Single v Twin
Thread Starter
Joined: Jun 2008
Posts: 1,413
Likes: 0
From: England & Scotland
Single v Twin
Interesting article
Questioning Single-Engine Helicopter Performance
Matt Callan
ICAO’s reasoning: if an engine failure occurs at any time during the flight, a single-engine aircraft will be forced to land. Governments that participate in ICAO are offered two choices. Either (1) restrict the operation of single-engine aircraft over congested areas (ICAO defines these as any used for residential, commercial, or recreational purposes, which ends up eliminating a lot of land, particularly in densely populated countries) or (2) implement their own performance standards for helicopter operations (which the United States, among others, has done). The result is that single-engine aircraft are being regulated out of the civil fleet in many of the 192 nations that are ICAO members.
In fact, there is no justifiable reason to portray single-*engine helicopters as being inherently more dangerous. Companies that work regularly in mountainous and high-terrain areas often use single-engine helicopters because of their superior performance under those conditions. And just like single-engine
helicopters, those with twin engines have only one tail rotor, one main rotor gear box, one tail rotor gearbox, and one tail rotor drive shaft. The failure of any one of these critical components means that aircraft is going down—regardless of the number of engines.
The sad truth is that the majority of helicopter mishaps result from pilots making judgment errors, losing control of the aircraft, and flying perfectly good machines into terrain. According to the US Helicopter Safety Team, the top three types of helicopter mishaps (loss of control, unintended flight in instrument meteorological conditions, and low-altitude operations) accounted for more than 50 percent of the helicopter fatalities (104), more than the remaining 15 types combined (96).
Accident data from other ICAO-participating states support the safety of single-engine helicopters. The Australian Transportation Safety Board classified accidents over a five-year period as either mechanical or operational. Of the 749 accidents recorded during the period, just over a quarter (197) were attributed to mechanical problems. In other words, close to 75 percent of those accidents were not mechanical (that is, pilot error).
Japan, a country with a relatively small land mass and numerous mountains, is an ICAO-participating state that employs over 300 single-engine helicopters. According to Japanese aviation records, there are presently 814 registered helicopters operating in the country, with a ratio of 42.1 percent single-engine and 57.9 percent twin. Over the last 20 years, the numbers of single*engine helicopters have decreased, but the country still has many single-engine helicopters that regularly fly over Japanese airspace.
According to statistics obtained from its Transport Safety Board, Japan has not experienced a single accident or incident caused by an engine failure in the last 10 years. Once again, pilot error is the leading cause of accidents or incidents—in singles and twins. Although mechanical issues did contribute to mishaps, they were caused by detachment of the tail rotor (immune from the number of engines) and a fire in the cargo compartment.
These mishap statistics tell the same story as those from the United States: the clear majority of helicopter accidents are caused by pilot error, not by system malfunction. Wouldn’t our attention, time, and money be better spent on training pilots instead of banning single*-engine helicopters?
Instead of focusing an inordinate amount of time, energy, and resources to paint single-engine helicopters as potential high-risk operations, ICAO and its member states should instead invest in improved pilot training, risk assessment and mitigation, and crew resource *management.
Questioning Single-Engine Helicopter Performance
Matt Callan
Let’s focus on what causes most accidents (hint: it’s not engine failures).
While the US helicopter industry enjoys relatively nonrestrictive single*engine regulations, the rest of the world is experiencing increasingly prescriptive standards and recommended practices issued by the International Civil Aviation Organization (ICAO) that are aimed directly at limiting the operation of single-engine helicopters.ICAO’s reasoning: if an engine failure occurs at any time during the flight, a single-engine aircraft will be forced to land. Governments that participate in ICAO are offered two choices. Either (1) restrict the operation of single-engine aircraft over congested areas (ICAO defines these as any used for residential, commercial, or recreational purposes, which ends up eliminating a lot of land, particularly in densely populated countries) or (2) implement their own performance standards for helicopter operations (which the United States, among others, has done). The result is that single-engine aircraft are being regulated out of the civil fleet in many of the 192 nations that are ICAO members.
In fact, there is no justifiable reason to portray single-*engine helicopters as being inherently more dangerous. Companies that work regularly in mountainous and high-terrain areas often use single-engine helicopters because of their superior performance under those conditions. And just like single-engine
helicopters, those with twin engines have only one tail rotor, one main rotor gear box, one tail rotor gearbox, and one tail rotor drive shaft. The failure of any one of these critical components means that aircraft is going down—regardless of the number of engines.
The sad truth is that the majority of helicopter mishaps result from pilots making judgment errors, losing control of the aircraft, and flying perfectly good machines into terrain. According to the US Helicopter Safety Team, the top three types of helicopter mishaps (loss of control, unintended flight in instrument meteorological conditions, and low-altitude operations) accounted for more than 50 percent of the helicopter fatalities (104), more than the remaining 15 types combined (96).
Accident data from other ICAO-participating states support the safety of single-engine helicopters. The Australian Transportation Safety Board classified accidents over a five-year period as either mechanical or operational. Of the 749 accidents recorded during the period, just over a quarter (197) were attributed to mechanical problems. In other words, close to 75 percent of those accidents were not mechanical (that is, pilot error).
Japan, a country with a relatively small land mass and numerous mountains, is an ICAO-participating state that employs over 300 single-engine helicopters. According to Japanese aviation records, there are presently 814 registered helicopters operating in the country, with a ratio of 42.1 percent single-engine and 57.9 percent twin. Over the last 20 years, the numbers of single*engine helicopters have decreased, but the country still has many single-engine helicopters that regularly fly over Japanese airspace.
According to statistics obtained from its Transport Safety Board, Japan has not experienced a single accident or incident caused by an engine failure in the last 10 years. Once again, pilot error is the leading cause of accidents or incidents—in singles and twins. Although mechanical issues did contribute to mishaps, they were caused by detachment of the tail rotor (immune from the number of engines) and a fire in the cargo compartment.
These mishap statistics tell the same story as those from the United States: the clear majority of helicopter accidents are caused by pilot error, not by system malfunction. Wouldn’t our attention, time, and money be better spent on training pilots instead of banning single*-engine helicopters?
Instead of focusing an inordinate amount of time, energy, and resources to paint single-engine helicopters as potential high-risk operations, ICAO and its member states should instead invest in improved pilot training, risk assessment and mitigation, and crew resource *management.
Last edited by Senior Pilot; 4th June 2020 at 07:05. Reason: Add quote so Rotorheads know what your post is about!
Joined: Mar 2004
Posts: 273
Likes: 0
From: hayling island
Are Twins safer
Basically we know twins are no safer than singles, but what you really need is a single and a twin doing exactly the same job in the same conditions to prove the case.
Authorities never compare like for like, most singles do all the dangerous work, initial training, load lifting, low time pilot hour building etc so the accident rate is bound to be skewed.
Only once you have experience do they let you fly twins, so that also changes the stats in favour of the twins.
That's my pennies worth, have a nice debate
Authorities never compare like for like, most singles do all the dangerous work, initial training, load lifting, low time pilot hour building etc so the accident rate is bound to be skewed.
Only once you have experience do they let you fly twins, so that also changes the stats in favour of the twins.
That's my pennies worth, have a nice debate
Joined: Sep 2007
Posts: 744
Likes: 5
From: london
Basically we know twins are no safer than singles, but what you really need is a single and a twin doing exactly the same job in the same conditions to prove the case.
) as he needed his pension and didnt want to risk the issues that might arise should an incident occur.I thought this old argument had been done to death, resurrected and then murdered again.....
Joined: Jul 2011
Posts: 187
Likes: 37
From: N/A
Funny thing is that those missions where a second engine could really save the day during an engine failure are mostly done by single engines: aerial work. Money and not safety talks here.
Statistics are famous for the fact that they can be twisted the way the users wants.
If I am doing a powerline inspection in, let’s say a H125 and the engine quits I am dead... if I do the same in a H135 I would simply fly away, RTB and have a beer. That engines generally fail very rarely, THAT is a good thing. That OLD twins are actually a “handful” when an engine fails is also true... however modern FADEC regulated twins with power to spare once in OEI definitely have their benefits.
Also would not enjoy a forced autorotation in IFR with the clouddeck at 300ft in a Single whereas in a twin the only thing that really would happen is that your endurance increases!
Statistics are famous for the fact that they can be twisted the way the users wants.
If I am doing a powerline inspection in, let’s say a H125 and the engine quits I am dead... if I do the same in a H135 I would simply fly away, RTB and have a beer. That engines generally fail very rarely, THAT is a good thing. That OLD twins are actually a “handful” when an engine fails is also true... however modern FADEC regulated twins with power to spare once in OEI definitely have their benefits.
Also would not enjoy a forced autorotation in IFR with the clouddeck at 300ft in a Single whereas in a twin the only thing that really would happen is that your endurance increases!
Joined: Apr 2007
Posts: 382
Likes: 15
From: Out there
I'd much rather fly a single squirrel than a twin squirrel any day. Oh, and I fly both every week, just to validate that statement! I actually fly 135 and 412 too and I'd take the single squirrel first out of any of them, depending on the task.
Joined: Apr 2003
Posts: 481
Likes: 58
From: USA
Don’t forget the stats are baked. They don’t take into account engines that were shut down as a precaution to an impending engine failure (oil line coming off etc).
I know I’ve had to shut down an engine at least 3 times in flight and come on home on the remaining good engine.
What I’m getting at the stats don’t really reflect the amount of aircraft that would have had an engine failure, but isn’t really recorded (apart from maybe an internal company report or NASA report etc depending on country) because it was shut down and flown back safely on remaining engine.
That being said I still have zero problems personally flying a single.
I know I’ve had to shut down an engine at least 3 times in flight and come on home on the remaining good engine.
What I’m getting at the stats don’t really reflect the amount of aircraft that would have had an engine failure, but isn’t really recorded (apart from maybe an internal company report or NASA report etc depending on country) because it was shut down and flown back safely on remaining engine.
That being said I still have zero problems personally flying a single.
Joined: Sep 2002
Aviation Qualifications: CPL
Posts: 4,721
Likes: 636
From: Great South East, tired and retired
Twins are flown in tasks that singles are not suited for - carrying VIP in IMC is one example, but there is a considerable number of twins which fall from the sky because of mistakes with the fuel system, or just bumbling into a hill when IMC and not supposed to be.
I have about 13,000 hrs in singles and 2000 hrs in twins, happy to fly either. But at night I prefer the extra weight and comfort of the second engine. It makes soothing sounds.
I have about 13,000 hrs in singles and 2000 hrs in twins, happy to fly either. But at night I prefer the extra weight and comfort of the second engine. It makes soothing sounds.
Joined: Mar 2005
Aviation Qualifications: Military
Posts: 6,562
Likes: 952
From: Aus
What I’m getting at the stats don’t really reflect the amount of aircraft that would have had an engine failure, but isn’t really recorded (apart from maybe an internal company report or NASA report etc depending on country) because it was shut down and flown back safely on remaining engine
Joined: Jul 2005
Posts: 136
Likes: 0
From: suffolk uk
I had a single engine failure and a twin engine "voluntary" shut down in my 40+ year career. Clearly I survived both. The thing is that flown correctly with the possibility of an engine failure always in mind singles are no less safe than twins.
"Just a pilot"
Joined: May 2001
Posts: 633
Likes: 8
From: Jefferson GA USA
Twins are flown in tasks that singles are not suited for - carrying VIP in IMC is one example, but there is a considerable number of twins which fall from the sky because of mistakes with the fuel system, or just bumbling into a hill when IMC and not supposed to be.
I have about 13,000 hrs in singles and 2000 hrs in twins, happy to fly either. But at night I prefer the extra weight and comfort of the second engine. It makes soothing sounds.
I have about 13,000 hrs in singles and 2000 hrs in twins, happy to fly either. But at night I prefer the extra weight and comfort of the second engine. It makes soothing sounds.
I've flown for operators who regarded the second engine as the ability to safely fly in reduced weather. No better IFR equipment, just a second engine.
Below the Glidepath - not correcting
Joined: Jun 2005
Posts: 1,886
Likes: 97
From: U.S.A.
Twins are more complicated and there's no way around the complexity. Integrating two engines, two generators, etc., will always present more opportunity for mistake. Mistakes cause crashes. High side/low side fuel control failures, for instance... or generator failures- at least in the old designs I flew- what's on which bus? What will you lose?
I've flown for operators who regarded the second engine as the ability to safely fly in reduced weather. No better IFR equipment, just a second engine.
I've flown for operators who regarded the second engine as the ability to safely fly in reduced weather. No better IFR equipment, just a second engine.
There is no right answer to this perennial question, it's about risk, hazards and mitigation, and every operation will be different. Whatever works for you is the answer, or actually, whatever works for the person who paid for the airframe.
Joined: Aug 2000
Posts: 2,111
Likes: 118
well I seem to remember flying IFR in a 341 in UK, but was in the military
I am led to believe that nearly 90% of heli accidents are pilot error
The problem is we will never really know as there are too many variables and like my accountant he can make figures read what ever he wants.
I am led to believe that nearly 90% of heli accidents are pilot error
The problem is we will never really know as there are too many variables and like my accountant he can make figures read what ever he wants.
