because during the previous flights it was not working properly. The set it's replaced and seems to work properly. Apparently.
-One day after the VOR set number 1 was replaced, the aircraft was flying out of track without the knowledge of the crew. This is a fact.
My questions about;
-It was a mandatory thing to inform the crew that this equipment has been just replaced? In another words, they crew could be using the 1 VOR set without knowing anything about the previous malfunctions?
-It's a common thing to use both VOR equipments during the flight? Or if the crew trust in VOR set number one, because it seems to work properly, then they don't have any reason to use the second VOR set?
-It is possible that a malfunction in the VOR set mislead the crew, without any chance to detect that the equipment it's not working properly, and while they are convinced they are flying over/or in direction to a radiobeacon included in their flight plan, in fact they are flying over /or in direction to another radiobeacon not included in their flight plan?
-Apart from an eye contact with the aircraft on a radar screen, there was, by that time, another on the ground support that was able to determine the real position of the aircraft?
About the doppler;
Althought the doppler was not a mandatory equipment, it was then a common thing not to repair/replace this equipment? The doppler was out of action, at least, more than 10 days since de malfunction was detected. What is your opinion about?
About the VOR set;
-The aircraft was provided with duplicated Marconi AD 704/706 ILS/VOR, and the number 1 VOR set it has been repaired two times, because during the previous flights it was not working properly. The set it's replaced and seems to work properly. Apparently.
-One day after the VOR set number 1 was replaced, the aircraft was flying out of track without the knowledge of the crew. This is a fact.
My questions about;
-It was a mandatory thing to inform the crew that this equipment has been just replaced? In another words, they crew could be using the 1 VOR set without knowing anything about the previous malfunctions?
-It's a common thing to use both VOR equipments during the flight? Or if the crew trust in VOR set number one, because it seems to work properly, then they don't have any reason to use the second VOR set?
-It is possible that a malfunction in the VOR set mislead the crew, without any chance to detect that the equipment it's not working properly, and while they are convinced they are flying over/or in direction to a radiobeacon included in their flight plan, in fact they are flying over /or in direction to another radiobeacon not included in their flight plan?
-Apart from an eye contact with the aircraft on a radar screen, there was, by that time, another on the ground support that was able to determine the real position of the aircraft?
I'm only a retired controller, not a pilot, but I'll try to answer one or two of your points from personal experience.
Before VOR/DME became the 'standard' nav system, several other systems were tried, one being DECCA/Doppler. This was fitted to most of the BEA (British European Airways) jet fleet - I remember seeing it on Trident Mk 1s. I also remember when I was an assistant that in order to assist separating opposite direction aircraft, the pilot would be requested to 'fly DECCA left'. The DECCA/Doppler navigation system was put forward as the 'standard' worldwide but the American VOR system, shortly to be augmented by DME, was chosen instead. DECCA stations in those days (consisting of a master station and 3 slave stations), were already positioned around the world to provide navigation for shipping.
As to your questions:
The Tech log should have been read by the crew before accepting the aircraft so they SHOULD have known the VOR had been replaced.
Some companies required their crews to operate on one VOR and keep the other for backup whilst some required the in-use VOR on one and the next expected VOR to be dialled into the other.
I am unable to answer the third question.
The only backup to radar in those days was a pilot's report of position to a non-radar controller.
I've probably got some of the finer points wrong but it gives you some idea; maybe a BEA pilot from those days will see this and correct me.
Before VOR/DME became the 'standard' nav system, several other systems were tried, one being DECCA/Doppler. This was fitted to most of the BEA (British European Airways) jet fleet - I remember seeing it on Trident Mk 1s. I also remember when I was an assistant that in order to assist separating opposite direction aircraft, the pilot would be requested to 'fly DECCA left'. The DECCA/Doppler navigation system was put forward as the 'standard' worldwide but the American VOR system, shortly to be augmented by DME, was chosen instead. DECCA stations in those days (consisting of a master station and 3 slave stations), were already positioned around the world to provide navigation for shipping.
As to your questions:
The Tech log should have been read by the crew before accepting the aircraft so they SHOULD have known the VOR had been replaced.
Some companies required their crews to operate on one VOR and keep the other for backup whilst some required the in-use VOR on one and the next expected VOR to be dialled into the other.
I am unable to answer the third question.
The only backup to radar in those days was a pilot's report of position to a non-radar controller.
I've probably got some of the finer points wrong but it gives you some idea; maybe a BEA pilot from those days will see this and correct me.
I never worked for BEA but I did work for Dan-Air as a Licensed Radio Engineer and have seen more variants of Comet than most.
Decca and Doppler are two distinct navigation systems and not the same thing at all. Decca is/was a hyperbolic navigation system relying on ground stations, a Master and three slaves. Doppler is/was a self contained system with no external requirements.
The ex BEA 4bs were fitted with Decca as, in Dan-Air service thay had blanks where the Decometers and the moving map display were fitted. They did not have Doppler. In Dan-Air service they were conventional Dual VOR/ILS, Dual NDB aircraft with no other aids.
The Comet 4s did not have Doppler or Decca and were conventional Dual VOR/ILS, Dual NDB and Loran aircraft.
Some 4Cs were equipped like the 4s but with the addition of a dual Doppler system. Not all were so equipped.
I have never seen any Comet other than the BEA 4bs with Decca.
HTH.
Decca and Doppler are two distinct navigation systems and not the same thing at all. Decca is/was a hyperbolic navigation system relying on ground stations, a Master and three slaves. Doppler is/was a self contained system with no external requirements.
The ex BEA 4bs were fitted with Decca as, in Dan-Air service thay had blanks where the Decometers and the moving map display were fitted. They did not have Doppler. In Dan-Air service they were conventional Dual VOR/ILS, Dual NDB aircraft with no other aids.
The Comet 4s did not have Doppler or Decca and were conventional Dual VOR/ILS, Dual NDB and Loran aircraft.
Some 4Cs were equipped like the 4s but with the addition of a dual Doppler system. Not all were so equipped.
I have never seen any Comet other than the BEA 4bs with Decca.
HTH.
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Thank you all for your answers.
My questions are related with the report of the Dan Air Comet 4 G-APDN accident near Barcelona (1970). I became interested in this case, because from time to time, I go for a walk in the mountain, and sometimes a walk near the place of the accident. There is not so much information about it. Several months ago I find the report (it's on gov.uk), and I read it, several times because, obviously I wasn't able to understant anything. My questions are about things explained on the report.
The “doppler out of action (allowable)” and the “1 VOR set” which was replaced because of previous malfunctions are mentioned at the beginning of the report, and I wanted to understand a little bit what they are; just because in the “conclusion and propable causes” they said “they aircraft displacement to east could have come as a result of some defect of the aircraft equipment”. But they did not point specifically to any equipment.
I have another question.
They say the cause of the accident was a combination of “erroneous information regarding reporting points, together with the existence of a radar echo coinciding with the report from the aircraft of passing that reporting point” (an echo with characteristics similar to those which the Comet should produce in terms of direction and speed). But they did not point to any kind of explanation/hypohesis about what this false echo was. The report say the radar was working properly.
(Into the context of 1970)
What do you think about?
Is a false echo a common thing?
Any hipothesis?
My questions are related with the report of the Dan Air Comet 4 G-APDN accident near Barcelona (1970). I became interested in this case, because from time to time, I go for a walk in the mountain, and sometimes a walk near the place of the accident. There is not so much information about it. Several months ago I find the report (it's on gov.uk), and I read it, several times because, obviously I wasn't able to understant anything. My questions are about things explained on the report.
The “doppler out of action (allowable)” and the “1 VOR set” which was replaced because of previous malfunctions are mentioned at the beginning of the report, and I wanted to understand a little bit what they are; just because in the “conclusion and propable causes” they said “they aircraft displacement to east could have come as a result of some defect of the aircraft equipment”. But they did not point specifically to any equipment.
I have another question.
They say the cause of the accident was a combination of “erroneous information regarding reporting points, together with the existence of a radar echo coinciding with the report from the aircraft of passing that reporting point” (an echo with characteristics similar to those which the Comet should produce in terms of direction and speed). But they did not point to any kind of explanation/hypohesis about what this false echo was. The report say the radar was working properly.
(Into the context of 1970)
What do you think about?
Is a false echo a common thing?
Any hipothesis?
Identifying an aircraft by correlating a position report with the existence of a radar return at that reporting point is an accepted method when using primary only radar; I don't think the Spanish had SSR display s in those days.
I was on duty at West Drayton when the accident happened.
A 'spurious ' echo on a radar is not an uncommon occurence when using un-processed primary radar.
I was on duty at West Drayton when the accident happened.
A 'spurious ' echo on a radar is not an uncommon occurence when using un-processed primary radar.
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Thanks chevron.
Barcelona ACC/APP had a ASR-5 radar equipment. The report did not mention any secondary radar. After reading the report, I understand that rules laid down by ICAO for radar identification at that time, did not include an SSR equipment as a mandatory equipment. In the “Recomendations” chapter of the report, they say “the spanish autorithies have already made a suitable provision in this respect, so that identification can be properly checked by more than one method”.
You say you were on duty when the accident happened. Did West Drayton have a secondary surveillance radar at that time? What I mean is if an SSR was a common equipment by those times in other countries. It is well known that Spain, generally speaking, was backward Europe in terms of technology in those times, but I don't know the real situation regarding to air traffic control.
Barcelona ACC/APP had a ASR-5 radar equipment. The report did not mention any secondary radar. After reading the report, I understand that rules laid down by ICAO for radar identification at that time, did not include an SSR equipment as a mandatory equipment. In the “Recomendations” chapter of the report, they say “the spanish autorithies have already made a suitable provision in this respect, so that identification can be properly checked by more than one method”.
You say you were on duty when the accident happened. Did West Drayton have a secondary surveillance radar at that time? What I mean is if an SSR was a common equipment by those times in other countries. It is well known that Spain, generally speaking, was backward Europe in terms of technology in those times, but I don't know the real situation regarding to air traffic control.
Yes West Drayton had SSR at that time, but it wasn't in the form familiar to most people nowadays. There was no data block on the radar screen, just a 'slash' following the blip of the aircraft you were identifying, with another slash appearing for a short time in response to an instruction to 'squawk ident'.
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Thank you all again.
I've been looking for in some spanish press archives and I found that the first SSR equipments (for civil aviation) in Spain were installed in 1972. I found some old brochures from the early 60's (from outside of Spain, from BEA for example) saying that their aircrafts were fitted with new “transponder equipments”. This thing makes me think that in other european countries SSR equipments were installed maybe since the early 60's or late 50's. (?)
The aircraft's transponder equipment by those times was only linked with the SSR, or it had already another kind of functions?
I've been looking for in some spanish press archives and I found that the first SSR equipments (for civil aviation) in Spain were installed in 1972. I found some old brochures from the early 60's (from outside of Spain, from BEA for example) saying that their aircrafts were fitted with new “transponder equipments”. This thing makes me think that in other european countries SSR equipments were installed maybe since the early 60's or late 50's. (?)
The aircraft's transponder equipment by those times was only linked with the SSR, or it had already another kind of functions?
