Oceanic Long Haul - 2 or 4?
Join Date: Sep 1999
Location: The Deep South (Sussex)
Posts: 783
Likes: 0
Received 0 Likes
on
0 Posts
A bit more history:
When pilots were first contemplating crossing the English Channel, the preference was always for single engined airplanes as there was only 50% of suffering an engine failure. Single engined performance has improved a tad since then.
There used to be the story of the Pan Am Captain, who, having lost one over the Atlantic eventually arrived in Keflavik. He walked into ops and was greeted with the words:
"Are you the Pan Am A300 Captain"
To which he replied:
"Used to be Son, used to be..."
I understand that he bid back on to the 727 on his return to base.
Wasn't the last ditching of a passenger plane in the Atlantic (excluding ferry flights) the Flying Tigers Connie on a Military Charter in the late fifties?
When pilots were first contemplating crossing the English Channel, the preference was always for single engined airplanes as there was only 50% of suffering an engine failure. Single engined performance has improved a tad since then.
There used to be the story of the Pan Am Captain, who, having lost one over the Atlantic eventually arrived in Keflavik. He walked into ops and was greeted with the words:
"Are you the Pan Am A300 Captain"
To which he replied:
"Used to be Son, used to be..."
I understand that he bid back on to the 727 on his return to base.
Wasn't the last ditching of a passenger plane in the Atlantic (excluding ferry flights) the Flying Tigers Connie on a Military Charter in the late fifties?
PPRuNe Supporter
Join Date: Mar 2000
Location: Devon, UK
Posts: 194
Likes: 0
Received 0 Likes
on
0 Posts
The ARAC ETOPS working group applied a similar logic when analysing engine reliability requirements for new Extended Operations regulations (to be known as ETOPS to avoid confusion !?!). ARAC decided that in the event of two engines failing a four engined aircraft requires higher engine reliability than a three engined aircraft as it has twice as many engines left which can fail, and that a further engine failure on a quad (ie 1 engine remaining ) is just as likely to result in the aircraft not being able to land as would be the case in a 3 engined aircraft with all three engines failed.
ARAC ETOPS working group was obviously concerned with operations at great distance from a diversion aerodrome. My question is, would a quad with only one engine operating be able to maintain any altitude (no matter how low) or not?
ARAC ETOPS working group was obviously concerned with operations at great distance from a diversion aerodrome. My question is, would a quad with only one engine operating be able to maintain any altitude (no matter how low) or not?
Join Date: Apr 2003
Location: UK
Posts: 176
Likes: 0
Received 0 Likes
on
0 Posts
I have worked around brand new aircraft that have had an engine change directly after delivery for the very reason of staggered maintenance. In other words two different houred engines, this should answer the question posted previously about something coming from the factory with two potentially flawed engines.
The rules for maintenance on etops aircraft are very strict with regards to staggered maintenance and duplicate inspections etc. I have to say if i where driving the things i would be far more worried of a fire on board than an engine shutdown.
Finally out of all the shutdowns how many are a precaution rather than a neccesity, and how many of you would try and resart one if you suspect problems with the one remaining??
The rules for maintenance on etops aircraft are very strict with regards to staggered maintenance and duplicate inspections etc. I have to say if i where driving the things i would be far more worried of a fire on board than an engine shutdown.
Finally out of all the shutdowns how many are a precaution rather than a neccesity, and how many of you would try and resart one if you suspect problems with the one remaining??
Thread Starter
Join Date: Mar 2000
Location: Arizona USA
Posts: 8,571
Likes: 0
Received 0 Likes
on
0 Posts
Tallbloke,
Dunno about more modern types, but the B707-320B (advanced) certainly could at training weights only.
This was in the course at PanAmerican long ago, and I personally did so in the actual aircraft...number 3 operating at MCT, others at idle thrust.
The altitude was 4000msl. IAS 'round about 230, as I recall, rudder boost ON, of course.
Dunno about more modern types, but the B707-320B (advanced) certainly could at training weights only.
This was in the course at PanAmerican long ago, and I personally did so in the actual aircraft...number 3 operating at MCT, others at idle thrust.
The altitude was 4000msl. IAS 'round about 230, as I recall, rudder boost ON, of course.
Join Date: Dec 2002
Location: Wood's Hole (N4131.0 W07041.5)
Posts: 92
Likes: 0
Received 0 Likes
on
0 Posts
Okay, I seem to remember a conversation with a BAe design engineer who worked on the 146 program. He told me that the reason they went with 4 engines was that there wasn't a stage 3 engine developed with the thrust requirement for the wing pylon design, etc. That left them with the AVRO from (I think) the Bradley Fighting vehicle, or some other type of CAV eqpt.
As for the preferred number of engines on an aircraft, the simple rule is: count all the engines, divide it by 2 and the result MUST be a positive interger GREATER than 1. The MD11 meets that immediate requirement.
I understand that Boeing closed the LBA MD11 line down only because it was SERIOUS competition with its 757/767 line. Pity really - go and try to buy a 2nd hand MD11 today; theyr'e not around.
As for the preferred number of engines on an aircraft, the simple rule is: count all the engines, divide it by 2 and the result MUST be a positive interger GREATER than 1. The MD11 meets that immediate requirement.
I understand that Boeing closed the LBA MD11 line down only because it was SERIOUS competition with its 757/767 line. Pity really - go and try to buy a 2nd hand MD11 today; theyr'e not around.
Join Date: Oct 2003
Location: Canada
Posts: 1,852
Likes: 0
Received 0 Likes
on
0 Posts
I understand that Boeing closed the LBA MD11 line down only because it was SERIOUS competition with its 757/767 line
Join Date: Oct 2000
Posts: 74
Likes: 0
Received 0 Likes
on
0 Posts
Why all the fuss about twin engine jets flying over long stretches of water? They've been around for quite some time and proved themselves to be both safe and reliable.
Now if we really want to improve safety how about gettig rid of those REALLY dangerous bits of kit on aircraft.......flightdeck crew! All the reports I read seem to suggest they are the prime cause of accidents
Now if we really want to improve safety how about gettig rid of those REALLY dangerous bits of kit on aircraft.......flightdeck crew! All the reports I read seem to suggest they are the prime cause of accidents
With tongue in cheek, so many MD-11s (DC-10 was Death Cruiser, MD-11 More Death) having crashed, 'tis a wonder any are available. But, then again, every operator of them, save FedEx, is selling off their fleets. Except for those on US Mil contracts. And FedEx writes one off with frightening regularity.
Always wondred why, after the USAF bought 60 DC-10s, they started falling to earth like leaves in fall. The AF wrote off at least one in a ground fire.
But, this is MDD bashing.
GF
Always wondred why, after the USAF bought 60 DC-10s, they started falling to earth like leaves in fall. The AF wrote off at least one in a ground fire.
But, this is MDD bashing.
GF
Join Date: Mar 1999
Location: Ashbourne Co Meath Ireland
Age: 73
Posts: 470
Likes: 0
Received 0 Likes
on
0 Posts
For what it's worth, the comment I have heard from several people is that the MD 11 is not good in strong cross winds, due to all that weight at the back, and the smaller rudder size as a result of the 3rd engine in the middle.
Certainly it was a factor in the one that ran off the runway here in Dublin a while ago.
Certainly it was a factor in the one that ran off the runway here in Dublin a while ago.
Join Date: Jun 2004
Location: Australia
Posts: 1,843
Likes: 0
Received 0 Likes
on
0 Posts
I see that this topic has been idle for a while, it's time to re-awaken it from a new perspective. I've also done my share of iceberg counting across the North Atlantic and North Pacific, and am on intimate terms with the emptiness of the Indian ocean.
The fore-going discussions seem to relate to the .01% of the time that a modern jet aircraft suffers single or multiple engine failure. I prefer to address here the 99.99% of occasions that I DON'T lose an engine on a particular flight. (The statistics are far better than this, I'm erring on the conservative side).
Accepting that Takeoff at performance limited weight is probably the most critical of all times to suffer engine failure, the 2, 3, and 4 engined aircraft all meet APPROXIMATELY the same performance criteria with 1 engine inoperative (the 3 and 4 engined aircraft do it slightly better, but only slightly. If obstacle limited, they're identical). In short, the 2 engined aricraft achieves minimum performance on 50% of available thrust, the 3 engined on 67% of available thrust, and the 4 engined on 75% of that available. That ends the discussion on the .01% of flights that an engine fails.
If we look at the 99.99% of the time that an engine DOES NOT fail, and restore the thrust lost in the 'minimum performance' discussion, the 2 engine aircraft operates at a 100% surplus of that required, the 3 holer with a 50% surplus, whilst the 4 engined cow waddles about with a mere 33% margin of excess thrust above minimum.
Given that wind shear, terrain avoidance and other 'balls to the wall thrust' situations claim infinetly more lives and hulls than dead-stick ditchings, I'll stick to the aircraft with the greatest thrust reserve to save my neck in these situations, i.e. the modern 2 engined jet transport. (I have to use the word 'infinetly' here because dividing by zero yields infinity).
Yep, I still have some residual propaganda from a 'past life' on 3 and 4 holers whilst I idly count icebergs from my B777 perch.
The fore-going discussions seem to relate to the .01% of the time that a modern jet aircraft suffers single or multiple engine failure. I prefer to address here the 99.99% of occasions that I DON'T lose an engine on a particular flight. (The statistics are far better than this, I'm erring on the conservative side).
Accepting that Takeoff at performance limited weight is probably the most critical of all times to suffer engine failure, the 2, 3, and 4 engined aircraft all meet APPROXIMATELY the same performance criteria with 1 engine inoperative (the 3 and 4 engined aircraft do it slightly better, but only slightly. If obstacle limited, they're identical). In short, the 2 engined aricraft achieves minimum performance on 50% of available thrust, the 3 engined on 67% of available thrust, and the 4 engined on 75% of that available. That ends the discussion on the .01% of flights that an engine fails.
If we look at the 99.99% of the time that an engine DOES NOT fail, and restore the thrust lost in the 'minimum performance' discussion, the 2 engine aircraft operates at a 100% surplus of that required, the 3 holer with a 50% surplus, whilst the 4 engined cow waddles about with a mere 33% margin of excess thrust above minimum.
Given that wind shear, terrain avoidance and other 'balls to the wall thrust' situations claim infinetly more lives and hulls than dead-stick ditchings, I'll stick to the aircraft with the greatest thrust reserve to save my neck in these situations, i.e. the modern 2 engined jet transport. (I have to use the word 'infinetly' here because dividing by zero yields infinity).
Yep, I still have some residual propaganda from a 'past life' on 3 and 4 holers whilst I idly count icebergs from my B777 perch.
Join Date: Sep 2001
Location: Eagan, MN
Posts: 339
Likes: 0
Received 0 Likes
on
0 Posts
2, 3 or 4 holes, for us the choice is meaningless. We fly 'em, the money-guys buy 'em. The choices aren't ours, just the techniques for safety and comfort (and that's really illusory...we just carry out orders). Now, what'd REALLY be interesting, is a debate on long-haul engine numbers amongst people who matter....Branson, other CEO's of majors, bankers, etc. Then we'd see on what basis these decisions are really made; suppose someone proposed a single-engined ocean-crosser. D'ya think they'd find people to fly 'em? D'ya think Boston priests have uses for little boys?
