737 max loses window

[smallpaul]

The design seems to be just 4 bolts to stop the door plug moving upwards (and then outwards past the stop pads). I can't see that there is any way to indicate to the flight deck the door plug is securely fitted?

That doesn't seem very much for a mechanical item that is not checked regularly.

[ATG]

airbusA346 said:

As someone put on another forum "what units do they (Boeing) use to measure their tolerances, refrigerators per football field?"

The "Tesla".

[Teddy Lop]

smallpaul said:

The design seems to be just 4 bolts to stop the door plug moving upwards (and then outwards past the stop pads). I can't see that there is any way to indicate to the flight deck the door plug is securely fitted?

That doesn't seem very much for a mechanical item that is not checked regularly.

It's a panel that should be securely fastened in place with no need to be monitored

[aeropilot]

captain_cynic said:

aeropilot said:

Eric Mc said:

Speed 3 said:

...and a lot of that was driven by Southwest who'd always had too much influence over the 737 from keeping it low to the ground at the start t

Southwest didn't exist when the original 737 was being designed. The "lowness" to the ground is nothing to do with Southwest. It was an "advantage" conferred to the original design by Boeing when they decided on the Pratt and Whitney JT8D way back in 1964 when the 737 design process began. Southwest didn't come into being until 1971/72 (if I recall correctly).

The launch customer for the original 737 was Lufthansa.

Back then, the ability to have the engines close to the ground was seen as an advantage as it allowed ease of access for maintenance. They didn't know back in the mid 1960s that they would want to be building 737s with much tubbier engines 20 years later.

I think the point being made about Southwest, wasn't in relation to the original design, but Southwest's pressure on Boeing, as one of their biggest customers for the 737, to keep trying to update such an old design, because of Southwest's criteria of keeping it low to the ground, when in reality Boeing should have pensioned off the design after the -500 series and started with a clean sheet, rather than the NG series and what has come after the NG.

It's not just southwest, a lot of budget airlines chose the 737 so they're all pressuring Boeing to avoid major changes to the design (at the same time pressuring them for a more efficient, cheaper plane).

The business model of LCCe and ULCCs is rapid turn around time, so a lot of them eschew just bridges for stairs as it speeds up turnaround time.

They're also single type fleets. The need for a separate type certification means that pilots and equipment aren't as interchangable.

But, this has been one of the criticisms of the Boeing management, whereby they have divorced themselves so much from the engineering teams with the move to Chicago etc and constantly telling the engineering teams to continually make a silk purse out of a sours ear, because the customers want to be able to have their cake and eat it, and Boeing management haven't at some point told the customers that the design has reached the end of the road, and there's no more we can safely get out of it to make it all the things you say you want from it.

[Southerner]

Eric Mc said:

There are no hard and fast rules. The 737 has been pushing the boundary because it has been around for such a long time. The planning for the 737 started around 1964 and the first aircraft flew in 1967 (the 737-100).

So, it's had a production lifespan of 60 years. I think the only large aircraft with a longer production life is the Lockheed C-130 Hercules.

737-130 of Lufthansa - the launch customer -



737 Max 9 of Alaska Airlines -



They are both recognisably 737s.

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

[MarkwG]

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

As I understand it, limitations on the undercarriage strength vs length, but I suspect there's more to it than that.

[ecs]

MarkwG said:

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

As I understand it, limitations on the undercarriage strength vs length, but I suspect there's more to it than that.

It would be a huge change which would have knock-on effects to the rest of the airframe, at which point you may as well start from scratch. The type is pushing 60 years old and was built for a world that doesn't exist anymore - just look at the differences in engine technology in the photo above!

[MarkwG]

ecs said:

MarkwG said:

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

As I understand it, limitations on the undercarriage strength vs length, but I suspect there's more to it than that.

It would be a huge change which would have knock-on effects to the rest of the airframe, at which point you may as well start from scratch. The type is pushing 60 years old and was built for a world that doesn't exist anymore - just look at the differences in engine technology in the photo above!

Indeed: it's a very long time since I did any relevant engineering, but if it were a simple problem, there'd be a simple solution, I guess.

[Eric Mc]

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

They can't use undercarriage legs any taller than currently. The wheels retract inwards and kind of meet under the centre of the fuselage. If the undercarriage legs were taller, the wheels and tyres would overlap.

The only way to fit a taller undercarriage would be to position it further out on the wing, which would mean a major wing re-design - effectively creating a new aeroplane.

Here's a picture showing how close the two sets of wheels are when retracted. The 737 is a bit unusual in that the main wheels are not covered by doors when retracted.

[airbusA346]

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

To fit longer main gear, I believe they would have to redesign the wing structures to move the attachment points outboard so that the wheels still go into the existing wheel wells (which is actually one large open space if you look inside and full of hydraulic equipment).



The engines on the 737 have been an issue since they moved away from the JT8D that were used on the 737-100/200. With the CFM56 engines that were fitted after the JT8D they had to move the engine accessories to the sides (instead of the bottom) of the engine, which meant they could gain ground clearance and it gave the distinctive non-circular air intake. The CFM LEAP-1B used on the MAX then went too far because the engines had to go up and forward.

[hidetheelephants]

Telescoping or folding undercarriage can be engineered, but it's going to weigh more, be much more expensive and the cantilever forces on the mounting points will be commensurately greater, again adding weight. Doubtless Boeing or whoever makes undercarriage for Boeing(Dowty? They make them for a lot of plane builders) will have looked at the problem and every means of getting around it and come up dry.

[aeropilot]

ecs said:

MarkwG said:

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

As I understand it, limitations on the undercarriage strength vs length, but I suspect there's more to it than that.

It would be a huge change which would have knock-on effects to the rest of the airframe, at which point you may as well start from scratch. The type is pushing 60 years old and was built for a world that doesn't exist anymore - just look at the differences in engine technology in the photo above!

Exactly. It would effectively be a clean sheet design and not the ancient old 737 that the want their cake and eat it customers want.

The thing is Boeing even had a higher up, newer aircraft in the 757, which has come and gone within the 737 timeframe.

The other issue is they are still making new NG's for all the military P-8 and E-7 orders

[2xChevrons]

MarkwG said:

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

As I understand it, limitations on the undercarriage strength vs length, but I suspect there's more to it than that.

As I understand it MCAS wasn't installed on the MAX because the new engines/their position made it literally unstable - MCAS isn't covering up inherently poor or dangerous flight characteristics.

It's that, due to the more powerful and repositioned engines the MAX's flight characteristics differed too much from the 737 Classic and NG generations in certain conditions and phases of flight, especially stall recovery. How the MAX flew wasn't dangerous, but was too different from previous 737s to fall under the same type rating for crew training purposes - without MCAS crews would need much longer, more detailed and costlier conversion courses. With MCAS artificially making the MAX fly more like an NG by automatically controlling the tailplane trim to compensate for the big, forward-slung engines' pitch effects, that could be avoided.

The MAX exists as Boeing's counter to the A320neo, which like the MAX is an established and high-selling model updated with much more efficient engines, aerodynamic improvements and avionics updates. Airbus had already assured the market that the neo would share the same type rating as the existing A320. Of course, Airbus have the advantage of the A320 being a much newer airframe, designed for high-bypass engines and not cramped by considerations for being loaded by manual labour at airfields previously served by DC-3s and Convair 240s like the 737 was.

Boeing was weighing up whether to do another 'stretch' of the 737 design (designed in the 1960s and based on a fuselage from the 1950s) or commit to an all-new '797' replacement (I believe there was also an idea in the 2000s to produce a 737 replacement using 757 parts when that ended production) - but that would cause a massive hurdle for operators like Southwest and Ryanair which have finely-honed their operations down to the last fraction of a cent/penny using standardised fleets of 737s. With Airbus already promising continuity between the A320 and the A320neo, Boeing felt it couldn't take that risk and so committed to the MAX - fitting new engines to the airframe and using MCAS to keep the flight characteristics where they needed to be.

[Southerner]

2xChevrons said:

MarkwG said:

Southerner said:

Interesting. So, for example what would there be to prevent Boeing from making the whole aircraft higher and being able to fit the larger engines ‘properly’ on the Max variant, rather than bodging it by making the thing unstable and then having to fit software to essentially correct it?

As I understand it, limitations on the undercarriage strength vs length, but I suspect there's more to it than that.

As I understand it MCAS wasn't installed on the MAX because the new engines/their position made it literally unstable - MCAS isn't covering up inherently poor or dangerous flight characteristics.

It's that, due to the more powerful and repositioned engines the MAX's flight characteristics differed too much from the 737 Classic and NG generations in certain conditions and phases of flight, especially stall recovery. How the MAX flew wasn't dangerous, but was too different from previous 737s to fall under the same type rating for crew training purposes - without MCAS crews would need much longer, more detailed and costlier conversion courses. With MCAS artificially making the MAX fly more like an NG by automatically controlling the tailplane trim to compensate for the big, forward-slung engines' pitch effects, that could be avoided.

The MAX exists as Boeing's counter to the A320neo, which like the MAX is an established and high-selling model updated with much more efficient engines, aerodynamic improvements and avionics updates. Airbus had already assured the market that the neo would share the same type rating as the existing A320. Of course, Airbus have the advantage of the A320 being a much newer airframe, designed for high-bypass engines and not cramped by considerations for being loaded by manual labour at airfields previously served by DC-3s and Convair 240s like the 737 was.

Boeing was weighing up whether to do another 'stretch' of the 737 design (designed in the 1960s and based on a fuselage from the 1950s) or commit to an all-new '797' replacement (I believe there was also an idea in the 2000s to produce a 737 replacement using 757 parts when that ended production) - but that would cause a massive hurdle for operators like Southwest and Ryanair which have finely-honed their operations down to the last fraction of a cent/penny using standardised fleets of 737s. With Airbus already promising continuity between the A320 and the A320neo, Boeing felt it couldn't take that risk and so committed to the MAX - fitting new engines to the airframe and using MCAS to keep the flight characteristics where they needed to be.

That’s a very interesting post; thanks!

[Speed 3]

GliderRider said:

b0rk said:

I’m curious if you have any insight into why Airbus decided to offer the NEO, it appears externally that the A320 family was in the naughties as much of a cash cow for Airbus as the NG was for Boeing. Airbus committing a $1bn+ to offer an improved product without any realistic chance of altering market dynamics vs Boeing seems an interesting and aggressive decision. Both manufacturers had I recall very long order backlogs at that point.

Where Airbus concerned about other manufacturers Bombardier? Embraer? capturing the A319 market and possibly some of the A320 market by stretching an existing or proposed design into that space? A stretch of a smaller product would I assume hold structural advantages over a shrink of a larger product.

I suppose Boeing not wanting to be first with a clean sheet design was possibly based on the assumption that Airbus would counter with an improved A320 at a lower unit sale price.

Wikipedia in its article on the A320NEO, cites the Republic Airways Holdings/Frontier Airlines order for 40 Bombardier CS300s as pushing Airbus into going ahead with the re-engining. John Leahy, Airbus's 'COO-customers' could see that if the CS300 got a market foothold, Bombardier would enlarge the aircraft, thus creating a direct competitor to the A320 series.
Eventually Airbus bought the CS300 programme from Bombardier and rebranded it as the A220.

Edited by GliderRider on Wednesday 10th January 00:59

That was a catalyst. At the time fuel price was heading north quickly and the NEO promised up to 16-18% better economy (at least half from the new engine and the balance from aerodynamic improvements). Initially Airbus pitched it as "it'll cost x more to buy because you're getting a bit more than financing x in fuel saving". That didn't work with the airlines who wanted the bulk of the saving, more of a cost plus margin. When Airbus changed their pricing model it started to fly !

[budgie smuggler]

2xChevrons said:

As I understand it MCAS wasn't installed on the MAX because the new engines/their position made it literally unstable - MCAS isn't covering up inherently poor or dangerous flight characteristics.

It's that, due to the more powerful and repositioned engines the MAX's flight characteristics differed too much from the 737 Classic and NG generations in certain conditions and phases of flight, especially stall recovery. How the MAX flew wasn't dangerous, but was too different from previous 737s to fall under the same type rating for crew training purposes - without MCAS crews would need much longer, more detailed and costlier conversion courses. With MCAS artificially making the MAX fly more like an NG by automatically controlling the tailplane trim to compensate for the big, forward-slung engines' pitch effects, that could be avoided.

The MAX exists as Boeing's counter to the A320neo, which like the MAX is an established and high-selling model updated with much more efficient engines, aerodynamic improvements and avionics updates. Airbus had already assured the market that the neo would share the same type rating as the existing A320. Of course, Airbus have the advantage of the A320 being a much newer airframe, designed for high-bypass engines and not cramped by considerations for being loaded by manual labour at airfields previously served by DC-3s and Convair 240s like the 737 was.

Boeing was weighing up whether to do another 'stretch' of the 737 design (designed in the 1960s and based on a fuselage from the 1950s) or commit to an all-new '797' replacement (I believe there was also an idea in the 2000s to produce a 737 replacement using 757 parts when that ended production) - but that would cause a massive hurdle for operators like Southwest and Ryanair which have finely-honed their operations down to the last fraction of a cent/penny using standardised fleets of 737s. With Airbus already promising continuity between the A320 and the A320neo, Boeing felt it couldn't take that risk and so committed to the MAX - fitting new engines to the airframe and using MCAS to keep the flight characteristics where they needed to be.

Without MCAS the MAX could not meet airworthiness regs, as the pitch-up effect that their engine position caused in some circumstances is not allowed.

[outnumbered]

budgie smuggler said:

Without MCAS the MAX could not meet airworthiness regs, as the pitch-up effect that their engine position caused in some circumstances is not allowed.

Do you have a reference for that ? My understanding was the same as 2xChevrons, that MCAS was only required because it provided a way to avoid an additional type approval.

[budgie smuggler]

outnumbered said:

budgie smuggler said:

Without MCAS the MAX could not meet airworthiness regs, as the pitch-up effect that their engine position caused in some circumstances is not allowed.

Do you have a reference for that ? My understanding was the same as 2xChevrons, that MCAS was only required because it provided a way to avoid an additional type approval.

Sure

cfr said:

§ 25.203 Stall characteristics.

(a) It must be possible to produce and to correct roll and yaw by unreversed use of the aileron and rudder controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.

eta, mentioned in the 'background' section here
http://www.b737.org.uk/mcas.htm#background

[Speed 3]

Service Bulletin is out

[aeropilot]

Speed 3 said:

Service Bulletin is out