Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Single v Twin

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Single v Twin

Old 4th Jun 2020, 06:39
  #1 (permalink)  
Thread Starter
 
Join Date: Jun 2008
Location: England & Scotland
Age: 60
Posts: 1,369
Single v Twin

Interesting article

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 Jun 2020 at 07:05. Reason: Add quote so Rotorheads know what your post is about!
John R81 is offline  
Old 4th Jun 2020, 08:07
  #2 (permalink)  
 
Join Date: Aug 2000
Posts: 1,667
well this will be a never ending debate ! I have almost always flown singles and am still here 9000 hours later
Hughes500 is offline  
Old 4th Jun 2020, 08:56
  #3 (permalink)  
 
Join Date: Mar 2004
Location: hayling island
Posts: 257
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
timprice is offline  
Old 4th Jun 2020, 12:55
  #4 (permalink)  

 
Join Date: Nov 2000
Location: White Waltham, Prestwick & Calgary
Age: 68
Posts: 3,818
I've always taught that a twin is only "safer" when one engine fails.
paco is offline  
Old 4th Jun 2020, 13:16
  #5 (permalink)  
 
Join Date: Sep 2007
Location: london
Posts: 705
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.
No, what you need is someone at the CAA (insert name of your regulator here) willing to sign off. I recall discussing single engine IFR with my FOI in the 1980s who agreed there was no reason not to allow, but then pointed out he wouldnt sign it off (on the theoretical basis that he could ) 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.....
homonculus is offline  
Old 4th Jun 2020, 17:33
  #6 (permalink)  
 
Join Date: Jul 2011
Location: N/A
Age: 43
Posts: 35
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, letís 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 ďhandfulĒ 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!
casper64 is offline  
Old 5th Jun 2020, 02:55
  #7 (permalink)  
 
Join Date: Apr 2007
Location: Out there
Posts: 282
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.
Evil Twin is offline  
Old 5th Jun 2020, 04:07
  #8 (permalink)  
 
Join Date: Apr 2003
Location: USA
Posts: 105
Donít forget the stats are baked. They donít take into account engines that were shut down as a precaution to an impending engine failure (oil line coming off etc).

I know Iíve had to shut down an engine at least 3 times in flight and come on home on the remaining good engine.

What Iím getting at the stats donít really reflect the amount of aircraft that would have had an engine failure, but isnít 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.
havick is online now  
Old 5th Jun 2020, 06:38
  #9 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 2,821
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.
Ascend Charlie is offline  
Old 5th Jun 2020, 07:12
  #10 (permalink)  
 
Join Date: Mar 2005
Location: N/A
Posts: 3,269
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
Had so many of those flying twins I lost count, never a problem on singles other than a clogged fuel filter on one occasion, the vast majority of single and twin time was over water. Hate Turbomeca, two engines that self destructed.
megan is offline  
Old 21st Jun 2020, 09:15
  #11 (permalink)  
 
Join Date: Jul 2005
Location: suffolk uk
Posts: 135
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.
uncle ian is offline  
Old 21st Jun 2020, 13:08
  #12 (permalink)  
 
Join Date: May 2002
Location: Wanaka, NZ
Posts: 2,199
Originally Posted by megan View Post
..Hate Turbomeca, two engines that self destructed.
Yeah, but on both occasions you had a spare Turbomeca that saved the day.
gulliBell is online now  
Old 21st Jun 2020, 14:52
  #13 (permalink)  
"Just a pilot"
 
Join Date: May 2001
Location: Jefferson GA USA
Age: 70
Posts: 600
Originally Posted by Ascend Charlie View Post
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.
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.
Devil 49 is offline  
Old 21st Jun 2020, 16:16
  #14 (permalink)  
 
Join Date: Sep 2011
Location: USA
Age: 51
Posts: 274
Originally Posted by Ascend Charlie View Post

and 2000 hrs in twins,
That all? I thought you were an expert !
Sir Korsky is offline  
Old 21st Jun 2020, 17:22
  #15 (permalink)  
Below the Glidepath - not correcting
 
Join Date: Jun 2005
Location: U.S.A.
Posts: 1,667
Originally Posted by Devil 49 View Post
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.
Devil, this is the factor most people either miss or choose to ignore. The added complexity of transmission drives, clutches, freewheels etc. in conjunction with electrical and hydraulic power generation all add multiple failure paths. In a complex system, the reliability is based entirely on the most unreliable component, not the most reliable component, which is usually the engine. There are plenty of circumstances where a twin is a safer option, but not necessarily a more reliable option. I've always felt more comfortable operating over water with two engines rather than one, but my pucker factor was then focused on multiple systems rather than a single engine tacho.

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.
Two's in is offline  
Old 21st Jun 2020, 19:05
  #16 (permalink)  
 
Join Date: Aug 2019
Location: PA
Posts: 10
I thought this debate existed only in piston FW world
kansarasc is online now  
Old 21st Jun 2020, 20:09
  #17 (permalink)  
 
Join Date: Jun 2020
Location: UK
Posts: 1
Like some have said a lot of the jobs where using a twin would improve safety dramatically are mostly done by singles, I imagine mainly down to cost
TatawaKecil is online now  
Old 21st Jun 2020, 20:17
  #18 (permalink)  
 
Join Date: Jun 2016
Location: Brantisvogan
Posts: 634
Originally Posted by kansarasc View Post
I thought this debate existed only in piston FW world
aviation is just one mass debate after another
Bell_ringer is offline  
Old 22nd Jun 2020, 07:04
  #19 (permalink)  
 
Join Date: Aug 2000
Posts: 1,667
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.
Hughes500 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.