0:00

I'm Dr Carl, coming to you from

0:02

the lands of the Gadigal people of

0:04

the Eora nation. I acknowledge Aboriginal and

0:06

Torres Strait Islander peoples as the first

0:09

Australians and traditional custodians of the lands

0:11

where we live, learn and work. G'day

0:15

Dr Carl, Shirtloads of Science University of Sydney,

0:18

talking with Dr Sonia Brown. Thanks

0:20

Dr Carl. And you're a lecturer

0:22

at the University of New South

0:24

Wales. Correct. And your field is?

0:27

Airspace Design. And a few airplanes have

0:29

been doing bad things recently. We're talking

0:31

now in early 2024. And

0:34

the Alaska Airlines airplane was

0:36

a 737. Now the

0:39

737, it's been around for about

0:41

half a century. Is that right? Yeah, it's been

0:43

around for over 50 years. The original 737s came out in

0:45

the 60s. Oh

0:48

my God. So it went through the 737 original,

0:52

then the classic, then the next generation. Now we've

0:54

got the MAX. And Alaska

0:56

Airlines ones, what model was that? A

0:59

Boeing 737 MAX 9. And

1:02

it was a plug for an

1:04

additional optional emergency exit door. Why

1:07

would you have an emergency exit door optional? Like

1:09

if when I go into a chemist I don't

1:11

say, oh can I just have the average grade?

1:14

I want the full maximum. So why don't they

1:16

have the full maximum number of emergency doors? On

1:19

aircraft the amount of emergency exits you need is based

1:21

on the number of people you're carrying because you need

1:23

to be able to get them all off an emergency,

1:25

which needs to be certified to 90 seconds.

1:28

With particular aircraft you can certify them to

1:31

a maximum number of people, but certain airlines

1:33

will choose to carry less than that. For

1:35

example, 737 MAX 9 is

1:37

certified to carry over 200 people maximum. However,

1:42

if an airline wants to run a

1:44

dual class configuration, so say a spacious

1:46

business area up the front, and then

1:48

a small economy section it might be carrying less than

1:50

200 people, so it

1:53

may not need the extra emergency exits.

1:55

And therefore because of weight reasons and

1:57

complexity reasons, they'll replace it with this.

2:00

plug. It's just an aluminium plug

2:02

in the door. The emergency exit

2:04

door itself weighs a lot more because it

2:06

has to have all the features to actually

2:08

be able to open out in emergency plus

2:10

all the emergency systems. So for example, extra

2:13

emergency exit slides that have to be able

2:15

to deploy from there. You'd also have to

2:17

have those seats spaced further apart of that

2:19

location to have that emergency exit aisle as

2:22

well. It is actually significant for the airlines

2:24

if they don't want to carry that amount

2:26

of people to be having that whole extra

2:28

systems two times out on both sides of the

2:30

aircraft. I had no idea that they would put a

2:32

plug in the side of the 737. How long have

2:35

they been doing this offering various versions of the 737

2:37

which is one of the most popular

2:39

light jets ever made, isn't it? There's

2:41

thousands of 737s out there. The plug that is on

2:44

the 737

2:46

MAX 9, a very similar plug was also

2:49

used in the next gen series of aircraft.

2:51

So there was the Boeing 737-900ER which was

2:53

introduced in around 2007 which also has variants

2:55

which include

3:00

this plug. So these have been flying for

3:02

over a decade, 15 years or so. In

3:05

this case, the door popped when

3:08

it got to 60,000 feet. Does

3:10

the fact that the door popped halfway

3:13

to maximum altitude so it wasn't full pressure

3:15

difference between the inside and the outside, does

3:17

that give you any hints as to what

3:19

might be going on? It does

3:21

at 16,000 feet. We note that

3:24

inside the aircraft typically we pressurised

3:26

to around 8,000 feet.

3:28

So somewhere in the 6 to 8,000 feet but we assume

3:30

8,000 feet. That means our

3:33

pressure difference at that point was around 20,000 kilopascals

3:36

whereas to the maximum certified altitude,

3:39

it's almost three times that pressure difference.

3:41

So the fact that it has come

3:43

off so early

3:45

indicates that there's probably

3:47

something physically wrong. So

3:50

either something went

3:52

wrong in manufacturer installation or potentially

3:54

there's been damage to it since

3:56

it's been in service that hasn't been detected rather

3:59

than I guess what would be most scary

4:01

or critical which would be an actual design issue.

4:04

It's wonderful listening to your engineer brain

4:06

work through the different possibilities and

4:09

kind of put down at

4:11

the bottom of the list a design

4:13

problem because it's been flying for so

4:15

long. You casually mentioned 90 seconds.

4:17

I keep on reading about this and I've read

4:19

in Aviation Week of Space Technology that what they

4:21

do when they want to certify a plane for

4:24

96 and they'll actually prove it can be done.

4:26

They get all the cabin crew, they train them

4:28

up, they pick all the skinny ones and then

4:30

they say go and they can get all of

4:32

them out in 90 seconds. But let's go

4:34

back to the I think it was

4:36

the first of January when there was

4:39

a collision between two planes at a

4:41

airport in Japan or was it two places? It

4:44

was a Japan Airlines Airbus A350.

4:46

So this is a big

4:48

plane twin aisle as compared

4:50

to single aisle and a

4:52

Coast Guard Bombardier Dush 8.

4:55

It took more than 90 seconds and there

4:57

was a report of some person slowing people

5:00

down by reaching up and then grabbing his

5:02

bag over had been and then putting it

5:04

on the slide and then tearing the

5:06

slide on the way down. So the 90

5:09

seconds is the optimal situation is what we

5:11

certify for but it does assume

5:13

that everything is operating as expected

5:15

which also includes things like all

5:17

of the exits and all of

5:19

the slides operating. So in the

5:21

case of the Airbus A350 it's

5:24

fitted with eight emergency exits

5:26

and eight emergency slides. My

5:29

understanding is they only had

5:31

three emergency exits and emergency slides

5:34

operating for that evacuation. So that

5:36

does obviously make it take

5:38

significantly longer which is why

5:40

in design also we want to make

5:42

sure that when there is an emergency exit as

5:44

long as possible is available which as I say

5:47

thankfully for the Japan Airlines case everyone got off

5:49

safely. Both the forward

5:51

door and the rear door near the

5:53

tail were operating on the side where

5:56

the wing was damaged and on

5:58

the other side which wasn't

6:00

where the damage was, only the

6:02

aftmost, only the one near the tail was

6:05

operating. So they didn't operate on either side

6:07

near the wings, obviously on the case where

6:10

the damage is. My understanding is

6:12

they also didn't operate the front doors

6:14

on the side where the damage wasn't

6:17

because they some reports that

6:19

I haven't been able to confirm that

6:21

engine was not shut down properly. So

6:24

you can't have people evacuating out in

6:26

front of an engine that is not

6:28

fully shut down. And if people get sucked into

6:30

an engine that's very bad. That would be very

6:33

bad. On an aeroplane, how

6:35

much attention do you play to the flight crew because what

6:37

I do is I stare at them

6:39

and I give them a little wave at the beginning and then

6:42

that way I know they know I'm paying attention

6:44

because I feel so sorry for them when people

6:46

ignore them. Because I know that in

6:48

an emergency, I discovered this in medicine,

6:51

in an emergency you drop to

6:53

your lowest level of training. And

6:56

so on one hand I've seen the photo

6:58

of people on the

7:00

wing of the A320 that landed

7:03

in the Hudson River and they're standing on the

7:05

wing and they're all wearing their life jackets inflated

7:08

and about three-quarters have got them inflated wrongly. They

7:10

haven't paid attention. Some of them are up in

7:12

the air above their head. I haven't

7:15

done the place the strap around your waist and

7:17

clip it tightly and pull on the strap to

7:19

tighten. They've missed that bit. Yeah so I

7:21

always firstly wave to them then pay attention

7:24

firstly because they will look after me I

7:26

hope if things go bad and then secondly

7:28

as an act of solidarity with a fellow

7:30

professional performer because I feel sorry for the

7:33

people not paying attention. You've probably memorized all

7:35

this stuff anyway though. I've pretty much got

7:37

it memorized in my head but I'm certainly always

7:39

looking at them and making sure I am

7:41

aware of where I'm seated relative to

7:43

those exits. And I think

7:46

one of the most important things that

7:48

the flight attendants say is

7:50

in the case of a loss of pressure

7:53

which we had already on the Boeing 737

7:55

MAX 9. When those

7:58

masks come down you should fit your own mask

8:00

first before helping other people including

8:02

children. Now as a parent myself

8:05

it's a conflict right the thing you most care

8:07

about is your child but the reason they say

8:10

that is because in the event of a loss

8:12

of pressure depending obviously on the altitude without

8:14

oxygen yourself you can lose consciousness and

8:16

then you can't help yourself or your

8:18

child. So it's actually one of

8:20

the most important things they say is fit your

8:23

own mask first. Order

8:25

is important and listening to the flight

8:27

crew in those situations and as

8:29

quickly as you can safely. We've

8:32

talked about two sets

8:35

of airplane bad things the

8:37

Airbus 380 and the 737 then

8:40

we had a bit of what

8:42

looked like a design problem stuck

8:44

through in the first of the

8:46

max theories where according

8:49

to various articles I've written in New

8:51

York Times and Aviation Week in Space

8:53

Technology there was a conflict between the

8:55

engineers and the bean counters or the

8:58

accountants in the company and in this

9:00

case the summary is I guess that

9:02

the bean counters one and two planes

9:05

crashed. I'm not sure

9:07

I want to you know go labeling

9:09

blame within Boeing on this

9:11

one but the big design fault

9:13

in this case was that they

9:16

had an angle of

9:18

attack sensor which basically monitors

9:20

the angle of the aircraft

9:23

relative to the oncoming air flow. It's like a

9:25

little flippy thing that sticks out the side and if

9:27

the wind is running parallel to the

9:30

length of the airplane it'll be dead flat

9:32

and it can swivel around up and down

9:34

depending on if the airflow is going from

9:36

top to bottom or bottom to top or

9:38

just along the fuselage it swivels around. Yeah

9:40

so they had multiple of the sensors

9:42

but they had one of these sensors

9:44

that was providing input to a particularly

9:46

new system that they installed which

9:49

has a really long

9:51

complicated name called the Maneuvering

9:54

Characteristics Augmentation System MCAS

9:56

but basically it means an anti-stall system

9:59

so what it was to do was

10:01

detect if that angle of attack became

10:03

too high due to drift

10:05

over time that maybe the pilots didn't notice

10:07

and then push the nose down in that

10:09

case. That was what it was designed to

10:11

but one of the issues with the

10:14

system was that it was just reading off of one

10:16

sensor. There's two sensors and they deliberately

10:19

ran only off one and I read a

10:21

report by an engineer who said he tried

10:23

to get them to read off both

10:25

and have it what he called a

10:27

synthetic airspeed system but his bosses wouldn't

10:29

let him do it. I don't know

10:31

about the internal decisions there

10:33

but unfortunately what went

10:35

live was reading off of one

10:37

sensor which is basically a no-no. Because you got

10:39

no redundancy. Actually we should just back up a

10:42

bit here. So what had happened was that they

10:44

had the series the first ones in the classics

10:46

and the next gen they went for the max

10:49

and they were limited by how big an engine they

10:51

could put on it and Airbus was coming out with

10:53

new designs and it was easy for them to put

10:55

on a new bigger engine because they

10:57

were working from scratch but here they're putting on a

11:00

new engine on a 50-year-old plane and it

11:02

was so big they decided to mount it

11:04

more forward and more up. So

11:07

it changed the stability characteristics so

11:09

that's why they thought it might

11:11

gradually drift up because the stability

11:13

profile of the max was different

11:16

to those particularly those next-gen aircraft

11:18

that it was building off of. By the age

11:20

of a bit of background which I never realised

11:22

before reading all this and airplane normally flies a

11:24

couple of degrees nose up. Ideally

11:27

mostly in cruise we

11:29

would want the fuselage to be mostly

11:31

horizontal however the wing should

11:33

be set at what we call an

11:35

incidence angle so the wing will be

11:38

slightly up relative to the fuselage to

11:40

produce the lift required for cruise. So

11:42

I was wrong when I gave the information

11:44

that they're tilted up by a degree or

11:46

so with the whole airplane. The air is

11:49

running parallel to the fuselage. Ideally

11:51

for minimum drag we'd want it

11:53

parallel but to do that and

11:55

to still get the lift required our

11:57

wing will be tilted effectively a little.

12:00

bit. The entire wing on installation,

12:03

on installation, it will have an angle relative

12:05

to the fuse large which is called an

12:07

incidence angle. I kind of love talk to engineers

12:09

who tell me where I'm wrong and get me

12:11

started on getting things right. So with the Mac

12:14

the engine was mounted higher, it

12:17

was a bigger more powerful engine, it was mounted more

12:19

forward and higher and it led to a

12:22

possible tendency for the nose to come up

12:24

and so they put in some software to

12:27

bring the nose down and didn't

12:29

tell the pilots about it, didn't make

12:31

it part of the training. Yeah so

12:33

it wasn't part of any of the

12:35

original training, apparently in the

12:38

original manuals there was something that

12:40

defined the term MCAS to say

12:42

the MCAS equals maneuvering characteristics augmentation

12:44

system but that was the only mention.

12:46

Articles that I read and I could

12:48

be wrong on this implied that Boeing

12:51

wanted pilots who trained on previous 737s

12:53

to be able to walk into this

12:55

one and not do any extra training.

12:58

Well it was a very limited training

13:00

like on an iPad training rather than

13:02

full simulator training. Right, some of the

13:04

engineers were saying maybe

13:06

they should have gone through recertification training

13:09

to handle this MCAS system. It certainly

13:11

would have helped but the problem

13:13

that we had with the Macs back

13:15

then and noting that obviously the system's

13:18

been updated since the incident

13:20

in 2018 and 2019 even

13:23

after the first incident which was lying

13:25

there. Boeing then put out

13:27

a bulletin which outlined

13:29

the system said what you should do if

13:32

it played up and

13:34

the Ethiopian pilots when

13:36

this happened to them, the second

13:38

plane in March 2019, they

13:41

tried to follow that process. It was

13:43

very clear they tried to follow the

13:45

process of Boeing outline so I don't

13:47

think even originally just training was sufficient.

13:50

There were design faults which I say

13:52

now have been addressed thankfully but should

13:54

have been addressed from the get-go. So

13:57

now if those sensors differ by more than

13:59

five... five and a half degrees, the

14:02

MCAD system won't activate. It

14:04

fully cuts it out. It now reads

14:06

from both angle of attack sensors and

14:09

importantly checks the difference between them. So

14:11

in the Ethiopian case at least, it

14:13

was reading off one and that sensor

14:16

read something like 75 degrees, it

14:18

was clearly an erroneous reading. So

14:20

now because it reads off two, it checks them. And

14:23

if the difference is more than five and a

14:25

half degrees, it basically describes them

14:27

both and the system will not activate. The

14:30

other important thing is even if

14:32

they both said it was wrong,

14:35

it now won't activate repeatedly off

14:37

a single elevated reading. So again,

14:39

when it happened, it

14:41

kept reading that it was

14:43

like 75 degrees or whatever it was. So even

14:45

if they both read a number, which meant the

14:48

system would normally activate, if the

14:50

pilots have corrected for it,

14:52

it won't keep activating repeatedly, which it did

14:55

in both the Lion Air and the Ethiopian

14:57

case. And then the other

14:59

thing they did is they reduced control

15:01

authority of that MCAS system.

15:03

Because again, the Ethiopian case,

15:05

it was really clear, both the

15:08

pilot and the co-pilot were pulling back, which just

15:10

basically meant they were trying to use the elevator.

15:13

So the elevator also changes the pitch of the

15:15

aircraft. Is the elevator the flappy thing on the

15:17

back of the wings? It's on the back of

15:19

the tail. Oh, so there was one

15:22

way at the back of the airplane. Is it also

15:24

called a stabilizer? At

15:26

the back, we have the horizontal

15:28

stabilizer, which in the 737 is

15:30

an all-moving stabilizer. So that's what

15:32

the MCAS was controlling this stabilizer.

15:34

So it's technically set

15:36

at an angle, and it kind

15:38

of stays there, but it can move

15:40

small amounts. The front of the wing

15:42

of that stabilizer elevator thing, either up

15:44

or down, but you're implying that it

15:46

can also have one side up and

15:48

one side down. So if you were

15:50

thinking of the horizontal tail of an

15:52

aircraft. Yep, the horizontal bit, not the

15:54

vertical, the

15:56

horizontal bit. The first two thirds

15:58

of that, right? think of that as a

16:01

six part but that's standard

16:19

pitch control so the standard pitch

16:21

control the pilots would use would

16:23

be the elevator the all moving

16:25

horizontal tail or the all moving

16:27

stabilizer that's the front bit and

16:29

that would normally be set to position

16:32

what we call is trim the aircraft basically

16:35

make it stable in straight and level flight

16:37

so it would move that so that we

16:39

have to have minimum control inputs when

16:41

we're in straight and level flight basically

16:44

balance what we call the moments on

16:46

the aircraft. Now what

16:48

do you call the flappy things on the backs of

16:50

the big wing? Inboard will

16:52

have flaps and outboard

16:54

will have ailerons. Oh so neither of

16:56

them are called elevators? No elevators are only on

16:58

the tail. I've also heard the word flaperon. Flaperon

17:01

is basically a cross between a flap

17:03

and an aileron so there's elevons for

17:05

example which is a cross between an

17:08

elevator and an aileron so it depends

17:10

on the control but the most basic

17:12

controls we have is on

17:14

the tail the flappy bit at the back of

17:16

the elevator and on the wing the

17:18

flappy bits of the back inboard is

17:21

our flaps and outboard

17:23

is ailerons but as I say there

17:25

are combinations which have funny names like

17:27

elevons or flaperons etc. Are

17:30

you happy to fly in airplanes

17:32

in general do you think there's still a safe

17:34

way of transport? Flying is the safest

17:36

mode of transport we have not only

17:39

am I happy to fly and fly when

17:41

I can I happen to live under a

17:43

flight path. You're afraid of your flight path you

17:45

can see them dangle at Dunlops as they come over you?

17:47

I think that's a little after me I don't think

17:49

I'm quite that close to the airport but I

17:51

do get to watch the planes come over sometime

17:53

which is nice. How can people follow you and

17:55

you'll find work or if they want to become

17:57

a student of yours do you take students? Yes,

18:00

I take students. I take research students. They

18:02

can just look me up, Sonia Brown at

18:04

UNSW or if anyone wants to follow me,

18:06

they can look me up on LinkedIn. I

18:09

don't know why, but for a long time I've believed,

18:11

but wrongly it turns out that the fuselage

18:13

was slightly tipped up. I

18:16

didn't think it through a course or not

18:18

because you want to get dragged. You just

18:20

tip the wings up slightly, the fixed wings.

18:22

Thank you very much Dr. Sonia. Thanks Dr.

18:24

Carl. Shirtloads of science is washed, spun and

18:26

aired by the University of Sydney.