Offloading makes the news!

[markis10]

Must be a slow news day, had to laugh at this attempt at news:

Men forced off overweight Virgin flight | NEWS.com.au

Loved this quote:

"leaving a 737 jet for the flight rather than the bigger-capacity one orginally scheduled" :mrgreen:

Staff Writers must mean contributions from work experience kids!

 

[Mal]

I suspect that it was a case of a 737-700 wanting to be used rather than a 737-800.

Technically, the 73H is a bigger airplane by about 6 meters. The 73G has a smaller payload capacity and a longer flight distance than the 73H though.

I'm suprised that 3 men (~300Kg-~350Kgs maybe including luggage) would've actually made that much difference.

 

[straitman]

I'm suprised that 3 men (~300Kg-~350Kgs maybe including luggage) would've actually made that much difference.

The line in the sand needs to be drawn somewhere . If they were really close to limits then three could take them from just outside the limit to just inside the limit.

 

[Standby]

I may be able to shed some light here having recently sat next a 737 FO from
ADL to SYD. 737's used by DJ and QF basically come in 2 specs. A high spec=greater distance and on some acft that means a chip in the engine that allow greater take off thrust or range.QF has a mix of high and low specs (the high spec cost more ) but also have a number of slightly cheaper low spec acfrt. DJ 738s are low spec which isnt really an issue except on the longhauls when the WX is V hot. The FO advsd QF quiet often is approached to carry bags for DJ ex DRW...they can take the pax but not all the bags.
Re weights.....weights and balance of the aircraft can be critical .taking those extra 2 punters can mean the diff between a nonstop flt or enroute refuel which costs ,000s in extra costs...hope the boys were given next flight with free Live TV and send to the lounge as well.
My mining mate in WA where hot conditions are freq has told me the QF717s normally have a few seats blocked off and that increases as the WX gets hotter...and they have had their engines rechipped for more power.
The Aussie climate isnt a airline friendly place at times

 

[Standby]

sorry shud have added agree total waste on newspaper inches
Now Ben Cousins arrested along with Daniel Chick...thats news

 

[Evan]

The Nadi Hump as i think it was called where QF 707's (not sure of the aircraft) had been allowed higher thrust and higher engine temps for a period of time due to the hot conditions and the high load.
E

 

[Standby]

The Nadi Hump as i think it was called where QF 707's (not sure of the aircraft) had been allowed higher thrust and higher engine temps for a period of time due to the hot conditions and the high load.
E

Thats right also the Qantas short versions of the 707 originally had injectors to boost take off performance but once engines advanced to Bypass type I think so later versions didnt need them. Thats why QF took the stubby 707 and later the 747SP..which were a real fav of mine ..always amused us that the Pan Am SP had to stop in Nadi more often than op direct vs the QF SP which I think had RR engines with a lot more poke

 

[NM]

I may be able to shed some light here having recently sat next a 737 FO from
ADL to SYD. 737's used by DJ and QF basically come in 2 specs. A high spec=greater distance and on some acft that means a chip in the engine that allow greater take off thrust or range.QF has a mix of high and low specs (the high spec cost more ) but also have a number of slightly cheaper low spec acfrt. DJ 738s are low spec which isnt really an issue except on the longhauls when the WX is V hot. The FO advsd QF quiet often is approached to carry bags for DJ ex DRW...they can take the pax but not all the bags.

Your comments started me thinking, and a little research found some interesting trivia. Both QF and DJ have in their 738/73H aircraft fleets a mix of CFM56-7B24 and CFM56-7B26 engines. The 24 and 26 designations are basically defining the thrust rating, with the 24 model rated at 23,700 lb @ 86 deg F, while the 26 model is rated at 26,100 lb @ 86 deg F, so an increase of just over 10%. The engines are basically the same and a B724 can be modified to a 7B26 spec and vice versa. There are slightly different maintenance requirements for the two, due to the 7B26 engine being able to work harder than the 7B24 engine.

Now an interesting point is that it is generally common for an aircraft type to have a higher thrust rating to allow for a higher Max Take-Off Weight (MTOW), and hence carry more fuel for more range. But QF and DJ each have all their 738/73H aircraft registered at the same MTOW, with DJ's being 79,015 kg and QF's being 78,390kg.

So given that for either operator, their registered MTOW is the same for their aircraft with each engine type, I would expect the max range would be the same, since the fuel capacity is the same and fuel burn is proportional to weight, not max engine thrust. The two engine types would be producing the same thrust at cruise anyway.

The advantage of the higher max thrust rating means the aircraft can operate from shorter runways or under hotter conditions than an aircraft with lower max thrust rating.

 

[Standby]

all correct as i mentioned a mate booked DJ once ex DRW on the midnight horror and on arr in SYD had to go round to QF to pick up his bags that DJ cudnt carry...now he tvls QF ex DRW as 767s most nights

 

[crazydave98]

Now an interesting point is that it is generally common for an aircraft type to have a higher thrust rating to allow for a higher Max Take-Off Weight (MTOW), and hence carry more fuel for more range. But QF and DJ each have all their 738/73H aircraft registered at the same MTOW, with DJ's being 79,015 kg and QF's being 78,390kg.

So given that for either operator, their registered MTOW is the same for their aircraft with each engine type, I would expect the max range would be the same, since the fuel capacity is the same and fuel burn is proportional to weight, not max engine thrust.

Almost right. MTOW is the sum of aircraft basic operating weight (empty apart from a few odds and sodds) plus fuel plus payload. We have 180 seats in our B737-800s while Qantas have 164ish (can't recall exact number). So the situation can arise where we have a higher payload and less "room" (actually weight) for fuel, and have a higher fuel burn because of the heavier payload. Therefore less range for the same aircraft.

Also, there are multiple different MTOW's available for the B737-800 (although the changes are just paper and chips as noted earlier by Standby). We have some of our 800s as High Gross Weight and some at Low Gross Weight (the leased ones that we needed to get in a hurry after Ansett fell over). The HGW are the -26 engines and the LGW have the -24 engines as NM noted, but I would be interested to know NM's source for saying that we have them registered at the same MTOWs. Obviously if a HGW aircraft is operating at close to its MTOW and has to be downgraded to a LGW, something has to give and hopefully that something won't be a few tonnes of fuel.

cheers

CrazyDave98

 

[NM]

Almost right. MTOW is the sum of aircraft basic operating weight (empty apart from a few odds and sodds) plus fuel plus payload. We have 180 seats in our B737-800s while Qantas have 164ish (can't recall exact number). So the situation can arise where we have a higher payload and less "room" (actually weight) for fuel, and have a higher fuel burn because of the heavier payload. Therefore less range for the same aircraft.

Sorry, I think my wording may not have been as clear as my thought process . I was not suggesting that QF and DJ 738/73H have the same range, but that all DJ 737-800s would have the same range as each other if carrying the same same payload, and all QF 737-800s would have the same range as each other if carrying the same payload. As you have pointed out, the different configurations between QF and DJ would lead to some variations between carries. My comparison was meant to be within each operator, not between operators.

Also, there are multiple different MTOW's available for the B737-800 (although the changes are just paper and chips as noted earlier by Standby). We have some of our 800s as High Gross Weight and some at Low Gross Weight (the leased ones that we needed to get in a hurry after Ansett fell over). The HGW are the -26 engines and the LGW have the -24 engines as NM noted, but I would be interested to know NM's source for saying that we have them registered at the same MTOWs. Obviously if a HGW aircraft is operating at close to its MTOW and has to be downgraded to a LGW, something has to give and hopefully that something won't be a few tonnes of fuel.

My source is the downloadable database from CASA or the Australian Civil Aircraft Register. I downloaded it yesterday so assume it is pretty much up to date and reflective of the actual registration details. It can be found here:

Civil aircraft register - Data files

Note that QF's fleet of HGW and LGW 73H aircraft are also all registered with the same MTOW (according to the CASA register).

Note that registered MTOW does not need to match the manufacturer's declared MTOW for the aircraft. Obviously it should not be higher, but can be lower. The aircraft cannot legally be operated above the registered MTOW. In most cases, aircraft operating fees are based on the registered MTOW of the aircraft, not the operating take-off weight, so there is a cost incentive to only register the aircraft to the lowest MTOW that is required for planned operations or you may be paying higher fees and rarely require the extra weight. The registered MTOW is noted on the aircraft registration plaque which is usually located inside the coughpit.

At least one Australian aircraft operator had a system in place where through an engineering change they could alter the registered MTOW when needed. This was doe with approval from CASA and required an engineer to replace the registration plaque inside the coughpit whenever the change was performed. This allowed the aircraft to be used for long-haul international ops where the increased weight was required, and then be "converted" for short-haul domestic ops. I am not sure how such an aircraft would show on the above mentioned Civil Aircraft Register??? I will see if I can dig out any further info on that one.

 

[crazydave98]

NM, as you point out, the actual limit is the plaque. I suspect what is on the CASA website is a generic MTOW for the type rather than the specific aircraft. We certainly don't operate our -24 engined LGW aircraft to same MTOW as the -26 engined HGW. So we can end up with an offload situation if we have to downgrade from a HGW to LGW which we of course try to avoid. But even HGW can be caught short by particular bad weather forecasts requiring diversion fuel beyond normal holding requirements or very high headwinds. I was offloaded from one of our NAN-MEL flights when we operated that route.

And as noted before, on challenging routes the HGW will have longer range with same payload because it can take extra fuel where MTOW is the limit rather than fuel volume.

All of our owned aircraft and all future deliveries will be HGW - only leased aircraft are LGW (most easy to spot by lack of winglets and live2air).

cheers

CrazyDave98

 

[NM]

NM, as you point out, the actual limit is the plaque. I suspect what is on the CASA website is a generic MTOW for the type rather than the specific aircraft. We certainly don't operate our -24 engined LGW aircraft to same MTOW as the -26 engined HGW.

Thanks for the info, Dave. Can you enlighten us to the MTOW that is actually registered for each type?

The 10% extra thrust of the B726 over the B724 is quite significant, so I would be expecting a similar ballpark for MTOW variation.

 

[crazydave98]

Generally the Low Gross Weights (such as VH-VOA, B, C & D) have MTOW 71894kg (and none of these have winglets) while the High Gross Weight have MTOW of 79015kg

 

[NM]

Generally the Low Gross Weights (such as VH-VOA, B, C & D) have MTOW 71894kg (and none of these have winglets) while the High Gross Weight have MTOW of 79015kg

Thanks Dave. That confirms my assumption of about 10% difference. Its the 79,015kg that is noted for all DJ 737-800s in the registration database.

And of course the winglets on the 73H models should also provide a range advantage when all else is equal.