On the sixth of February 2023, a Boeing 737-3H4 Massive Air Tanker crashed right into a ridge line of 222 toes elevation in Fitzgerald River Nationwide Park in Western Australia.
There have been two pilots on board. The captain was very skilled with multi-engine air tankers and held his United States Forest Service (USFS) Air Tanker Coaching Pilot qualification. He had 8,233 hours flying expertise, together with 1,399 hours on the Boeing 737 and 5,500 hours aerial firefighting expertise. He spent a number of years on the US Nationwide Aerial Firefighting Academy instructing different aircrews earlier than becoming a member of the operator and had develop into the director of operations there in 2017. The primary officer had 5,852 hours of flying expertise with 500 hours aerial firefighting expertise. Nonetheless, he didn’t have as a lot expertise with giant air tankers, with simply 128 hours on the Boeing 737.
The Boeing 737 was 28 years previous and registered within the US as N619SW. It had 69,016 hours when the operator bought it in 2017.The Boeing was modified for its new goal a an aerial firefighter tanker with the set up of a Retardant Aerial Supply System. Two tanks had been put in to carry hearth retardant, with a complete capability of 36,000 kilos (~16,300 kilos). The transformed Boeing 737 bomber was given the decision signal Bomber 139.
Within the cockpit was a person interface with a change on both aspect. If both crew member activated their change, the door would open to drop a predefined degree of fireplace retardant, based mostly on the tank ranges, floor pace and plane top above the bottom. There was additionally an emergency dump change to dump the complete load in underneath two seconds.
Each instrument panels had radio altimeter indicators which displayed the peak above the bottom when flying under 2,500 toes above floor degree. It was potential to set a call top (DH) on these altimeters, which activated a light-weight marked as DH. For example, you’ll be able to see within the picture above that the choice top is about to 50 toes above the bottom.
On the sixth of February, hearth controllers noticed a harmful hearth west of Hopetoun, Western Australia. The fireplace was burning by an space with excessive gasoline hundreds, that means it might unfold rapidly. They referred to as in aerial assist to assist include it.
The State Operations Air Desk coordinated the aerial response. They despatched out a number of requests for plane all through the day.
Bomber 139 was a kind of who responded. The plane and crew made two profitable flights from Busselton airport, dropping retardant on the hearth and returning to base. The accident flight was their third flight of the day. The flight crew described their psychological fatigue degree as advantageous however not at peak.
Three plane labored collectively on the web site:
A smaller plane, known as Birddog, gathering intelligence to find out the perfect flight path, guiding the bomber to the correct spot and utilizing a smoke generator to inform them the place to drop
Bomber 139, the big air tanker who would carry and drop hearth retardant following the Birddog’s steering
An Air Assault plane circling excessive above to coordinate all the operation.
At 15:19, the unique Birddog who had been offering the reconnaissance assist for the earlier drops (callsign 125), wanted to refuel. Earlier than leaving, the crew took their alternative, Birddog 123, on a familiarisation flight across the hearth zone. They defined the structure of the hearth and the plan for the retardant drops however didn’t point out any hazards within the space.
Ten minutes later, Bomber 139 departed Busselton with a recorded gross weight of 124,640 kilos, of which the hearth retardant payload was 35,200 kilos. At quarter-hour out, the captain contacted Birddog 123. Birddog 123 responded with the present QNH setting (barometric strain). The captain of Bomber 139 acknowledged the altimeter setting and stated they’d contact the first air assault plane after they had been 5 minutes from the hearth.
The Air Assault plane cleared Bomber 139 into the zone with a ceiling of two,500 toes. Birddog 123 confirmed the world was clear; no floor personnel had been anticipated for an additional hour.
The captain of Bomber 139 was the Pilot Flying and the primary officer was Pilot Monitoring. The primary officer briefed the captain on their goal drop pace (VDROP) of 133 knots.
The captain reported that that they had visible contact with Birddog 123.
Birddog 123’s pilot provided them two choices:
A “Present-Me” run: a cross over the goal to reveal the road and begin level of the retardant drop, giving the Bomber 139 crew a preview of the terrain
A low-level drop sample (underneath 500 toes) following Birddog 123
The captain selected the second choice, to comply with Birddog 123 straight for the drop.
Birddog 123 briefed them on the goal space: they’d use a highway as the beginning level to increase the prevailing line of retardant. They agreed to make use of right-hand circuits, maintaining the smoke to the left.
Bomber 139’s captain reported that they had been in place after which requested the primary officer to finish the pre-drop guidelines.
The operator’s procedures required calculating a goal drop pace (VDROP) based mostly on the plane’s configuration particularly, 1.25 instances the minimal regular flight pace. After every partial drop, this goal pace was recalculated and lowered to account for the lowered weight of the remaining load.
The captain contacted Birddog 123 to say that their goal pace can be 135 knots for last with flaps set to full (flap-40).
Birddog 123 briefed them on the drop: they anticipated a a straight exit with no hazards, however it will be a downhill strategy. The goal altitude was 500 toes descending to 400 toes.
A downhill strategy, or flying downhill, is when a low-level plane is following falling terrain, which implies that the plane should proceed to descend with the intention to preserve the identical top above the bottom. A downhill strategy is often flown at idle engine energy, because the plane will slowly acquire pace within the descent.
After Bomber 139’s first officer confirmed that the guidelines was full, the captain commented that their strategy path following Birddog 123 seemed to be excessive. Birddog 123 referred to as to say they had been turning for his or her last heading of 155° and that they’d have good visibility as soon as they cleared the smoke.
Within the cockpit, the captain requested concerning the highway serving as the beginning level of the drop. The primary officer pointed to the highway, which was simply forward of them. They had been able to go.
Birddog 123 repeated the important thing factors of the briefing. “Begin on the highway and preserve all smoke to the left. 3, 2,1, begin. Your goal altitude is 500 descending to 400 toes.”
The captain confirmed that that they had the highway in sight. They descended, with their lowest top being 78 toes above the bottom. With the engines at 70% N1, they maintained 124 knots as they accomplished a nine-second partial drop, which emptied three-quarters of their retardant. The captain stopped the drop as their retardant line entered an already burnt space and reported the partial drop to Birddog 123. They would want a second cross to tag and prolong the primary drop with the remaining retardant.
“…and head down off the hill,” stated the captain on the radio, anticipating one other downhill strategy. The Birddog had briefed a ‘downhill’ drop with no hazards.
The primary officer recalculated their goal pace for the lighter load, which was now simply 118 knots. As they adopted Birddog 123 for the second cross, the captain once more questioned the strategy path. The captain requested Birddog 123 to gradual to 120 knots for the following drop. Birddog 123 acknowledged and briefed the bomber crew for the ultimate cross: “Tag and prolong all current retardant, …begin on the hill because it pushes down. Goal altitude 500 descending 400.”
The primary officer reported that flaps had been set to 40 and the pre-drop guidelines was full. The captain once more commented once more that he was sad with the strategy path that Birddog 123 was taking. One thing was clearly niggling at him however he didn’t elaborate.
Birddog 123 set them up for the drop. “That is last, absolutely retardant drop out right here in a second. Standby… Retardant is correct at our 12 o’clock… Three, two, one: tag and prolong current retardant.
They flew by the smoke drifting from the hearth; the captain later stated that they couldn’t see the goal till they cleared the smoke initially of the drop. The primary officer agreed, saying that they couldn’t even discover the goal on last till Birddog 123 deployed smoke over the placement to assist them determine it.
They descended to 57 toes above the bottom with the airspeed at 110 knots. The engines had been left at a excessive idle (30% N1) as they prolonged the retardant line downhill.
In the course of the drop, the plane recovered to 81 toes above the bottom with their pace decaying to 107 knots.
The primary officer didn’t make any call-outs about their deteriorating state, commenting later that his consideration was fastened on the airspeed indicator and the radio altimeter.
The captain began to extend the thrust as they had been rapidly descending, with a peak of 1,800 toes per minute. The primary officer’s hand moved to the flap lever, ready for the decision to retract the flaps, which would scale back the drag and permit them to climb away.
On the identical time, the captain began to pitch the nostril up. Their charge of descent slowed however so did the airspeed as they traded pace for altitude.
On the level when the thrust lever reached the setting for go-around thrust, the plane was 30 toes above the bottom and nonetheless descending at 480 toes per minute, travelling at 105 knots.
The captain referred to as “Fly airplane!” That is an pressing instruction to desert every thing else and deal with elementary plane management. The stick shaker activated. The engines spooled as much as their full energy setting.
It was too late. They hit the ridge at 104 knots.
The Boeing 737 tanker, with the engines at 85-89% N1, saved going, smashing by foliage at simply over two-hundred toes earlier than hitting the bottom a second time. Above them, Birddog 123 broadcasted MAYDAY on all stations.
Because the bomber slid to a cease, the flight crew should have been stunned to search out themselves sitting unscathed within the cockpit. The primary officer instantly began the evacuation guidelines. The cabin door had buckled and though they each tried, they couldn’t get it open. The primary officer tried and did not open the right-side window. The captain tried the identical on the left-side window. Flames appeared; the plane was on hearth. On a second try, little question pushed by adrenaline, the 2 pilots managed to get the left-side window and climb out of the cockpit.
Two single-engine air tankers had been above, dropping water with foam onto the hearth, considering the crew had been nonetheless trapped inside the Boeing. It should have appeared a miracle after they noticed the captain and the primary officer away from the wreckage with solely minor accidents. A helicopter rapidly descended and picked them up.
Bomber 139 was destroyed.
Subsequent week, we’ll take a more in-depth take a look at what occurred, and why.
