757 = Heavy? / Wake

[nike]

What is it about the 757's design that cause's it to have a particularly bad wake turbulance? So much so that normally heavy separation distance is applied to following A/C.

cheers.

[zerozero]

But I can (hopefully) steer you in the right direction.

The 757 has a super-critical wing. It doesn't work very well at slow airspeeds, thus requires a greater AoA than similiar airplanes. Hence, really mean wake turbulence.

Try a search on super critical wings and I'm sure you'll have your answers and more!

Peace.

[expedite_climb]

Hmm, not sure I would say doesnt work well at low airspeeds.
I would say it works very well at low airspeeds, all in all is a fantastic wing, from a pilots point of view.

It is however poor from a point of view of the guys behind.
Perhaps someone with an excellent pof knowledge could explain.

As regards wakes, it really is a beast. To give you an example not so long ago we t/o 1 min behind a company 757 who was 5 tonnes lighter than us. Calm winds. At 1800ft we flew through their wake, and it was violent enough to disengage the autopilot.

If it did that to a 100 tonne aeroplane - what would it do to a light a/c ? I cringe when 737's or less say theyll accept a minute behind us !

[Golden Rivet]

So much so that when NASA wanted to investigate wake turbulence what aircraft did they turn to - dear old Mr Boeings 757 !

[DanAir1-11]

Have unfortunately (for myself and pax) had the experience departing Manchester in a 748. Approx 2 - 3 mins behind the EGLL Shuttle, nearly threw us over. In all my years I have never previously, nor since (thankfully) encountered anything like it.
Very fortunate that all pax were still seated and strapped.

[nike]

ZZ- cheers I shall do.

Our reduced strength Air Force (I am trying to be polite) has just aquired a couple 757's (in fact now the only military jets in NZ bar a couple of skyhawk and aermacchi demo models for interested parties to joy ride in) hence the interest.

[zerozero]

Ok, Expedite Climb, maybe I should've used words to the effect of: "isn't quite as efficient as slow airspeeds."

That might be a little more to the point, eh?

The 757 is notorious. Nike, if you're interested, there's a link below to an accident report involving a Westwind and 757 wake.

If I'm not mistaken this was the crash that really opened people's eyes to the special hazards of 757 wake (at least in America).

The sequence of events leading up to the wake turbulence encounter demonstrates the high performance decents the 757 is capable of.

Specifically, the 757 slows to less than 150kts on a 5.6 glidepath. Meanwhile the Westwind pilot continues just "one dot high" on the Glideslope.

In this case it just wasn't good enough.

Fly safe!

IAI Westwind vs. Boeing 757 wake (http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001211X13867&key=1)

[phnuff]

Some years ago I checked into a hotel next to Orange County Airport. While I checked in, a 757 landed and on the parallel runway, a guy doing his PPL was trying to land and was flipped over; sadly he died. As I watched all the fire/ambulance vehicles swarming around, I was suddenly struck by just how real turbulence can be and it made me very very cautious which I am still to this day.

[SAM 2M]

Another possible reason for the high levels of wake are to do with the fact that the B757 inboard and outboard flaps are vitually one complete surface with no inboard aileron.

This gives a flap surface all the way from the fuselage to the aileron. This a good distace for a vortex to be generated. On a say a B767 a fair amount of this votex spills out from the inboard flap where is abutts on to the inboard high speed aileron.

SAM 2M:ok:

[wellthis]

My understanding is that the B757 wing is a very clean swept and 'fast' wing. That along with the long narrow body does not produce sufficient lift at low speeds, hence even greater need for 'high lift devices' than other jet transports, which also create higher induced drag and vortices, so much so that it is officially classified as 'heavy' in wake turbulance category.

[Pegasus77]

The next question rose during a discussion between my captain and me during my last tour:

I seem to remember, just as many colleages of mine, that the B757, which due to it's weight is categorized as Medium, should be considered, by aircraft taking off behind him, as Heavy, due to it's vortices. Therefore, flying an A320, we should wait two minutes. In Heathrow we only got 1 minute and there we started to discuss the matter (offcourse, becouse we were not sure we took 2 mins). We both seemed to remember this 757-exception, but we couldn't find it anywhere. Not in the JAR, not in our company-regulations etc.

Does anyone know where this "rule" comes from and where it is written??

Thanks!

P77

[kepor]

Don't think it is a rule...

The 757 is not classified as a heavy with reference to wake turbulence on take off. You do, however, get a bit more spacing on the approach - 4 miles vs 2.5.

Anybody got any company restrictions on take off behind a 757?

[Dan Winterland]

From AIC 17/1999 (pink 188)

'Where the leading aircraft is a B757. B707, DC8, IL62 or VC10, the minimum distance should be increased to 4nm'.

[6000PIC]

My advice , wait the 2 minutes. Have you ever hit 757 wake ? Obviously not , otherwise we wouldn`t be having this discussion. The rules are there for a reason , not for academia , but for the real world.

[Jerricho]

I remember hearing somewhere Air France have some sort of company restriction for 2 mins behind a 757.

[keithl]

The rules are there for a reason , not for academia , but for the real world

Well, that's what P77 was asking, wasn't it? Where is the Rule written? He probably knows that rules are there for a reason.

[FLEXJET]

I don't think ICAO standards talk about 757 exception, but these come from each country's CAAs.

UK CAA has different separation rules than FAA ones.

Most countries use ICAO standards, but I guess Italy and UK don't.

[Bre901]

... on same subject (http://www.pprune.org/forums/showthread.php?s=&threadid=102186)

Mods : time to merge threads ?

[FlapsOne]

I always thought it was because of the peculiarities of approach flap generated wake in the 757 that means, according to the CAA, that it is treated as a heavy when following on approach, but not for departure.

Now what you do as a matter of airmanship is entirely up to you.

One point though, if you are about to follow a 757 onto the rwy and require 2 mins (for whatever reason).............. tell ATC nice and early.

[Captain Stable]

Thanks Bre901 - done.

[Pegasus77]

This is the weird thing about it, even here everybody seems to know that there is something about the 757 regarding wakes, still I cannot find any rule in any country, or anyway not in Germany or in Holland...

Dan W... Do you have a webreference to your AIC-page?

Thanks if anyone can help me out here!

P77

[willbav8r]

Here in the US, the AIM specifies a Heavy type for wake turbulence avoidance, and includes the 757.

Perhaps that has been used by Euro operators (hence everyone seems to know, which is nice.....)?????

[Willit Run]

In the U.S. the regs were rewritten to include the 757 as a heavy. The old limit was 300,000 lbs, and its now down to 225,000(i think). And the whole reason for this was for wake seperation!
At a previous company, we had a strange DC-8 that had a gross weight of 293,000 pounds. Some guys (nuts) insisted on telling the controllers that they were not a "heavy". So, they take off at 293,000 lbs, with 1 minute seperation,and the proper DC-8 behind them took off at 250,000 and with three minute seperation. see the picture here. Some of these guys couldn't see the forest through the trees, as they were so focussed on the details and not safety or reason behind the rule. Wake turbulence is extremely violent and should not be screwed with.

[Ignition Override]

Start with the B-727 vortices. When I jogged under final approach at MSP several years ago, the descending wingtip vorteces from a 727 sounded like a pair of the weirdest whistling dust devils I could imagine, especially when they hit the trees.

A Lufthansa pilot told me years ago in SFO (as we waited for our limo vans) that his A-340 was quickly rolled to about 20-25 degrees when he departed Munich behind a 757.:uhoh: