Original subtitles

(aircraft droning)

- (yells) What have we done? - (yells) I don't know, mate! I don't know.

NARRATOR: The pilots of a turboprop airliner

face a nightmare situation over Papua New Guinea.

Mayday, mayday, mayday.

(radio) Double engine failure and we're making an emergency landing.

DI GIULIO: This crew lose both engines at the same time.

There is only really one outcome.

(suspenseful music)

(metallic screeching)

NARRATOR: Investigators quickly discover clues in the wreckage.

Landing gear's up.

- INVESTIGATOR 2: The flaps are up too. - They weren't configured for landing.

NARRATOR: Something in the cockpit voice recording…

Amplify what's left.

BLANKENSTEIN: Well, there it is.

NARRATOR: …reveals a potentially deadly flaw in an aircraft used around the world.

We wanted to make sure that the thousand aircraft that were out there

were operating safely. (plane droning)

PILOT: Mayday. Mayday.

GPWS: Pull up!

(indistinct radio chatter)

(indistinct radio chatter)

NARRATOR: Airlines PNG Flight 1600 soars 16,000 feet

above Papua New Guinea's Finisterre Mountain Range.

We're at cruise.

NARRATOR: Australian Captain Bill Spencer is an experienced flight commander.

Cruise power is set.

NARRATOR: New Zealander Campbell Wagstaff is the first officer

on today's late afternoon flight.

Both pilots were with PNG for about a year.

The captain had very good experience. He had about 18,000 hours of flying time.

The first officer was also very experienced

with just shy of 3,000 hours flying experience himself.

(indistinct low chatter)

NARRATOR: One flight attendant looks after the comfort

and safety of the 29 passengers on board.

Most are parents heading to their children's graduation

at Divine Word University at Madang.

PNG Flight 1600 is midway into a 30 minute flight

to the town of Madang on Papua New Guinea's north coast.

- How's the arrival time looking? - Seventeen after the hour. Right on time.

NARRATOR: The pilots are flying manually today

because their autopilot is inoperative.

They're at the controls of a twin-engine Bombardier Dash 8,

well suited to carrying passengers around the Pacific Island.

DI GIULIO: The airplane is able to operate in and out of short runways,

unprepared runways oftentimes, in smaller communities where the facilities required

to operate a larger passenger aircraft wouldn't be available.

(engines roar)

NARRATOR: Two Pratt and Whitney turboprop engines power a plane

that's nearly 23 years old.

DI GIULIO: The Dash 8 is one of these airplanes that's become timeless.

It's still operated by airlines all over the world.

As some of the major airlines upgrade their airplanes

to more modern jet aircraft,

the Dash 8s find a new home with other airlines

because they're always in high demand.

PILOT (radio): Charlie Bravo nearing Madang. We're coming through it.

- You hear that? - Mm-hmm.

NARRATOR: Forty miles from Madang, the pilots get an update on the weather ahead.

A storm is building near their destination.

- I'll take us around it, alright? - Good idea.

Turboprop aircraft cannot fly as high as a jet airliner can,

which means they can't go over a lot of the weather

they may experience on their flight.

Madang Tower, Airlines PNG 1600. We're diverting slightly to avoid weather.

PNG 1600, Madang Tower. Diverting, copy.

NARRATOR: Captain Spencer navigates around the storm.

(aircraft drones)

MCNAIR: The captain's trying to avoid clouds, which is normal.

You want to give your passengers a smooth ride.

NARRATOR: But 38 miles from Madang, the crew still can't see the airfield.

- I'm gonna take us down. - Copy.

DI GIULIO: At a major airport,

there are typically procedures in place that we can fly

that will bring us through the clouds and point it right at the runway.

Oftentimes, at more remote airports, these procedures do not exist,

so we have to descend below a layer of clouds.

Once you're below a layer of cloud,

you can visually navigate to an airport and conduct a safe approach and landing.

NARRATOR: The crew advises the tower of the revised flight path.

WAGSTAFF (radio): Madang Tower, PNG 1600.

Passing 13,000 on descent, estimated Madang at one six.

CONTROLLER (radio): PNG 1600, Madang Tower. Say again your level?

Passing, uh, 12,300.

CONTROLLER: Roger, runway zero-7. Rain showers overhead passing from the east.

NARRATOR: While Captain Spencer makes a sharp descent through the clouds…

(alarm beeping)

…the plane picks up too much airspeed.

DI GIULIO: Aerodynamically, flying overspeed by a couple of knots

is not really a big deal.

Think of it like driving a couple miles per hour over the speed limit in your car.

(beeping continues) WAGSTAFF: Airspeed, mate.

Got it.

DI GIULIO: There are several ways to slow down the airplane.

You can increase the pitch of the airplane,

and this will reduce the airspeed as the airplane aerodynamically slows down.

Additionally, you can reduce the power to the engines.

(high-pitched screeching)

- (yells) What have we done? - (yells) I don't know, mate. I don't know.

NARRATOR: An ear-splitting sound makes it almost impossible

for the pilots to communicate.

DI GIULIO: It would be overwhelming.

There's loud noises that you're not familiar with.

There's smoke. There's warnings being generated by the airplane.

And it's all happening at once.

It's overspeeds. Overspeeds. It looks like double propeller overspeeds.

NARRATOR: First Officer Wagstaff notices the propellers are rotating too fast.

The plane is in a precarious state.

DI GIULIO: There could be control difficulties.

There could be engine damage.

And in severe cases, there could be engine failure.

(high-pitched screeching continues)

(yells) What have we done?

(yells) It's overspeeding. Number two is shut down.

(yells) I can't hear you!

DI GIULIO: The crew would have a very difficult time

cutting through the noise and trying to identify

the initial root cause of these problems.

(noise disappears)

NARRATOR: Finally, the deafening sound dissipates.

- You got the left side working? - No.

Okay. We got nothing.

NARRATOR: Both engines have failed. The plane is descending fast.

DI GIULIO: This crew was faced with a scenario

where they lose both the primary and the backup system

on both engines at the same time.

That backs the crew into a very difficult situation

where there is only really one outcome. A forced landing.

NARRATOR: A forced landing means the pilots have no choice

but to land immediately.

Sixteen miles from Madang Airport,

Captain Spencer turns the plane back towards the coastline.

He needs to find a safe place to put the plane down.

Tell the tower.

Madang Tower. Mayday, mayday, mayday.

(radio) Airlines PNG Flight 1600, double engine failure

and we're making an emergency landing.

Confirm you are able to make it to the field?

DI GIULIO: The optimum scenario in a forced landing

would be gliding to an airport.

Failing that, the next best choice would be landing close to a town or city.

This may increase the odds that the airport fire/rescue services

can attend to both the aircraft and its passengers and crew.

NARRATOR: But no such options exist.

Brief him that we're gonna ditch.

Negative, negative, negative. We'll probably be ditching.

DI GIULIO: A ditching is a forced landing that has to be made in open water.

It is the last choice for pilots if an alternative exists.

NARRATOR: Flight 1600 is rapidly losing altitude, and time is running out.

Look there, a river.

DI GIULIO: From altitude, a riverbed may look like a long safe area

to land the airplane in a forced landing situation.

I'll get as close to the mouth of that river as I can.

Airlines PNG 1600, we'll be ditching on a river.

Confirm location.

NARRATOR: Controllers need a location so they can send help.

Not sure the name of the river.

NARRATOR: The lives of the 32 people on board are at risk.

DI GIULIO: Pilots will remain focused right until the very end.

A pilot will not stop fighting to save their airplane.

- Do you want me to shut both engines down? - Yes! Shut everything down!

DI GIULIO: Shutting down the engines prior to a forced landing off field

could help slow the spread of any post-crash fire that may develop.

NARRATOR: Flight 1600 is now a glider.

(suspenseful music)

The Dash 8 is only a few hundred feet above the ground.

DI GIULIO: At a certain point close to the ground,

the pilots have to rely on the decision they've made

and hope that it was the right one.

Brace. Brace!

NARRATOR: Seconds from touching down, Captain Spencer sees a deadly hazard.

Boulders!

DI GIULIO: All you would have is your eyeballs.

What you see from ten thousand feet, and five thousand feet, and five hundred feet,

may look different as your depth perception increases

as you're getting closer to the ground.

NARRATOR: Two hundred feet from the ground,

Captain Spencer tries to avoid huge boulders on the riverbed.

Brace. Brace!

NARRATOR: The only option is the riverbank.

(thudding)

(metallic screeching)

(people chattering)

NARRATOR: Airlines PNG Flight 1600 has crashed into bush

near the mouth of the Guabe River.

Twenty-eight people are dead.

Just one passenger and the three-member flight crew survive.

It was a dry riverbed. So the aircraft broke up into many parts.

And then there was a post-impact fire which destroyed a lot of the evidence.

NARRATOR: The Papua New Guinea Accident Investigation Commission

rushes a team to the scene…

…and calls in help from other countries.

I was pretty keen to get the lay of the land

and see what this accident site looked like, and also get boots on the ground.

NARRATOR: Eric Blankenstein from the Australian Transport Safety Bureau

is among the first investigators at the scene.

BLANKENSTEIN: My first impressions were that this was an incredibly large

and difficult site to work,

and that we needed to prepare logistically to get this job done.

NARRATOR: The length and shape of the wreckage field

indicate how the plane came down.

Three hundred meters long.

It spreads out from the point of impact.

BLANKENSTEIN: If you have this long distance

and it has this V forming wreckage trail,

it means to us that it's a low angle of entry and also high speed.

So straight away, we would be able to get the impression

that this off-field landing was a particularly fast off-field landing.

BLANKENSTEIN: Let's see how they configured the plane.

BLANKENSTEIN: Normally, when you're doing a landing,

including an off-field landing, you would have the flaps down

so you can effectively land the aircraft slower.

The landing gear configuration, also,

you would expect them to be in the down position to soften that blow of impact.

Landing gear is up.

NARRATOR: Blankenstein finds the landing gear actuator in the raised position.

The flaps are up too.

They weren't configured for landing.

NARRATOR: Without the flaps and landing gear deployed,

the plane would have hit the ground at high speed.

But what triggered the crisis is a mystery.

This is the left engine.

BLANKENSTEIN: The left engine had separated from its wing

and broken into two sections.

NARRATOR: Did the turboprop engines play a role?

BLANKENSTEIN: Immediately, my attention was drawn

to some issues to do with the engines,

although we don't try and narrow down our focus too quickly.

Not a lot of rotational damage to the props.

NARRATOR: They can tell from the condition of the propellers

that very little power was coming from the engines.

- Were the left props feathered? - I'll check.

NARRATOR: If an engine fails,

the pilots need to adjust the pitch of the propellers so they don't create drag.

It's called feathering.

BLANKENSTEIN: Pilots generally don't feather propellers of aircraft

unless there's an engine problem.

If you feather a propeller, you no longer have propulsion to your aircraft.

The left props were feathered.

BLANKENSTEIN: Did you check the right props?

Yes, they're feathered too.

BLANKENSTEIN: When we identified

that the propellers were both in the feathered position,

immediately we were of the understanding

that there was an issue with the engines themselves.

BLANKENSTEIN: We're gonna need these airlifted out of here.

INVESTIGATOR 2: I'll arrange it.

BLANKENSTEIN: We were able to airlift those out with a helicopter to Madang

and then transport the engine sections to Port Moresby

where we could do a full and thorough examination of those engines themselves.

I've got the data.

NARRATOR: David McNair from the Transportation Safety Board of Canada

joins the investigation.

We had a notification from Papua New Guinea that the Dash 8 had crashed.

Of course, since the aircraft is manufactured in Canada,

that requires our involvement.

MCNAIR: Can we hook this up please?

NARRATOR: They focus first on the flight data recorder.

MCNAIR: The information about the engines on site was limited.

The real evidence you're looking for is the flight data recorder.

A lot of these parameters would tell you

when the engines did what and how it happened.

MCNAIR: Check this out.

NARRATOR: Investigators learn that 28 minutes into the flight,

the rotations per minute, or RPMs, spiked to 1,500 on both engines.

It's the highest level the FDR can record.

Well, that's not normal.

FISHER: So the normal operation of the propeller in the air

is about 900 RPM to 1200.

During the flight, they went above 1500.

Double propeller overspeed.

NARRATOR: Investigators discover evidence of a frightening engine condition

called a double propeller overspeed.

Overspeeding propellers can destabilize the turbines and cause catastrophic damage

if pilots don't catch the problem soon enough.

FISHER: You want the engine driving the propeller.

You never want the propeller driving the engine.

And that condition is where you see this overspeed.

Both engines saw a propeller overspeed condition, which is extremely rare.

NARRATOR: Could the double propeller overspeed

have caused the crash of Flight 1600?

MCNAIR: If the engine overspeeds fast enough and hard enough,

the parts will break, and then you don't have control of that engine anymore.

We need a closer look inside those engines.

BLANKENSTEIN: Wow. Look at this.

NARRATOR: Damage to the turbine blades in Airlines PNG Flight 1600's left engine

- provides unmistakable evidence. - It's corn-cobbed.

BLANKENSTEIN: Right.

NARRATOR: Corn-cobbing occurs when the speed of the propeller

is so fierce that it causes all the blades in the turbines to shear off.

The blades physically looked like they'd been chewed out of the power turbine.

So it gives a corncob look. And that's a feature by design,

that about 145 or 150 percent overspeed, they shed.

NARRATOR: Corn-cobbing is a protective measure that prevents the turbine blades

from spinning quickly enough to tear the engine apart.

Have a look at the right.

BLANKENSTEIN: Well, the right looks perfectly okay.

NARRATOR: Unlike the left engine,

the right turbine shows no obvious signs of overspeed damage.

The left engine had shed its turbine blades whereas the right had not.

Something completely different happened to the right engine.

BLANKENSTEIN: The right engine was feathered,

but mechanically, looking at the turbine itself, it appeared to be undamaged.

FISHER: We had assumed that both engines had been damaged during the overspeed,

but clearly the right engine didn't see as much distress as the left.

It certainly raised questions going forward with the investigation.

I can't figure it out.

Regardless, wouldn't the protective systems have kicked in?

Good point.

NARRATOR: There are three protections designed to prevent each engine

from overspeeding:

a propeller control unit, an overspeed control unit, and a backup system.

BLANKENSTEIN: Both of these propellers going above the maximum so rapidly

would have to bypass those three systems.

NARRATOR: Did the engine protection systems fail?

As in most investigations,

you start looking at what were the reasons why this was possible?

Was there a system out there that would prevent this from happening?

The answer is yes. There was a system. There was a design.

BLANKENSTEIN: Test results.

NARRATOR: Investigators analyze tests performed

on the protection systems for Flight 1600.

No data on the right engine.

NARRATOR: Inspections performed on the right engine protection systems

are inconclusive due to post-crash fire damage.

Investigators send them to the manufacturer for deeper analysis.

Maybe they can figure out what happened to it.

What about the left?

NARRATOR: The left engine isn't as badly burned,

and inspections provide a critical answer.

All three protections were operational.

NARRATOR: If the protection systems on the left engine were working,

why didn't they prevent an overspeed and eventual corn-cobbing?

(engine droning)

Bypassing three systems of protection at the same time

would be a statistical improbability.

So we knew that there was something else involved in these propeller overspeeds.

Let's see what the pilots have to say about what happened.

NARRATOR: The team reviews transcripts of interviews with the two pilots.

BLANKENSTEIN: You obviously build a list of questions you want answers to.

What was in your mind's eye at that point in time?

Were you aware of why the propellers oversped?

You know, what were your actions at the time?

The captain said there was a lot of cloud cover on approach.

What else?

- I'm gonna take us down. - Copy.

(engine rumbling)

BLANKENSTEIN: But out of the blue, the airspeed warnings started to sound.

(alarm beeping)

NARRATOR: As Captain Spencer started his descent below the cloud,

a warning sounded alerting him that the plane was going too fast.

(beeping continues)

What did he do?

He said he raised the nose.

Pulled back on the power.

Sounds right.

Agreed.

WAGSTAFF: Airspeed, mate.

Got it.

DI GIULIO: If you get a speed warning, you need to slow down.

The first and most obvious is being to reduce the power.

Think of it like taking your foot off the gas pedal in your car.

NARRATOR: The Captain's testimony doesn't provide any new leads for investigators.

What did the first officer have to say about the airspeed warning?

Get this. He says once the warning sounded,

the Captain yanked the power levers back quickly.

NARRATOR: First Officer Wagstaff's testimony adds a crucial detail.

MCNAIR: And the co-pilot particularly indicated that

the power levers were brought back very quickly,

then the problem happened right after that.

(high-pitched screeching)

SPENCER (yells): What have we done?

His instinct to pull the power levers back was correct.

But did something happen when he pulled them back quickly?

Maybe he pulled them back so fast they went all the way into ground beta mode.

NARRATOR: The power levers on the Dash 8 have two settings:

flight mode and ground beta mode, used only when the plane is on the ground.

BLANKENSTEIN: You need a mode where you can taxi the aircraft

and have direct pitch and power control over the propellers themselves.

It allows you to operate the aircraft more simply on the ground.

NARRATOR: Pilots are trained not to put the plane into ground mode while airborne.

FISHER: The only time to be in the ground range is when you're on the ground,

when you are starting the aircraft, when you're maneuvering the aircraft,

when you're taxiing the aircraft.

If you put the plane in ground mode mid-flight,

would that disarm those overspeed protections?

Let's look at the flight manual.

Listen to this.

If pilots put the plane into ground mode mid-flight,

it would have disabled the protection systems.

(alarm beeping)

(high-pitched screeching)

FISHER: If he's pulled the power levers back rapidly,

you're now into no man's land.

You're on the precipice of disaster because you have no propeller control.

So this is a case of pilot error then.

Maybe.

But maybe not.

Don't the power levers have a protective gate between flight mode and ground mode?

That's correct.

NARRATOR: A mechanical stop, or gate,

prevents pilots from moving the power levers into ground mode by mistake.

Triggers on the power lever lift the gate, allowing movement to ground mode.

You have to physically move your hand around

the front of the power levers to reach those two small tabs,

and you pull them vertically up and then you can move it back.

But it's certainly nothing you would want to do in the air.

NARRATOR: Investigators need to find out if the mechanical gate

was working properly on Flight 1600.

It looks like some of the pieces survived the crash.

The trigger springs are burned from the post-crash fire, but they're still good.

NARRATOR: Did the power lever triggers fail,

(alarm beeping) allowing the propellers to overspeed?

(high-pitched screeching)

The wreckage information was limited.

Quite a bit of stuff was destroyed by the fire.

But the things that were there were analyzed.

In this case, one of them was the trigger spring.

NARRATOR: The spring is supposed to hold the power lever triggers in place.

BLANKENSTEIN: They've still got resistance.

FISHER: The spring was working correctly and the triggers were working as designed,

and so we could see that in the inspection.

If the triggers were working, how easy would it be for the captain to lift them

and pull the lever into ground mode?

BLANKENSTEIN: We decided to look at the human factors aspects

of the protection system, trying to ascertain

how much you needed to lift the triggers to take it below the flight idle gate.

So I ran a test on the levers.

First, I tested the levers to see how well the gate works.

I didn't touch the triggers.

- The levers came to a full stop. - The gate worked as designed.

Correct. So then I did it again, this time quickly.

NARRATOR: Blankenstein simulates the captain's physical reaction

to the airspeed warning.

Without even trying, I pulled the triggers.

INVESTIGATOR 2: That shouldn't happen.

NARRATOR: The team discovers how easily the pilots

could have put the plane into ground mode by mistake.

BLANKENSTEIN: We noted during testing of the power levers

that if you were moving the power levers back quite rapidly,

we could see how it would be quite simple

to actually inadvertently pull the triggers

without even realizing that you'd done it.

NARRATOR: The pilots only needed to lift the triggers six millimeters

for the levers to move past flight idle and into ground mode.

DI GIULIO: I don't think anybody who flew the airplane at the time

was aware that a six millimeter pull of one trigger

could cause both engines to go into propeller overspeed condition.

NARRATOR: But did Captain Spencer actually do what investigators suspect?

We're four minutes before they crash. Let's start.

NARRATOR: Investigators listen to the cockpit voice recorder

to confirm their theory that the captain pulled the power levers into ground mode.

SPENCER (recording): I'm gonna take us down.

WAGSTAFF (recording): Copy.

NARRATOR: They hear the Captain begin an early descent to avoid bad weather.

MCNAIR: The cockpit voice recorder records the voices of the people in the cockpit

but it also captures all the noises,

and the noises can be very useful for analysis.

NARRATOR: Soon after, the airspeed warning sounds.

It fits with what the captain told investigators.

(alarm beeping)

- WAGSTAFF: Airspeed, mate. - SPENCER: Got it.

(high-pitched screeching) Whoa. That is a wall of sound.

It's the sound of the propeller overspeed.

(high-pitched screeching)

FISHER: It's very, very loud

'cause the propeller tips are breaking the speed of sound

and so you get these really, really high sonic booms

back and forth, a lot of vibration, a lot of noise.

MCNAIR: Go back five seconds.

I thought I heard something before the propeller overspeed.

NARRATOR: As they listen to the cockpit conversation…

- WAGSTAFF: Airspeed, mate. - SPENCER: Got it.

NARRATOR: …a tiny sound catches the team's attention.

(click) Did you hear that?

I heard something. It's hard to tell what exactly.

Can you delete the sound of the props?

NARRATOR: Investigators sift through the layers of sound in the cockpit.

Try losing the sound of the alarm as well.

(alarm beeping)

(alarm stops)

MCNAIR: Okay. Amplify what's left and let's have a listen.

(click)

BLANKENSTEIN: There it is.

NARRATOR: Buried deep within the noise of the cockpit,

they discover what they're looking for.

BLANKENSTEIN: This clicking sound just before the propeller overspeed

was perhaps the pilot in command

pulling the triggers upwards into the ground beta range.

MCNAIR: Now we're getting somewhere.

NARRATOR: Right after the click, they hear another critical sound.

(muffled squeak)

It's the beta warning horn, initially drowned out by the overspeed noise.

BLANKENSTEIN: The beta warning horn sounds when you take the power levers

into the ground beta range.

(muffled squeak)

It was intermittent, and it was very difficult to hear

above the sound of the propellers themselves.

So we could hear these little tweeting sounds

on the cockpit voice recorder that indicate that that was the case.

(engine droning)

(alarm beeping)

- WAGSTAFF: Airspeed, mate. - Got it.

NARRATOR: It's definitive proof that confirms the investigators' suspicions.

The captain put the plane into ground mode mid-flight…

(Pilots gasp)

NARRATOR: …causing the propellers to overspeed.

FISHER: The flight manual states specifically

never to go below the flight idle gate. It's prohibited as a matter of fact.

But if it's so easy to do, how come it hasn't happened before?

That's a good question.

NARRATOR: Was the crash of Flight 1600 caused by an unlikely pilot error,

or was there a deficiency with the Dash 8 that allowed it?

FISHER: We need to find out whether we have a problem with the fleet.

We wanted to make sure that the thousand aircraft

that were out there were operating safely.

(engines drone)

INVESTIGATOR 2: This can't be the only case.

NARRATOR: Investigators look for evidence of other pilots

who have made the same mistake as the crew of Flight 1600.

(phone ringing)

Yes?

Really?

BLANKENSTEIN: About two months after the Madang accident,

there was an incident involving a Dash 8 where the propellers had oversped.

BLANKENSTEIN: Right. Thanks.

- It's happened again. - What's happened?

BLANKENSTEIN: An incident just like Flight 1600. Just a few days ago.

NARRATOR: The team learns about another crew in Australia

that put a Dash 8 into ground mode mid-flight.

BLANKENSTEIN: In that particular case,

the first officer had their hand on the power levers

and they experienced an updraft followed by a downdraft

and inadvertently gripped the triggers of the power levers

and moved the power levers below the flight idle gate.

The pilots got out of it. They put it back into flight idle right away.

Everyone's fine.

Those aren't the only incidents. There are more.

NARRATOR: The most recent incident is just the tip of the iceberg.

Investigators uncover six other cases

where Dash 8 pilots mismanaged the controls of the Pratt and Whitney engines

by pulling the power levers into the ground mode mid-flight.

BLANKENSTEIN: It was pretty obvious to us

that inadvertent activation of the power levers into the ground beta range

can occur and will occur in the future.

INVESTIGATOR 2: The NTSB has been on top of this for years.

They wanted stops on the power levers

to prevent moving into ground mode during flight.

- BLANKENSTEIN: What about the FAA? - I asked myself the same question.

They followed suit. It was mandated.

A lockout system was built for the Dash 8 so this wouldn't happen again.

They fixed the problem.

MCNAIR: The design of the system was reviewed,

and there had been many changes as to try and make this gate less easy to cross.

They knew about this ten years ago.

So why didn't Flight 1600 have this system?

Have a look.

- This is only in the US. - INVESTIGATOR 2: Exactly.

BLANKENSTEIN: The Dash 8s in the United States

had to incorporate a system that prevented propeller overspeed

when you went into the ground beta range.

And the rest of the world didn't incorporate that system.

If they had mandated this here, it could have saved lives.

NARRATOR: Investigators conclude that the power levers

of hundreds of Dash 8s around the world have a dangerous flaw.

(engine droning)

But there is one remaining issue to resolve.

Did we get the results from the manufacturer

of what happened to the right engine?

NARRATOR: Even though both engines experienced the same overspeed forces,

why wasn't the right engine destroyed in the same way the left one was?

BLANKENSTEIN: It looks like the switch that activates the propellers

was improperly maintained.

NARRATOR: Shortly after the right propeller oversped,

it got stuck in the feathered position and was unable to produce any thrust.

So it's effectively in neutral.

It's not in drive. It's not in reverse. It's just going with the airflow.

NARRATOR: This prevented the right engine from corn-cobbing like the left one.

It's the final piece of the puzzle.

So Captain Spencer puts the plane in a fast descent.

NARRATOR: Investigators finally understand the sequence of events

that caused Flight 1600 to crash.

- I'm gonna take us down. - Copy.

NARRATOR: As it heads for Madang, thick clouds are in the plane's path.

The Captain wants to see the airport.

Understandable. But he starts going too fast.

(alarm beeping)

BLANKENSTEIN: Now, around here, at 10,500 feet, the airspeed warnings go off.

(alarm beeping) WAGSTAFF: Airspeed, mate.

Got it.

BLANKENSTEIN: He pulls the power levers back,

accidentally putting the plane in ground mode.

(high-pitched screeching)

(airplane drones)

(yells) What have we done?

BLANKENSTEIN: Both engines malfunction for different reasons,

and the plane is now a glider.

It was the worst of cases, the worst of consequences

when you lost both engines, and then you have to do this off-field landing.

INVESTIGATOR 2: How long did it take for them to hit the ground?

BLANKENSTEIN: The propellers oversped here. So… four minutes, 18 seconds.

That's not a lot of time for an emergency landing.

Madang tower. Mayday, mayday, mayday.

NARRATOR: But was that enough time to find a safe landing spot?

MCNAIR: We needed to know: How did the crew manage the flight?

What could they have done? What did they do?

Investigators examine how the pilots of Airlines PNG Flight 1600 reacted

after both their engines failed.

What were they doing?

- (yells) What have we done? - (yells) I don't know, mate. I don't know.

Or what were they not doing?

NARRATOR: They turn to the transcripts from the cockpit conversation

to see if the pilots performed checklists from their quick reference handbook

in the final four minutes of flight.

MCNAIR: When you have both engines out, you're faced with a forced landing.

And there is a checklist for forced landing.

Mayday, mayday, mayday. Airlines PNG Flight 1600.

We're making an emergency landing.

MCNAIR: And the typical forced landing checklist

has some basic guidance in terms of what speed they should fly.

NARRATOR: Reducing speed gives pilots more time to locate a suitable site

and prepare for an emergency landing.

The forced landing checklist would tell them to lower the flaps

and put the gear down once they've chosen a site.

NARRATOR: But there's no discussion about the checklist.

They weren't running any checklists at all.

DI GIULIO: Instead of establishing the airplane in a best glide configuration,

they increased their descent rate and sacrificed a lot of the altitude

that could have been advantageous for them in selecting a forced landing site.

Look there. A river.

MCNAIR: The crew reacted, but they didn't seem to do any sort of problem solving

in terms of what was the best option.

For example, they didn't even discuss what speed to fly.

If they configured their plane for a glide,

what speed would they have been flying?

Hold on.

NARRATOR: The investigators determine the speed the pilots could have slowed to

in order to maximize their glide time.

1.3 times stall speed…

2.5 miles per 1000 feet.

That's 120 knots.

NARRATOR: When they compare the glide speed to that actual speed of the flight,

investigators come to an eye-opening realization.

They were going up to 250 knots after the propellers oversped.

INVESTIGATOR 2: Twice as fast as they should have been.

NARRATOR: How much longer could the pilots have stayed airborne

if they had maintained the recommended glide speed?

They could have bought themselves six more minutes of glide time.

DI GIULIO: That additional time could have come in very handy for several reasons.

It would have conserved the energy of the airplane and allowed them to fly longer.

It also would have given them more time

to perform the appropriate drills and checklists

that would have helped them have a more successful outcome

from the forced landing.

I'll get as close to the mouth of that river as I can.

NARRATOR: Instead of slowing the plane and assessing all his options,

the captain tries to get on the ground as quickly as possible.

Following the overspeed, the rate of descent of the airplane increased

from 1,500 feet per minute to 6,000 feet per minute.

That's a staggering descent rate.

The last thing that you would want to do after having lost both your engines

is trade away all of your altitude.

NARRATOR: With less time to plan for a ditching,

the pilots choose a difficult landing site.

DI GIULIO: Airplanes are designed to take

the structural load of landing on a firm surface

using the systems that we have on board, like landing gear and flaps.

The systems aren't designed in a conventional airplane to land on water.

Boulders!

NARRATOR: In the end, boulders prevented any chance of ditching on water.

Forced to land on the riverbank,

PNG Flight 1600 wasn't properly configured for landing on the ground.

(suspenseful music)

(thudding)

(metallic screeching)

MCNAIR: So many people died on this accident.

This was an eye-opener and made everybody realize in fact something had to be done

to prevent this kind of situation.

Good job.

NARRATOR: The investigation into the crash of Airlines PNG Flight 1600 concludes

with a clear recommendation.

You can't just say pilot error and be done with it.

You have to say, why was the error possible?

Why wasn't the error eliminated? In this case, it's the design of the airplane.

NARRATOR: A change that has long been made in the United States

was not mandated in the rest of the world.

BLANKENSTEIN: We had enough evidence to be able to force change.

We used the power of the pen and the facts

and the evidence that we had identifying safety issues,

and we presented that to the manufacturer and Transport Canada, and they did change.

NARRATOR: A ground beta lockout system is now mandatory

in every Dash 8 aircraft worldwide.

FISHER: It was always a good airplane.

But now we've had to make the system so that a purposeful act or unintentional act

is now safer. I mean, you can't do it anymore if you wanted to.

BLANKENSTEIN: So in this particular case,

we were able to really get down to what had occurred

and make those safety improvements.

And as an investigator, that's all you can ask for.

It's why we do the work that we do.

We just want to improve the system and ultimately save lives in the future.