Category A Takeoff: Background
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I first landed on the IPC roof in London in January 1975 in a Bo105D - can't remember any formal Cat A being in force for that type at that time. In fact in wasn't until four years later in June 1979 that I flew some rooftop take off single engine failure assessment flights on a 105DB with George Locke (ex-CO D Squadron at Boscombe Down) who was MD of Helicopter Marketing, the MBB sales agents in the UK at that time.
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Well done Tees! 
Flight International, 2nd November, 1985
Mike Barrett, McAlpine Helicopter's chief pilot, sees the UK Civil Aviation Authority attitude to helicopter operations as enlightened, compared with the restrictive regulations in other European countries.
After an initial period of reservation, the CAA has been practical and co-operative in establishing criteria for the newspaper operation. McAlpine is confident that city rooftop pads have significant advantages over ground-level pads for safety, environmental, and utility reasons. The elevated platform allows improved clearance of surrounding obstructions, particularly in the event of engine failure during approach or departure. It ensures low noise disturbance (amazingly, this operation has received almost no noise complaints from local residents in more than three years).
Rooftop platforms may come in handy for rapid fire and medical evacuation. Few buildings in London's crowded skyline are stressed to take the weight of helicopter. Many roofs are cluttered with air-conditioning vents, railings, and other impedimenta which would make even an emergency landing a hazardous undertaking.
Perhaps designers of city tower blocks should give thought to the beneficial role that the helicopter can play as a public service vehicle. This is one of the fastest growing areas of helicopter usage in the USA today.
CAA regulations stipulate that the diameter of an elevated pad should be at least 2 times that of the helicopter's rotor—some 88ft in the case of the Twin Squirrel. In addition, the pilot must be able to lift-off from the pad to a Critical Decision Point (CDP) 90ft above the pad elevation, lose one engine, and either land safely clear of the building or continue with a single-engined departure without sinking to less than 35ft above pad elevation.
The square International Press Centre roof measures 46ft x 46ft, and the Twin Squirrel, with its 35ft rotor diameter, can meet neither requirement with a normal lift-off technique. McAlpine Helicopters has developed special procedures to meet the CAA criteria. These have been demonstrated to, and approved by, the CAA, and involve a lift-off to 15ft above the pad, followed by a climb in backward flight, keeping the pad in sight through the pilot's lower right-hand windshield. This reverse climb is continued to the 90ft CDP.
Single-engine safety is vital
In the event of an engine failure below this point, the pilot uses the departure pad as his emergency landing area. Should failure occur after CDP, a transition into descending forward flight is made, maintaining the minimum 35ft margin above roof elevation while accelerating to the take-off safety speed (Vtoss) of 40kt. Under IFR conditions the pilot must fly level, accelerating further to his best singleengined climb speed of 55kt (Vy), before starting his en-route climb. Under VFR, 40kt will be maintained in the climb until 550ft above departure elevation, before acceleration to 55kt.
Similar criteria apply for approach and landing, with a Landing Decision Point (LDP) 90ft above pad elevation. Engine failure above LDP entails a missed approach procedure, similar to the departure profile. Below LDP power loss entails landing on to the roof.
Before landing on the IPC, pilots take an engine condition reading to ensure full engine performance before starting an approach, wind 8mb off the London QNH (equal to the 240ft height of the helipad building), and then make an approach into wind (using local chimney smoke, or the flags on the Houses of Parliament two miles away) to land on the nearest into wind diagonal line across the roof.
This ensures the maximum landing dispersion distance, which allows leeway for the pilot's fore/aft touchdown error.
To the passenger the landing appears dramatic and, indeed, there is little room for error. Despite this, McAlpine research and development pilot Geoffrey Holder makes the technique look easy. He has played a major part in developing the rooftop techniques to the standards required by the CAA. Up to three passengers can be carried from the roof, together with the plates. In fact, there needs to be at least one passenger, in the copilot's seat, to prevent an aft e.g. position allowing the tail boom to strike the edge of the building.
After an initial period of reservation, the CAA has been practical and co-operative in establishing criteria for the newspaper operation. McAlpine is confident that city rooftop pads have significant advantages over ground-level pads for safety, environmental, and utility reasons. The elevated platform allows improved clearance of surrounding obstructions, particularly in the event of engine failure during approach or departure. It ensures low noise disturbance (amazingly, this operation has received almost no noise complaints from local residents in more than three years).
Rooftop platforms may come in handy for rapid fire and medical evacuation. Few buildings in London's crowded skyline are stressed to take the weight of helicopter. Many roofs are cluttered with air-conditioning vents, railings, and other impedimenta which would make even an emergency landing a hazardous undertaking.
Perhaps designers of city tower blocks should give thought to the beneficial role that the helicopter can play as a public service vehicle. This is one of the fastest growing areas of helicopter usage in the USA today.
CAA regulations stipulate that the diameter of an elevated pad should be at least 2 times that of the helicopter's rotor—some 88ft in the case of the Twin Squirrel. In addition, the pilot must be able to lift-off from the pad to a Critical Decision Point (CDP) 90ft above the pad elevation, lose one engine, and either land safely clear of the building or continue with a single-engined departure without sinking to less than 35ft above pad elevation.
The square International Press Centre roof measures 46ft x 46ft, and the Twin Squirrel, with its 35ft rotor diameter, can meet neither requirement with a normal lift-off technique. McAlpine Helicopters has developed special procedures to meet the CAA criteria. These have been demonstrated to, and approved by, the CAA, and involve a lift-off to 15ft above the pad, followed by a climb in backward flight, keeping the pad in sight through the pilot's lower right-hand windshield. This reverse climb is continued to the 90ft CDP.
Single-engine safety is vital
In the event of an engine failure below this point, the pilot uses the departure pad as his emergency landing area. Should failure occur after CDP, a transition into descending forward flight is made, maintaining the minimum 35ft margin above roof elevation while accelerating to the take-off safety speed (Vtoss) of 40kt. Under IFR conditions the pilot must fly level, accelerating further to his best singleengined climb speed of 55kt (Vy), before starting his en-route climb. Under VFR, 40kt will be maintained in the climb until 550ft above departure elevation, before acceleration to 55kt.
Similar criteria apply for approach and landing, with a Landing Decision Point (LDP) 90ft above pad elevation. Engine failure above LDP entails a missed approach procedure, similar to the departure profile. Below LDP power loss entails landing on to the roof.
Before landing on the IPC, pilots take an engine condition reading to ensure full engine performance before starting an approach, wind 8mb off the London QNH (equal to the 240ft height of the helipad building), and then make an approach into wind (using local chimney smoke, or the flags on the Houses of Parliament two miles away) to land on the nearest into wind diagonal line across the roof.
This ensures the maximum landing dispersion distance, which allows leeway for the pilot's fore/aft touchdown error.
To the passenger the landing appears dramatic and, indeed, there is little room for error. Despite this, McAlpine research and development pilot Geoffrey Holder makes the technique look easy. He has played a major part in developing the rooftop techniques to the standards required by the CAA. Up to three passengers can be carried from the roof, together with the plates. In fact, there needs to be at least one passenger, in the copilot's seat, to prevent an aft e.g. position allowing the tail boom to strike the edge of the building.
Avoid imitations
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The rearwards departure from a helipad is normal for a number of other helicopters (I do at least one almost every working day).
The FAA had approved Cat A for the Bell 212 in 1972, so any development would have been well in place before that. The attached scans indicate both the approval date of the Cat A Supplement (18th August 1972) and the profile:
I think it somewhat cheeky for the Flight article to infer that McAlpine had developed this technique some 13 years after this Bell 212 example, even allowing for journalistic license. I'm sure that there would be other examples prior to the 212, certainly the S61.
John Boy.....the FAA lead the CAA in something as sophisticated as this.....really?
We all know that the Yanks could not possibly understand the finer points of helicopter flying!
We all know that the Yanks could not possibly understand the finer points of helicopter flying!
Belgrano House....sounds like a deep water Reef!
Sadly....the Brits were quite late to the party....and have had great success imitating more progressive nations re rotary wing flight.
Seems the Russians and Germans led the way.
A History of Helicopter Flight
Sadly....the Brits were quite late to the party....and have had great success imitating more progressive nations re rotary wing flight.
Seems the Russians and Germans led the way.
A History of Helicopter Flight
Avoid imitations
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A fairly simple question but ... as so often happens here, it quickly becomes another tree against which the old dogs rush to cock their legs. 
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dubious maths
seems like dubious maths to expose the aircaft (and it's other sytems) to such a prolonged vunerable state for the theoretical upside of being able to crash gently back on the pad if it's the engine that fails in this time frame.
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John: Thanks for the info on the 212. Would be interesting to read a more detailed instruction of the recommended procedure.
Perhaps then it was one of the Bell test pilots who developed the original CAT A takeoff?
AnFI: I believe the rationale was that even if it takes longer .. the craft follows a profile in which there is always an 'option'. In the case of McAlpines and the UK CAA (above) and given the TwinEcureuil's power (or rather lack thereof) combined with the departure area being over central London; it seems as if this was the only means of mitigating the risk of recovery from a loss of power immediately following takeoff. But .. I appreciate your point.
I believe 'low level, gain speed, then climb' departures are still used from airports (see below):
But CAT A (reversing style) are carried-out from helipads (from 02:05):
Perhaps then it was one of the Bell test pilots who developed the original CAT A takeoff?
I believe 'low level, gain speed, then climb' departures are still used from airports (see below):
But CAT A (reversing style) are carried-out from helipads (from 02:05):
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Just browsed by this thread and wanted to pass on my thoughts:
The first category a helicopter was the S61, which was certified in the early 1960s. It was a CAM 7 certified helicopter, the predecessor to FAR Part 29, and so it was certified to airline transport requirements. This meant that the FAA had to synthesize requirements that were similar to the Part 25 airplane airline transport requirements. Part 25 requirements had engine failure on takeoff, rotation speeds, accelerate stop distances, and takeoff distances. All were specified using careful flight test procedures.
The Category A procedures used for the S61 family included a runway procedure and elevated heliport procedures. The elevated heliport procedures were used for the very first transport operations between the Pan Am building in downtown New York and the New York world's fair Pavilion in Flushing Meadows, New York. The test pilots who performed these procedures told tales of flying over 1000 takeoffs and landings as part of the certification effort. I met Jim Plackis the other day, he was the FAA test pilot on these operations.
The S61 was the precursor to all these Category A operations that are now standard for part 29 helicopters.
The first category a helicopter was the S61, which was certified in the early 1960s. It was a CAM 7 certified helicopter, the predecessor to FAR Part 29, and so it was certified to airline transport requirements. This meant that the FAA had to synthesize requirements that were similar to the Part 25 airplane airline transport requirements. Part 25 requirements had engine failure on takeoff, rotation speeds, accelerate stop distances, and takeoff distances. All were specified using careful flight test procedures.
The Category A procedures used for the S61 family included a runway procedure and elevated heliport procedures. The elevated heliport procedures were used for the very first transport operations between the Pan Am building in downtown New York and the New York world's fair Pavilion in Flushing Meadows, New York. The test pilots who performed these procedures told tales of flying over 1000 takeoffs and landings as part of the certification effort. I met Jim Plackis the other day, he was the FAA test pilot on these operations.
The S61 was the precursor to all these Category A operations that are now standard for part 29 helicopters.
Thread Starter
Nick thank you.
Just to confirm then, for the record as it were, that what is now the Helicopter Category A departure (rooftop/helipad style) finds its origins in the work of Sikorsky's test pilots (including Jim Plackis) in the 1960's flying the S61?
Just to confirm then, for the record as it were, that what is now the Helicopter Category A departure (rooftop/helipad style) finds its origins in the work of Sikorsky's test pilots (including Jim Plackis) in the 1960's flying the S61?
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Savoia, To my knowledge, the S61 was the first Airline Transport helo, and had the first Cat A procedural approval, in either 1961 or 62. It was quickly (within a few months!) followed by a vertol machine, I believe the civil Vertol 107.
Here is a link to the historic archived TCDS, dated 11/1/1961, and including Cat A procedures: Type Certificate Data Sheet 1H15
The Bell 212 Cat A was dated 6/30/1971: Type Certificate Data Sheet H4SW
The V-107 1/26/1962:Type Certificate Data Sheet 1H16
Here is a link to the historic archived TCDS, dated 11/1/1961, and including Cat A procedures: Type Certificate Data Sheet 1H15
The Bell 212 Cat A was dated 6/30/1971: Type Certificate Data Sheet H4SW
The V-107 1/26/1962:Type Certificate Data Sheet 1H16
Last edited by NickLappos; 30th Nov 2013 at 19:57.
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Any successful cases?
Savoia - yes you are right that is the 'rationale'
There must have been some successful outcomes of an engine failing at the higher end of the back-up phase, say 50ft of say 90ft.
Are there any examples known here by ppruners? How did they fare?
I heard of an engine failure on climb out in a single in 1974, the outcome was successful.
I love the history - you can feel the optimism!
Roof top restaurant heliport - marvelous!
Of course back then engines weren't so reliable and they were running singles almost flatout to takeoff, making it even more attractive to have 2 engines.
There must have been some successful outcomes of an engine failing at the higher end of the back-up phase, say 50ft of say 90ft.
Are there any examples known here by ppruners? How did they fare?
I heard of an engine failure on climb out in a single in 1974, the outcome was successful.
I love the history - you can feel the optimism!
Roof top restaurant heliport - marvelous!
Of course back then engines weren't so reliable and they were running singles almost flatout to takeoff, making it even more attractive to have 2 engines.
John,
Nick did not win the Barnes Wallis Award because of his mere good looks and charm...(sounds of coughing heard)!
Nick did not win the Barnes Wallis Award because of his mere good looks and charm...(sounds of coughing heard)!
Nick,
Nice to see you posting again: but the photo of the NY World Fair reminded me that I visited it (the World Fair) in 1965, and I wasn't aware of the helipad until your post
How time flies when you're having fun
Nice to see you posting again: but the photo of the NY World Fair reminded me that I visited it (the World Fair) in 1965, and I wasn't aware of the helipad until your post
How time flies when you're having fun