You are of course correct. An aircraft operator would normally order an aircraft to be in the configuration they wished to use it in service. Given the length of time it takes to make an aeroplane, there may be reasons why an operator might want to change the configuration before receipt, but that would normally involve paying extra for the deviation from the original order.
They may decide to change the configuration after receipt but before going into service, or after the aircraft has been in service for a while.
Reasons for deciding to change a configuration could include falling or rising operational requirements, or falling or rising passenger numbers, a change of regime at an existing or proposed destination, a volcano, or armed conflict to name a few.
The fact still remains that by ordering (or later changing) a seat plan that allowed two exit doors to be blanked, the spaces mandated by air safety requirements around those doors can be deleted if certain requirements are met, meaning that three (or possibly four) extra seats could be fitted.
Some Alaska Airlines 737 Max 9s have two toilets on the left at the back, and one toilet on the right at the back. The extra space in front of the right hand single toilet can be used for many things.
Depending on seat spacing, this could be used for extra seats, or storage of emergency medical equipment, or curtains and a drop down bed as a rest area for cabin crew.
On some variations of Alaska Airlines 737 Max 9s, they adopt a varying seat spacing on the right, aft of the wing exits, compared to the fixed seat spacing on the lift. This allows the space in front of the right hand toilets to accommodate an extra row of seats.
A plan view of this seat configuration shows the seats on both sides of the aircraft immediately behind the over-wing exits to be in direct alignment, whereas as one progresses rearwards, the rows of seats become increasingly staggered compared to the seats on the left.
Doors and exit hatches must have more space. Seats in front of an exit row may have limited or even zero movement such that they cannot be reclined much, or at all, so they canât stick out into the exit path in an emergency.
Grabbing these few extra centimetres by deleting an exit row (plugging the door-hole), plus grabbing an extra centimetre or two for each row of seats on the right, plus adding the perhaps half a metre of spare room just in front of the tight hand toilet will give just enough room to fit in another row of seats compared with the same seat spacing if the doors are left operational.
Itâs all down to pence or cents saved/made per mile of kilometre flown. Six more economy seats without compromising the addition of 24 premier seats, compared with leaving the doors operational, whilst sill meeting air safety standards is worth it in the operators view.
Bluster away ⊠your assertion of responsibility for the installation of the configuration has been proved incorrect.
The boss of Boeing has admitted the planemaker was at fault after one of its aircraft suffered a door blow-out shortly after take-off in the US.
On Tuesday, Boeingâs president and chief executive Dave Calhoun said the firm was âacknowledging our mistakeâ.
Speaking to Boeing staff, Mr Calhoun said: âWeâre going to approach this number one acknowledging our mistake. Weâre going to approach it with 100% and complete transparency every step of the way.â
Mr Calhoun reassured staff that Boeing would work with the NTSB to investigate the cause of the accident.
Bolts havenât been found and some found loose on other planes
Just did a back of the envelop calculation on the pressure on that door.
At 16000 ft the atmospheric pressure is about 8psi, most planes are pressurised to about 11psi no matter their height (obviously not while the doors are open on the ground).
The pictures of the door plug make it look about 3ft by 5ft assuming a 3psi difference between the internal and external pressure then the door is subject to a pressure of about 3 tons (6480 lbs or 2940kg) pushing it outwards. If the door is bigger than this estimate (or flying higher) then there is more pressure on it and vice versa.
Apparently it is not like normal cabin doors which are larger than the hole they seal so are held in place by the difference in pressure (and some locking mechanism) but these plugs are just held in with 4 bolts and some stop plugs.
Interesting eh?
Youâve also got the suction (aerofoil) effect of the faster airflow around the fuselage compared to the true airspeed that will reduce the effective pressure at altitude compared to the static altitude pressure.
That would slightly increase the pressure drop from inside to outside that will increase the effective internal force trying to push the door plug out.
As you correctly surmised, a small pressure over a large area is a large force.
The locking mechanisms on standard civil aircraft doors are phenomenal and designed such that they can be opened when the fuselage and door are covered by several centimetres of ice by the slightest member of a cabin crew. They also open inwards, even the over-wing hatches.
The FAA grounded dozens of the jets following that Alaska Airlines incident, and Boeing on Monday issued instructions for inspecting the jets, which were approved by the FAA.
Revisions to multi-operator messages, which contain the instructions, can be based on feedback from airlines, the company or inspectors.
âBoeing offered an initial version of instructions yesterday which they are now revising because of feedback received in response. Upon receiving the revised version of instructions from Boeing the FAA will conduct a thorough review,â the FAA said in a statement Tuesday.
Presumably, out of an abundance of caution.
Yes, I thought this was the case on pretty much all doors - normal entry doors, emergency doors, freight doors. I recall that the BAe 146 had a problem because one of its freight doors did not have this configuration - although my memory have failed me here. Nonetheless the wider-than-the-hole arrangement is pretty standard and very safe. Why the airworthiness authorities allowed a door plug to avoid this configuration seems very unusual.
Apparently, plug doors have other uses, apart from aircraft, including space craft and deep-sea vehicles:
Airline regulators will not be rushed into clearing grounded Boeing 737 Max 9 planes after a mid-air blowout, the US government has said. The aircraft, which were suspended in the US following an incident on an Alaska Airlines flight âneed to be 100% safeâ, said Transportation Secretary Pete Buttigieg.
Boeingâs boss, Dave Calhoun, described the incident as a âquality escapeâ. It means the incident was caused by some failure in quality control in the plane, which had been in service for just eight weeks before the blowout.
Mr Calhoun told CNBC that there were still questions that need to be answered about how the incident was allowed to happen. âWhat broke down in our gauntlet of inspections? What broke down in the original work that allowed for that escape to happen,â he said.
Quite ⊠
A class-action lawsuit was filed against Spirit AeroSystems in New York federal court on December 19 that alleged it experienced âsustained quality failuresâ in its products.
The suit was filed on behalf of investors of the company, which was previously a manufacturing unit of Boeing until 2005.
The lawsuit filed against Spirit AeroSystems alleges the company had manufacturing problems and includes a complaint from one employee who claimed there was an âexcessive amount of defectsâ in an email sent to a company executive.
Although the complaints do not specifically refer to door plugs, it alleges that Spiritâs âquality failures were so severe and persistent that Boeing even placed Spirit on probation for multiple years.â
The lawsuit adds the problems at the company were âwidespreadâ and included âthe routine presence of foreign object debris in Spirit products, missing fasteners, peeling paint, and poor skin quality.â
Seemingly âquality escapeâ on a large scale at Spirit ⊠
The head of the Federal Aviation Administration (FAA) said he believed there were âsignificant problemsâ with the 737-9 Max jet as well as âother manufacturing problemsâ.
The FAA said it would conduct an audit of the planeâs production line.
It also plans to review who is in charge of quality oversight.
For years, the FAA has delegated some parts of quality reviewing of planes to Boeing, but the practice has been controversial, drawing repeated warnings of safety risks.
âIt is time to re-examine the delegation of authority and assess any associated safety risks,â FAA administrator Mike Whitaker said in a statement.
âThe grounding of the 737-9 and the multiple production-related issues identified in recent years require us to look at every option to reduce risk. The FAA is exploring the use of an independent third party to oversee Boeingâs inspections and its quality system.â
Boeing did not immediately comment.
I suspect that any audit will expose multiple transgressions ⊠
I think the first part of this video is of the inside of the plane when after the door fell out. The rest of the video is Daily dose on internet.
US FAA says first 40 inspections of Boeing 737 MAX 9 planes complete
WASHINGTON, Jan 17 (Reuters) - The Federal Aviation Administration (FAA) said on Wednesday that inspections of an initial group of 40 Boeing 737 MAX 9 jets had been completed, a key hurdle to eventually ungrounding the model after a mid-air on Jan. 5.
The FAA had said last week that 40 of 171 grounded planes needed to be re-inspected before the agency would review the results and determine if it is safe to allow the MAX 9s to resume flying following the incident on an eight-week old Alaska Airlines jet.
The FAA said on Wednesday it would âthoroughly review the dataâ and was convening a Corrective Action Review Board before deciding if the planes could resume flights. The agency put no timetable on a decision.
Presumably, out of an abundance of caution.