Return versus Diversion

[Chock 17,769]

What has to be borne in mind with the 747, is that it was a product of an era when four engines was a sensible precaution for long distance over water operations. In fact the 747 was designed to be able to ferry a fifth engine on the wing because of the expected lesser reliability of the  P&W JT9D, which let's not forget, was designed for use on the C-5 Galaxy, which of course also featured four engines for the same reliability reasoning. But as engines became more reliable and fuel costs became a concern in the late '60s and early '70s, that led to a bunch of Tri-Jets, most notably the DC-10, L-1011, 727 and Trident, and people were willing to trust flying on three engines because of that increased reliability. Then of course as reliability of engines increased further, along came ETOPs and a bunch of big twins, A300, A330, 767, 777. Now nobody blinks an eye at one of these big twins setting off across the Atlantic, in fact, the only majorly important quad jet that's been designed since the 747 (disregarding the Avro RJ) is the A340, and that's only because Quantas needed it for journeys over the Pacific where ETOPs wasn't economical to apply.

 

So yes the 747 was designed in the Sixties with four engines, but they aren't still hanging the original less reliable JT9Ds under the wings of 747s these days, that BA 747 will have had RB211s under its wings, which we can note, was an engine originally designed for the L-1011 TriJet. :-)

[BlueStar 323]

flying round in circles over LA for 40-60 minutes dumping/burning off fuel followed by a landing at close to MLW?

 

 

The B744 is certified for landing at MGTOW at a sink rate of 6 feet per second and 10 feet per second at MGLW.  Most landing descent  rates are in the 2-3 feet per second range and a "hard" landing would be 6 feet per second. 

 

I am not a big fan of holding to burn off fuel or dumping fuel to get down to MGLW.  The B737, B757, some B767s, and the B777 are not required to have a fuel jettisoning system per FARs. 

 

If I couldn't land with a descent rate of 6 feet per second at MGTOW then I should be on the ramp loading freight instead of flying it. :smile:

 

blaustern

[Flamin_Squirrel 71]

the only majorly important quad jet that's been designed since the 747 (disregarding the Avro RJ) is the A340

 

What about the A380?! 

 

 

 

If I couldn't land with a descent rate of 6 feet per second at MGTOW then I should be on the ramp loading freight instead of flying it.

 

Surely it's not just the touch down; you've got to stop once you're on the ground. Vref for a MGTOW is ~190kts and landing distances are enormous. 

[Copper. 78]

Yeah I was going to mention the overweight landing ability, but chose not to as it is seperate to the points I was making.

 

Of course, there are a number of factors to consider when planning a return, least of which are the weights, approach speeds, flap setting, stopping distances and braking perf leading to runway adequacy/condition, sink rate, touchdown g-forces, Boeing symmetrical reverse thrust policy, list goes on and on.

 

You guys have shown good CRM.

[Chock 17,769]

What about the A380?! 

 

True, but again, the A380 is another one which is specifically for situations where ETOPs isn't economical so it again is akin to the 340 as far as its reason for being is, but with more seats, plus it's not able to get into every airport that most other airliners can get into since it requires some quite fancy facilities and it's a BUFF, so not least of which is taxiways that can handle it lol. And of course much of its success is owing to airlines from a lot of Arabic countries go out of their way not to buy American aircraft lol.

[phil747fan 14]

Having flown long haul on twins and quads (A330-A340) I'm with Simon on this.

During my first A340 training one of the sim scenario was an engine failure right overhead BIKF enroute to KJFK... After 10 years on twins the first thing I did was looking for an adequate airport on my ND.

Only later I realised our altitude penalty was barely 2000ft, we were still significantly overweight and we could have comfortably made the east coast or get back to Europe, if commercially required.

I learnt I had to change my mindset and that was the whole training objective.

As per my operator's OM-A an engine failure on a quad does not qualify as land ASAP, unless of course other risks are present (other systems damage as a result, leaks etc).

Three engine ferry regulations are for dispatch purpose, different ballgame.

As per 2 engine failure (on A340) it is a normal failure practiced at all sim proficiency checks, the aircraft flies as well as a A330 on single engine... I'm not as expert on Boeing but I would presume it would be the same , if not better.

Regards

Mike,

 

while enroute is different story than starting a complete flight between 9 and 11 hours with only 3 engines in that case we are more on the scenario written of ferry ....airbus or boeing in that case as we had both for a while ... for the flights we were doing there is no way that at 400 feet a captain will continue the flight. i do not know about your airline policies or the regulators.

 

if you read the report of that incident they finished with a mayday at the end and 5.8t remained in the tanks ...

 

https://assets.publishing.service.gov.uk/media/542302bfe5274a1317000bd7/Boeing_747-436__G-BNLG_06-06.pdf

 

depending on the regulations the diversion can be made for safety reasons and the crew is the only one but when ops is in mind it can be a little different even if the crew is the only one in the air .... 

 

glad to have that conversation not in the air ....

 

Phil

[BlueStar 323]

 

 

Surely it's not just the touch down; you've got to stop once you're on the ground. Vref for a MGTOW is ~190kts and landing distances are enormous

 

Your landing speeds and stopping distances will be much shorter than the take off distances and speeds. 

 

blaustern

[Flamin_Squirrel 71]

Your landing speeds and stopping distances will be much shorter than the take off distances and speeds. 

 

blaustern

 

According to TOPCAT, at MGTOW, V2 is 181 and Vref is 191, so no landing speeds are not less in this case.

[BlueStar 323]

 

 

According to TOPCAT, at MGTOW, V2 is 181 and Vref is 191, so no landing speeds are not less in this case.

 

You are mixing apples and oranges.  V2 is a departure speed and  Vref is a landing speed. 

 

Vref is the speed at 35 feet above the landing threshold.    At 35 feet (B744) the throttles will be going to Flight idle on and the landing flare started.  With more flaps and no thrust the aircraft will decelerate rapidly as it approaches touchdown. 

 

blaustern

[Flamin_Squirrel 71]

You are mixing apples and oranges.  V2 is a departure speed and  Vref is a landing speed. 

 

Vref is the speed at 35 feet above the landing threshold.    At 35 feet (B744) the throttles will be going to Flight idle on and the landing flare started.  With more flaps and no thrust the aircraft will decelerate rapidly as it approaches touchdown. 

 

blaustern

 

So what figures for takeoff/landing would you like to use then? You keep telling me I'm wrong without providing your own numbers/information.

[skelsey 765]

 

The B744 is certified for landing at MGTOW at a sink rate of 6 feet per second and 10 feet per second at MGLW.  Most landing descent  rates are in the 2-3 feet per second range and a "hard" landing would be 6 feet per second. 
 
I am not a big fan of holding to burn off fuel or dumping fuel to get down to MGLW.  The B737, B757, some B767s, and the B777 are not required to have a fuel jettisoning system per FARs. 
 
If I couldn't land with a descent rate of 6 feet per second at MGTOW then I should be on the ramp loading freight instead of flying it.

 

Some rough back of the fag packet calculations from the QRH.

 

I make Vref25 (given that Vref30 of 184kt is above the Flap 30 placard of 180kt) at MTOW 192kt for the B747.

 

With a properly-executed flare touchdown should occur at Vref to Vref-5 (having flown the approach at Vref + 5 - or around 197kt, which is still rather close to the Flap 25 placard of 205 kt -- let's hope there's no gust factor to add...).

 

We'll start with landing distance.

 

With Max manual braking, landing distance at MTOW based on the speeds above I make 2710m. Doesn't sound so bad, eh? We'll get on to that.

 

With autobrake 2 the required landing distance becomes 4320m

 

OK, let's have a look at the brake energy tables.

 

The maximum brakes on speed in the QRH brake energy table is 180 kias, so we'll use that (note - this is a little lower than our actual Vref).

 

At sea level, ISA, that gives us a reference brake energy per brake of 76.5 million foot-pounds.

 

If we then go down to the adjusted brake energy -- for max manual braking on landing, that gives us a reference brake energy of around 66.5 million foot-pounds. With autobrake 2, the reference energy is still around 50 million foot-pounds, and even with autobrake 1 the reference energy is about 45 million foot-pounds per brake (if you were wondering, the LDR with autobrake 1 is around 4,810m). 

 

All of those are in the fuse plug melt zone.

 

So, yes, you can land a B747 safely at MTOW. But you'd a) better have a very long runway and b) you won't be using the aeroplane again for a while until it's had several tyres changed.

 

To me, neither of those things seem a particularly proportionate response to a simple compressor stall. If you're on fire, sure, but otherwise it's a great way to trash a perfectly airworthy aeroplane.

[phil747fan 14]

never heard about operations letting a plane continuing the flight after an engine out at the beginning of the flight BAW is the only carrier that did that.

 

staying on hold and dumping fuel is what is to be done or was done with the 3 operators i work for.

 

the discussions that came after the report of BAW  has been always with the same ending, your burn your fuel. you dump the fuel but you do not continue your flight. the 747-400 is meant to operate with 4 engines on regular operations, we are talking about a flight that last at least 9 to 11 hours or more on three engines. but in the same time we operated with 180 min as EROPS ....

 

not discussing the fact that the 747400 cannot do it but why not cutting one engine to save the wear and tear? ....

[BlueStar 323]

 

 

So, yes, you can land a B747 safely at MTOW. But you'd a) better have a very long runway and you won't be using the aeroplane again for a while until it's had several tyres changed.

 

Simon,

 

The B747-400B is certified to land in just a touch over 7,000 feet at MGTOW with Flaps25 and maximum manual brakes and no reverse thrust.  Of course YMMV on a contaminated runway.  The MD-11 has very similar numbers.

 

blaustern

[phil747fan 14]

oh BTW BAW said they wont do that anymore in USA air ....

[skelsey 765]

Hi Wilhelm,

 

 

 

The B747-400B is certified to land in just a touch over 7,000 feet at MGTOW with Flaps25 and maximum manual brakes and no reverse thrust.

 

What is a 747-400B? Where are you getting your numbers from? At 395 tonnes (i.e. slightly under but near as dammit MTOW) the best I can get from the QRH with F25 is 2660m with max manual braking, which is just over 8,000ft.

 

Regardless, as I said in my post you can do it, but as you will know with your experience that it is not just about landing distance alone. The big limiting factor is the brake energy and if you land a 747-400 on an 8,000ft runway at MTOW you will unquestionably melt the brakes and fuse plugs. If you are on fire then clearly this is a better outcome than burning in the air. However, ending up disabled on the runway with 16 flat tyres and burning brakes to me, again, would seem to be a rather extreme and disproportionate response to a compressor stall. Do you not agree?

 

 

 

never heard about operations letting a plane continuing the flight after an engine out at the beginning of the flight BAW is the only carrier that did that.

 

That is not true. If you read the report, you will see that several other carriers had similar or identical flight continuation policies, and from a legal perspective Boeing, the CAA and the FAA (at the time) all agreed that a single engine failure on a four-engined aircraft with no other aggravating factors is not a case for immediate panic and diversion. The airframe manufacturer, the engine manufacturer, the regulators and the operator all agreed that the aircraft was in a perfectly airworthy condition to continue the flight, that there no risk of further damage to the engine or airframe as a result and that:

 

 

no evidence was found to suggest that the aircraft systems would be affected by the loss of an engine.

 

Again, I'll stress that the Commander didn't make an immediate decision to continue the flight to destination. The decision was to continue, assess the situation, route in such a way that ensured there were plenty of options available and divert if anything adverse appeared at any point during the flight. What is unreasonable about that, given that the decision was considered and made within the framework of the FCOM, QRH, well-established written and regulator-approved operator policy and the law?