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Major Differences Between 75 And 76?  
User currently offlineZionstrat From United States of America, joined Apr 2001, 226 posts, RR: 0
Posted (12 years 3 days 6 hours ago) and read 2351 times:

On a recent thread I learned for the first time that 757 and 767 flap settings result in different flap configurations.

http://www.airliners.net/discussions/tech_ops/read.main/44207/

Since there is a blanket rating treating them as one type, I've always assumed they were minimal, but would be interested in knowing what the major differences are (outside of the obvious, size, isles, engines etc). Are there any lists that could be easily referenced?

Thanks!




16 replies: All unread, jump to last
 
User currently offlineLMP737 From , joined Dec 1969, posts, RR:
Reply 1, posted (12 years 3 days 6 hours ago) and read 2330 times:

Aside from what you mentioned there really are not that many. In fact the 757 & 767 have around a 60% spare parts commonality if I remember correctly. Maybe someone else could shed more light on the subject. Here's one difference. When the 757 and 767 came out the 767 had vacuum lavs and the 757 had the chemical lavs. Now vacuum lavs and chemical lavs are an option on the 757.

User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 2, posted (12 years 3 days 3 hours ago) and read 2310 times:

It depends what kind of differences you mean? General Handling or Technical? There are more than you would think, from a pilots point of view in General Handling terms.

Will provide the details if you want them.



I used to love the smell of Jet-A in the morning...
User currently offlineRussianplnelvr From United States of America, joined Sep 2001, 228 posts, RR: 0
Reply 3, posted (12 years 3 days 2 hours ago) and read 2286 times:

I have a few questions and I apologize if they are stupid questions.

1. Between the 757/767, which plane is easier to fly?

2. Does each 757 or 767 handle differently another identical one?


User currently offlineCdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 27
Reply 4, posted (12 years 3 days 1 hour ago) and read 2274 times:

B757 - Engine Control mechanical
B767 - Electronically Controlled (FADEC)*

B757 - No Fuel Jettison Capability (No need for it since Max TO and LDG weights are so close)
B767 - Fuel Jettison Capability (Have also heard that is also an option)

B757 - No Inboard Aileron
B767 - Inboard Aileron that just about every widebody has

Off the head, those are the only significant differences that I can think of. And the only on that a flightcrew what even notice a difference in is the fuel jettison. The inboard aileron doesn't make the aircraft fly any different. The throttles on FADEC controlled aircraft are smoother in transit, but with the autpilot controlling thrust 98% of the time - who notices.

Regarding the Automatic Flight Control Systems and the FMC, you'd be hard pressed to find any significant differences between the 2 aircraft.

There are differences in the way the systems carry out certain functions, but flightcrews won't see it in the flightdeck.
Keep in mind, I am comparing a B757-200 to a B767-200. The B757 is very different than the B767-400. I don't care about that whole crew-common crap. That airplane is different than a B757. As a technician, I can go from a B757-200 right into a B767-200 and feel like I didn't leave. It takes a couple of minutes in a B767-400 to get acclimated.
Even the way systems handle functions btwn the B757 and the B767-400 is totally different.

*FADEC controlled B767s can be found on the newer B767s with Cf6-80 powerplants.

--------------------
Russianplnlvr

We operate the B757-200 and -300 with RB211s, B767-200 and -400 with CF6-80s.
I'm no pilot,but having talking to some, the 3 aircraft fly very different. Every B757/B767 crew that I have talked to LOVES flying the B767-200. Then the B757-200 and last the B67-400. They say they love the way the B767-200 climbs and the power it has. I don't quite understand that because that B757 climbs like a rocket with those Rb211s. But thats what I've heard.


User currently offlineLMP737 From , joined Dec 1969, posts, RR:
Reply 5, posted (12 years 3 days ago) and read 2266 times:

Cdfmxtech:

At least one of us is one the ball today. Guess that's what happens when it's your day off, you leave the brain at work.

On a little side note PW powered 757's use FADEC. And don't forget when you enter the 767 cockpit you step up, on the 757 you step down.


User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 6, posted (12 years 3 days ago) and read 2274 times:

Russianplnelvr,

We operate the 757-200, 767-200 and 767-300. The 767-200 is by far the easiest and most pleasant to operate. It's a joy to fly, very responsive, very forgiving, climbs like a raped ape.

The 757-200 comes a close second and the 767-300 a close third. The 767-300 is a nice aircraft, but it is not as forgiving and you can get yourself into trouble more easily with it.

Cdfmxtech,

Yes fuel dump is an option on the 767s. Autoflight and FMC differences are, as you say, few and far between. But for the 767-300 the FL CH mode is more subtle. The thrust levers will not open / shut fully for climbs / descents of 2,000ft or less like they do on the 757. Also GA thrust works a bit differently on the 76, during a go-around the thrust levers open to a value appropriate to achieve a climb rate of 2,000 fpm. The 757 applies maximum GA thrust then reduces power to maintain a 2,000 fpm climb.

Trust me it makes your heart skip a beat when the 757 is rocketing into the sky on a go-around and then the thrust suddenly comes back!

Generally the 757-200 and 767-200 are very similar aircraft to fly, and the 767-300 is a bit different. Key differences are (for the 763 against the 752):

Takeoff Rotation rate
Rudder Application and Pitch input with an engine failure after t/o
Approach attitude
Flare height
Landing control inputs
Flap Retraction Times
Flap Load Relief (it has it!)
Flap setting values do not correspond to the true flap angle

Can explain each one further if anyone is interested?

Rick.



I used to love the smell of Jet-A in the morning...
User currently offlineMhsieh From United States of America, joined Jul 2000, 332 posts, RR: 0
Reply 7, posted (12 years 2 days 22 hours ago) and read 2244 times:

Can someone comment on the 757 and 767 flap design..757 seems to have the traditional flap guide rail with flaps driven by jackscrew while the 767 has some kind of hinge design driven by a rotary actuator....seems the 767 flaps are more simplified....

User currently offlineCdfmxtech From United States of America, joined Jul 2000, 1338 posts, RR: 27
Reply 8, posted (12 years 2 days 22 hours ago) and read 2238 times:

Comment any furtehr would be too complicated, so I'll just Confirm??

B757 - BallScrew Actuator (jackscrew)
B767 - Rotary Actuator


User currently offlineMhsieh From United States of America, joined Jul 2000, 332 posts, RR: 0
Reply 9, posted (12 years 2 days 16 hours ago) and read 2208 times:

Are there any reduction gears in the rotary actuator ie. how is torque transmitted from the main flap drive shaft to the rotary actuator??
Which system is easier to maintain??
Thanks


User currently offlineGE From Singapore, joined Mar 2000, 320 posts, RR: 6
Reply 10, posted (12 years 2 days 13 hours ago) and read 2192 times:

Rick767:
I would really appreciate it if you could please elaborate on:
rotation rates
approach attitude
flare height
flap settings not corresponding to true flap angles

Thank you Richard!


Regards,
Russell J


User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 11, posted (12 years 2 days 7 hours ago) and read 2160 times:

Russell,

No problem. Bear in mind these are differences for the 767-300, where the differences exist against the 752/762

Rotation Rate

With the longer fuselage, this must be lower than for the 752/762. Theoretically, about 2.5 degrees per second (where the 752/762 is 3 degrees per second).

The rotation rate is very important especially in the case of an engine failure since the minimum tail clearance is only 12 inches. This minimum clearance occurs in the 763 after lift-off.

Approach Attitude

Typically the nose-up attitude is about 1 degree lower on approach on the 763 than the 752/762, leading to a typical approach attitude of 1 to 3 degrees on the 763, rather than about 2 to 4 degrees.

It sounds a small difference but in my experience for normal landing weights the approach is noticeably flatter on the 763.

Flare Height

Flare Height is slightly higher on the 767 than on the 757 - 25 feet Radio Altitude rather than 20 feet. For normal pitch attitudes the main wheels on the 767 are 4 feet lower than on the 757.

As a general rule, there is less time between the automated "30 ft" call and the start of the flare. The time between the "30ft" call and the start of the flare on the 757 is suggested at 1 second, but one second is a long time in aviation so about 0.5 seconds after the call for the 763.

Remember also that the pitch attitude on completion of the flare (waiting for the a/c to settle onto the runway) is about 4 to 5 degrees nose-up, compared to 5 to 6 degrees on the 757.

Flap Angles

For the 767-300, the readings on the flap gauge do not represent the true flap angle. They are used purely to achieve commonality with the Boeing 757.

On the 767, Flap 1 (for example) only extends the leading edge slats (no flap at all). Flap 15 is similar to Flap 20 on the Boeing 757 and Flap 30 is in reality at an angle of more than 30 degrees.

Airbus have got it right here IMO, give the flap configurations numbers (1, 2, 3, Full) since the 767-300 proves the point that the actual angle the flap is extended is not relevant.

Hope this proved of some interest.



I used to love the smell of Jet-A in the morning...
User currently offlineZionstrat From United States of America, joined Apr 2001, 226 posts, RR: 0
Reply 12, posted (12 years 1 day 19 hours ago) and read 2115 times:

Great info- Much thanks!

User currently offlineAJ From Australia, joined Nov 1999, 2386 posts, RR: 24
Reply 13, posted (12 years 1 day 19 hours ago) and read 2115 times:

Rick, it might interest you to know that some of our B767-300s print a 'Pilot Only' takeoff report, which includes speeds, pitch rate, pitch and tail clearance in feet taken at 1/4 second intervals. A 'G' or 'A' indicates the position of the air/ground switch of each readout. Fascinating! (sometimes concerning)

User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 14, posted (12 years 1 day 15 hours ago) and read 2096 times:

AJ,

That's an interesting little system you have there. I bet it would be a sobering read every so often!  Sad



I used to love the smell of Jet-A in the morning...
User currently offlineGE From Singapore, joined Mar 2000, 320 posts, RR: 6
Reply 15, posted (12 years 1 day 14 hours ago) and read 2094 times:

Rick767:
Thank you so much! I find this info very interesting. You have certainly enlightened me on many things which I never knew before. Big grin


Regards,
Russell J


User currently offlineRick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 51
Reply 16, posted (12 years 1 day 5 hours ago) and read 2066 times:

Russell,

No problem at all I enjoy sharing what knowledge I do have with others! Though I admit I cheated a bit and looked in the Training Manual... just to check of course Big grin

Cheers.



I used to love the smell of Jet-A in the morning...
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