3 month old 737-9 Max depressurisation incident

[edwin_m]

I have seen (but cannot now find) an image comparing a real door to the fixed panel. The real door has a small round window. The fixed panel has a regular square window. Pictures of N704AL prior to the incident show the square window.

I guess if it had been a real door blocked by an interior panel instead of a fixed external "plug", then Ryanair and all the other carriers using the high density configuration would have been included in the groundings. The edges of the opening looked intact on post-accident pictures, so I suspect the fixed "plug" is attached from the outside, and the internal pressure doesn't act to hold it in place as it would with a genuine plug door.

 

[YorkRailFan]

I guess if it had been a real door blocked by an interior panel instead of a fixed external "plug", then Ryanair and all the other carriers using the high density configuration would have been included in the groundings. The edges of the opening looked intact on post-accident pictures, so I suspect the fixed "plug" is attached from the outside, and the internal pressure doesn't act to hold it in place as it would with a genuine plug door.

Boeing deactivates the door when there is fewer than 190 seats onboard, the high density 737-8-200 with Ryanair has 198 seats so the door is activated.

 

[Brissle Girl]

I agree that it's 99.9% certain to be a manufacturing defect, but no possibility should be ruled out offhand.

Part of the investigation will be to verify that neither Alaska nor their contractors have done any work on that area of the plane.

I don’t disagree, but nothing I have seen is pointing the finger at the airline, thus my comment that the airline isn’t being seen in an adverse light at this stage, which was the comment I was challenging.

Boeing on the other hand…

 

[najaB]

The edges of the opening looked intact on post-accident pictures, so I suspect the fixed "plug" is attached from the outside, and the internal pressure doesn't act to hold it in place as it would with a genuine plug door.

Pure speculation, but if I was designing it, then it would still be a plug but the lip would be a lot narrower since it would only function as an air seal, with the loads being taken by bolts.

Now, if the wrong bolts were used, or they weren't torqued correctly then, after a few flights it could be the case that the loads would be bourne by the air seal, and the thin lip of the panel...

Edit: Quick back of an envelope calculation.

The 737 maintains a cabin altitude of around 8,000ft and the aircraft was passing through 16,000ft when the exit departed.

8,000ft pressure differential is about 11psi.

The exit door is 55*25 inches.

11 * 1,250 = 13,500 lbs, so six tons give or take.

 

[dosxuk]

The design of the door (and the plug) are that it is held in place by the internal pressure at altitude. It slides up and behind fixed hard points on the frame when fixed in place. When fitted with a door, it's only an emergency exit and would slide down and then hinge from the bottom before falling away when opened. When fitted with the plug, it's designed to be secured in the upwards position, so that it can't move down and release (this means that bolts are not securing against the pressure, only against that downwards motion - most discussion is surrounding whether the wrong bolts were used (e.g. too short and not actually securing) or missing entirely.

It is a door but is deactivated by Boeing for Alaska Airlines, most passengers don't even know its a door, Boeing activates this when the seating capacity of the aircraft increases to over 200.

It's not really a door if it can't be opened without serious tooling. It's not just a bit of trim hiding the handle, it's a completely different fabrication that mounts to the door frame that exists in the base fuselage design. "Activating" requires replacing the plug with an actual door and fitting all the required hardware and sensors, as well as modifying the internal layout and trim.

 

[DustyBin]

Yes its a cavity in the fuselage to accommodate a door which is sealed off with a permanent blanking plug, the outline of the plug can be seen from the outside but not the inside where it has regular wall panelling. The cavity is there so only one design of fuselage is required to be built that accommodates both options. The cavity isnt present on -7 fuselages and is always a door on -10 fuselages, on -8 and -9 it is an optional emergency door depending on seating density, *Ryanair has it as a door on its -8's whereas no US carriers at present use it as a door and all have the plug installed instead.

*Easyjet to Ryanair

Just for clarity it’s worth noting that Ryanair has MAX 8-200s; regular MAX 8s don’t have a plug installed as the additional opening isn’t there.

 

[WatcherZero]

The plug inspection the FAA has ordered takes between 4 and 8 hours per plane so its a pretty involved process.

 

[najaB]

Q

The plug inspection the FAA has ordered takes between 4 and 8 hours per plane so its a pretty involved process.

A lot of that will be removing seats and the interior panels and putting them back afterwards.

 

[Enthusiast]

Edit: Quick back of an envelope calculation.

The 737 maintains a cabin altitude of around 8,000ft and the aircraft was passing through 16,000ft when the exit departed.

8,000ft pressure differential is about 11psi.

The exit door is 55*25 inches.

11 * 1,250 = 13,500 lbs, so six tons give or take.

I know it's only back-of-an-envelope, but the 8,000ft equivalent cabin pressure is about 11psi whilst atmospheric pressure at 16,000 feet is about 8psi. So the differential pressure between the cabin and the outside is about 3psi. This makes the load on the door/plug about 1.8 tons.

 

[edwin_m]

This video explains how the plug option is supposed to work and speculates a little on why it might have failed.

 

[najaB]

I know it's only back-of-an-envelope, but the 8,000ft equivalent cabin pressure is about 11psi whilst atmospheric pressure at 16,000 feet is about 8psi.

Ah, I see my mistake. The calculator I used was for the difference between sea level and 8,000.

 

[YorkRailFan]

US investigators have recovered a part of the fuselage that blew out of an Alaska Airlines Boeing 737 Max 9 jet from the backyard of a school teacher in Portland, Oregon.

The National Transportation Safety Board (NTSB), which is investigating the incident, said that the part of the fuselage had been located on Sunday by a school teacher named Bob. He reportedly sent the agency two photos of the wreckage in his backyard.

The federal agency had requested people to keep an eye out for the door plug in the Cedar Hills region, west of Portland.

Earlier on Sunday, a group of local residents searched through a stretch of land full of dense thickets, situated between bustling roads and a light rail train station. According to the Associated Press, a searcher identified as Adam Pirkle said he had ridden 22km, manoeuvring his bicycle through the overgrowth. I’ve been looking at the flight track, "I was looking at the winds,” he said. “I’ve been trying to focus on wooded areas.”

NTSB Chair Jennifer Homendy told reporters on Sunday: “I’m excited to announce that we found the door plug.” She thanked the school teacher, identified by his first name only. “Thank you, Bob.

“We’re going to go pick that up and make sure that we begin analysing it,” Ms Homendy said.

Two cell phones have also been found, one in a yard and another on the side of the road, she added.

It was also reported that Alaska Airlines pilots experienced pressurisation warning lights on three prior flights of a two-month-old Boeing 737 MAX 9 jet before it made an emergency landing due to a torn door plug. Ms Homendy mentioned on Sunday night that the auto pressurisation fail light had activated on 7 December, 3 January, and 4 January. However, she stated that it remained unclear whether there was any connection between those incidents and the rapid depressurisation incident. On Saturday, the Federal Aviation Administration (FAA) issued a directive to temporarily ground 171 Boeing MAX 9 jets equipped with the same panel after the Alaskan Airlines plane had to make an emergency landing due to a gap in the fuselage.

“They heard a bang,” Ms Homendy told reporters on Sunday, of the flight deck crew.

“Communication was a serious issue... It was described as chaos,” she added. It must have been a terrifying event to experience,” Ms Homendy said.

After takeoff from Portland, Oregon, en route to Ontario, California, the door plug on the left side of an Alaska Airlines jet tore off. This incident compelled the pilots to turn back and execute a safe landing, ensuring the well-being of all 171 passengers and six crew members on board.

NTSB also said that the cockpit voice recorder from the Boeing 737 MAX 9 jet was overwritten by the time it was recovered. Ms Homendy said that there was no data available on the cockpit voice recorder after it was sent to NTSB labs because it was not retrieved by the two-hour mark, when recording restarts and previous data is erased.It’s a very chaotic event. The circuit breaker for the CVR (cockpit voice recorder) was not pulled. The maintenance team went out to get it, but it was right at about the two-hour mark,” she added.If that communication is not recorded, that is unfortunately a loss for us and a loss for the FAA and a loss for safety because that information is key not just for our investigation but for improving aviation safety,” she said.

Chunk of door that blew out of Alaska Airlines Boeing found in teacher’s backyard

Door plug on left side of Alaska Airlines jet tears off after takeoff from Portland, Oregon, en route to Ontario, California

www.independent.co.uk

This further pushes the NTSB's request for 25 hour cockpit recording in the US for all aircraft.

 

[YorkRailFan]

New Delhi: Indian airlines have completed precautionary checks of their Boeing 737 MAX planes, the Directorate General of Civil Aviation said. As a precautionary measure, DGCA on 6 January directed all Indian operators with Boeing 737 Max 8 aircraft to check the operation and proper closing of all over wing emergency exits by 7 January. These checks have been satisfactorily performed on the fleet of operational fleet of Boeing 737-8 Max aircraft by Air India Express (4), SpiceJet (8) and Akasa Air (20)," the regulator said on Monday.

On Sunday, Air India Express said it had completed its inspection and that it was in touch with Boeing and regulators for more information on the issue.On Monday, Akasa Air said there were no adverse findings from the inspection of its MAX aircraft. "We can confirm that there are no adverse findings. We can also confirm that there was no disruption to our operations during this time," a spokesperson said.

The development came after images on social media showed Alaska Airlines flight 1282, a Boeing 737-9 MAX, with a large hole in its side and passengers using oxygen masks. The flight returned to Portland, US, shortly after taking off for Ontario, California, on 5 January. The US Federal Aviation Administration later ordered a temporary grounding of more than 170 Boeing B737-9 MAX aircraft for inspection.

While the aircraft involved in Alaska incident was a Boeing 737-9, the DGCA directed all Indian airlines to conduct a one-time inspection of the emergency exits on all their Boeing 737-8 MAX aircraft out of an abundance of caution. It is important to note that no Indian airline currently operates a Boeing 737-9 MAX. Akasa Air's fleet includes one B737-8200 aircraft which has a mid-cabin door on which the operational check has also been completed satisfactorily," the regulator added.

Indian airlines have completed checks of Boeing 737 MAX planes, says DGCA

The regulator ordered the emergency inspection after images on social media last week showed Alaska Airlines flight 1282, a Boeing 737-9 MAX, with a large hole in its side and passengers using oxygen masks.

www.livemint.com

I'm more interested as to if Ryanair is conducting inspections of their 737-8-200s or not, but this is still a positive story.

 

[Lost property]

The plug inspection the FAA has ordered takes between 4 and 8 hours per plane so its a pretty involved process.

it's called an A.D. (Airworthiness Directive)

" A lot of that will be removing seats and the interior panels and putting them back afterwards "

No, sorry, that's not the case. Seats can be removed in a matter of minutes, likewise re-fitted. Cabin trim, which is a nightmare / PITA, can take a bit longer unless the operator utilises the skills of cabin trimmers, worth their weight in gold I assure you as they specialise in cabin interiors / fits and certainly for VVIP / VIP configurations.

The time will be taken up doing the initial inspection, by whatever form for the A.D stipulates, any rectification required, and then a further duplicate inspection plus, in all probability, an engine ground run and pressurisation check.

 

[Towers]

Real door
View attachment 149820

Presumably then on the door fitted variant some poor sod gets a ‘window’ seat with no window?!

 

[Tetchytyke]

Presumably then on the door fitted variant some poor sod gets a ‘window’ seat with no window?!

Yes, and anyone who complains on Twitter/X will receive a withering putdown from Ryanair.

I don’t disagree, but nothing I have seen is pointing the finger at the airline, thus my comment that the airline isn’t being seen in an adverse light at this stage, which was the comment I was challenging.

Boeing on the other hand…

It has been reported that the pressurisation error light had lit on several occasions in the last few weeks on that aircraft, that the aircraft was banned from flying over water as a result, and that Alaska had not investigated it properly by the time the plug eventually failed.

Alaska Airlines plane had warnings days before mid-air blowout

The jet involved in Friday's incident had been prevented from long trips over water, US investigators say.

www.bbc.co.uk

Speaking at a news conference, Ms Homendy said pilots reported pressurisation warning lights on three previous flights made by the specific Alaska Max 9 involved in the incident.
The decision to restrict lengthy flights over water was so that the plane "could return very quickly to an airport" in the event the warnings happened again, the NTSB chief added.
It is not clear if there is a link between the issues that led to those warnings, and the issue that caused the blowout on 5 January.
The plane was brand new having been delivered to Alaska Airlines in October - at which time it was judged by the FAA to be airworthy.

That was after Alaska had a load of their aircraft grounded by the FAA a few weeks ago for emergency inspections.

I'm going to go with manufacturing or assembly defect by Boeing which should have been picked up and addressed by Alaska, but wasn't.

 

[mpthomson]

Yes, and anyone who complains on Twitter/X will receive a withering putdown from Ryanair.

It has been reported that the pressurisation error light had lit on several occasions in the last few weeks on that aircraft, that the aircraft was banned from flying over water as a result, and that Alaska had not investigated it properly by the time the plug eventually failed.

Alaska Airlines plane had warnings days before mid-air blowout

The jet involved in Friday's incident had been prevented from long trips over water, US investigators say.

www.bbc.co.uk

That was after Alaska had a load of their aircraft grounded by the FAA a few weeks ago for emergency inspections.

I'm going to go with manufacturing or assembly defect by Boeing which should have been picked up and addressed by Alaska, but wasn't.

That's how I see it as well. Alaska may not come out of this all that well.

 

[Brissle Girl]

Yes, I agree that the case against Alaska is somewhat stronger given the evidence emerging of the previous pressurisation warnings.

Presumably though the previous groundings were the result of the general alert for the loose bolts issue, rather than something specific to the Alaska fleet?

 

[edwin_m]

Somewhat worrying that it's now been reported the incident blew the cockpit door open, at least one checklist and the first officer's headphones ending up in the cabin. I thought these doors were supposed to be impenetrable?

 

[WatcherZero]

Presumably then on the door fitted variant some poor sod gets a ‘window’ seat with no window?!

Yes the 'Deactivated' variant they fit an emergency door but panel it over so you get a seat with no window. Then there is a couple of variations with the door active with sub variations by size of seats but primarily with an unsupervised door which is illegal in Europe or a door with a cabin attendant seat facing backwards installed in the row in front. The doors have interlocks which is slaved to the thrust controls and a locking bolt engages when the thrust lever is set to 58 degrees or higher and disengages when it isnt so they can only be opened (say by a rogue passenger) on the ground or during a landing.

Cockpit audio recorder data was lost as it only has a two hour capacity and is continually recorded over and no one thought to disconnect it from power so when it was retrieved just over two hours after landing the final data had just been overwritten (Airbus planes since 2021 have a 25 hour tape).
Three pressurisation warnings had occurred, once a month previous then in the two days before the accident, one time in the air and at least once on the ground. Each time the fault had been cleared and correct pressure achieved and the warnings in themselves are not that uncommon usually just bad seals.

Somewhat worrying that it's now been reported the incident blew the cockpit door open, at least one checklist and the first officer's headphones ending up in the cabin. I thought these doors were supposed to be impenetrable?

They are armoured but an armoured door can still be blown off, the depressurisation differential at the low altitude the plane was flying at was the equivalent of a ton and half of force on the area of a door, if it had been at cruising altitude it would have been two and half tons of force.

 

[YorkRailFan]

Emergency Airworthiness Directive (AD) 2024-02-51 is sent to owners and operators of The
Boeing Company Model 737-9 airplanes.
Background
This emergency AD was prompted by a report of an in-flight departure of a mid cabin door
plug, which resulted in a rapid decompression of the airplane. The FAA is issuing this AD to address
the potential in-flight loss of a mid cabin door plug, which could result in injury to passengers and
crew, the door impacting the airplane, and/or loss of control of the airplane.
FAA’s Determination
The FAA is issuing this AD because the agency has determined the unsafe condition
described previously is likely to exist or develop in other products of the same type design.
AD Requirements
This AD prohibits further flight of affected airplanes, until the airplane is inspected and all
applicable corrective actions have been performed using a method approved by the Manager,
AIR-520, Continued Operational Safety Branch, FAA.
Interim Action
The FAA considers this AD to be an interim action. If final action is later identified, the FAA
might consider further rulemaking then.
Authority for this Rulemaking
Title 49 of the United States Code specifies the FAA’s authority to issue rules on aviation
safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII,
Aviation Programs, describes in more detail the scope of the Agency’s authority.
The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A,
Subpart III, Section 44701, General requirements. Under that section, Congress charges the FAA
with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices,
methods, and procedures the Administrator finds necessary for safety in air commerce. This
regulation is within the scope of that authority because it addresses an unsafe condition that is likely
to exist or develop on products identified in this rulemaking action.


2
Presentation of the Actual AD
The FAA is issuing this AD under 49 U.S.C. Section 44701 according to the authority
delegated to me by the Administrator.
2024-02-51 The Boeing Company: Project Identifier AD-2024-00021-T.
(a) Effective Date
This emergency AD is effective upon receipt.
(b) Affected ADs
None.
(c) Applicability
This AD applies to The Boeing Company Model 737-9 airplanes, certificated in any category,
with a mid cabin door plug installed.
(d) Subject
Air Transport Association (ATA) of America Code 52, Doors.
(e) Unsafe Condition
This emergency AD was prompted by a report of an in-flight departure of a mid cabin door
plug, which resulted in a rapid decompression of the airplane. The FAA is issuing this AD to address
the potential in-flight loss of a mid cabin door plug, which could result in injury to passengers and
crew, the door impacting the airplane, and/or loss of control of the airplane.
(f) Compliance
Comply with this emergency AD within the compliance times specified, unless already done.
(g) Inspection or Other Action
As of receipt of this emergency AD, further flight is prohibited until the airplane is inspected
and all applicable corrective actions have been performed using a method approved by the Manager,
AIR-520, Continued Operational Safety Branch, FAA.
(h) Special Flight Permits
Special flight permits, as described in 14 CFR 21.197 and 21.199, are allowed only for
unpressurized flights.
(i) Alternative Methods of Compliance (AMOCs)
(1) The Manager, AIR-520, Continued Operational Safety Branch, FAA, has the authority to
approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In
accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight
Standards District Office, as appropriate. If sending information directly to the manager of the


3
certification office, send it to the attention of the person identified in paragraph (j) of this AD.
Information may be emailed to: [email protected].
(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking
a principal inspector, the manager of the local flight standards district office/certificate holding
district office.
(3) An AMOC that provides an acceptable level of safety may be used for any repair,
modification, or alteration required by this AD if it is approved by The Boeing Company
Organization Designation Authorization (ODA) that has been authorized by the Manager, AIR-520,
Continued Operational Safety Branch, FAA, to make those findings. To be approved, the repair
method, modification deviation, or alteration deviation must meet the certification basis of the
airplane, and the approval must specifically refer to this AD.
(j) Related Information
For further information about this AD, contact Michael Linegang, Manager, Operational
Safety Branch, FAA; phone: 817-222-5390; email: [email protected].
Issued on January 6, 2024.
Caitlin Locke, Director,
Compliance & Airworthiness Division,
Aircraft Certification Service.

Dynamic Regulatory System

drs.faa.gov

AD from the FAA above, this has also been adopted by EASA.

 

[YorkRailFan]

DUBAI - Airline flydubai said on Sunday that the three Boeing 737 MAX 9 planes in its fleet were not affected, after U.S. regulators temporarily grounded 171 Boeing 737 MAX 9 jetliners for safety checks, the United Arab Emirates carrier told Dubai-based Khaleej Times newspaper.

"Following The Emergency Airworthiness Directive (EAD) issued by the Federal Aviation Administration (FAA) on January 6, 2024, we can confirm that the three Boeing 737 MAX 9 aircraft in our fleet are not affected," a flydubai spokesperson told the newspaper.

"Flydubai operates Boeing 737 MAX 9 aircraft with a deactivated mid-aft exit door configuration, which is not referenced in the directive."

Airline flydubai says its three BOEING 737 MAX 9 unaffected by FAA grounding - Khaleej Times

Flydubai operates Boeing 737 MAX 9 aircraft with a deactivated mid-aft exit door configuration

www.zawya.com

I find this statement concerning. The DGCA has ordered a full inspection of all 737 MAX aircraft in India, yet no Indian carrier operates the 737-9 (Akasa operates the 737-8-200), in the interest of safety. Yet FlyDubai is not inspecting their 737-9s, as the saying goes "Better to be Safe than Sorry".

 

[westcoaster]

Something interesting was posted on airliners.net

The aircraft in question spent 10 days at a maintenance facility to have the WiFi bubble on the roof and the internal gubbins fitted ( WiFi antenna (bubble my words)).

This is above the area where the plug is situated. First pressurisation issue was the day it was released from the maintenance facility.

AS1282 PDX-ONT decompression event, returned to PDX, FAA temporarily grounds 737MAX9 for inspections - Page 18 - Airliners.net

Quote WkndWanderer

Alaska’s MRO vendor is AAR at OKC, the plane spent ten days there from 11/27-12/7 based on its flight history. The NTSB chair in tonight’s briefing stated that the first pressure warning indication occurred on 12/7…which would be the exact day the aircraft returned to regular service after its visit there. Another poster has stated that WiFi installations are done at the AAR facility, and pointed out that the mod goes right over the same area where the plugs are located. Does anyone know if these are usually opened during the WiFi install?

https://www.flightaware.com/live/flight ... istory/160

https://www.aarcorp.com/en/newsroom/pre ... homa-city/

 

[YorkRailFan]

Team,

As we work diligently with our regulators and support our customers following the Alaska Airlines Flight 1282 in-flight incident, I will hold a company-wide webcast on safety on Tuesday Jan 9, from Renton, joined by several members of our executive leadership team.

When it comes to the safety of our products and services, every decision and every action matters. And when serious accidents like this occur, it is critical for us to work transparently with our customers and regulators to understand and address the causes of this event, and to ensure they don't happen again. This is and must be the focus of our team right now, I am deeply grateful to our colleagues who have been working tirelessly on our company's response over the past two days

We will spend time together Tuesday talking about our company's response to this accident, and reinforcing our focus on and our commitment to safety, quality, integrity and transparency. While we've made progress in strengthening our safety management and quality control systems and processes in the last few years, situations like this are a reminder that we must remain focused on continuing to improve every day.

Further details about the webcast will be shared with all employees on Monday via email and BNN.

Thank You,
Dave

This email has been shared with Seattle Times Journalist Dominic Gates and is viewable here

Jan 8 (Reuters) -Icelandair ICEAIR.IC said on Monday it is not affected by the U.S. Federal Aviation Administration's temporary grounding of some Boeing BA.N 737 MAX 9 planes, after a jet operated by Alaska Airlines ALK.N suffered a plug door blowout during a flight on Friday.

"It has been confirmed that the issue is related to equipment that is not a part of Icelandair's Boeing 737 MAX 9 configuration," a spokesperson of the airline, which operates four such aircraft, told Reuters.

Icelandair says it is not affected by FAA's MAX 9 groundings

The XM Research Desk, manned by market expert professionals, provides live daily updates on all the major events of the global markets in the form of market reviews, forex news, technical analysis, investment topics, daily outlook and daily videos.

www.xm.com

Very similar to FlyDubai's statement posted up-thread.

 

[najaB]

No, sorry, that's not the case. Seats can be removed in a matter of minutes, likewise re-fitted. Cabin trim, which is a nightmare / PITA, can take a bit longer unless the operator utilises the skills of cabin trimmers

Thing is, "a lot" isn't a specific number, by the way.

Even if it only takes ten minutes to remove the seats and trim panel and the same to put them back (not an unrealistic number given that cabin trim is, in your own words, a "PITA" and some operators now have IFE in their narrow bodies) that's still twenty minutes per-side or 40 minutes overall. I think that 40 minutes out of a two-hour job meets the broad definition of "at lot".

 

[GB]

deleted

 

[WatcherZero]

Shouldnt be opened during the Wi-Fi installation, for all intents and purposes the plug is the external fuselage with 4 locking bolts over the four door runners so it cannot move and a couple of spring loaded pivoting arms at the bottom, there are no wiring looms or sensors running to the plug.

 

[GB]

Door diagram

 

[Bletchleyite]

Seems a flawed design. Why would one not have it so it was plugged from inside and thus the pressure would hold it closed?

There is quite a history of outward opening doors causing trouble.

 

[edwin_m]

Seems a flawed design. Why would one not have it so it was plugged from inside and thus the pressure would hold it closed?

There is quite a history of outward opening doors causing trouble.

From previous posts and the video linked above, I think it is normally held by internal pressure but when it is lowered, the parts that retain it are no longer aligned so it opens outwards. For the plug option, four bolts are fitted to stop it lowering unless needed during maintenance.