Nok Air incident with tow truck

[Benzhangar 108]

An airport worker was killed this morning (Feb 7) and another was injured after a plane crushed a tow truck while it was being pulled to the gate. The Boeing 737 was being moved into position to collect passengers at the Don Mueang International Airport in Bangkok, Thailand, at around 8am local time when the accident happened. A connecting bar between the Nok Airplane and the tow truck snapped. The aircraft then continued rolling forward with the momentum before crushing the white vehicle under its body next to the wing. Engineer and groundworker Thanisorn Oncha-am was rushed to hospital but it was later confirmed that he had died from ''severe injuries sustained in the crash''. A second mechanic who was in the tow tractor was injured in the collision. CCTV footage of the incident appears to show that the towing tractor was unable to move after the bar snapped. It was then trapped under the huge plane, which has 189 passenger seats and distinctive orange and yellow bird livery. Airport director Samphan Khutharanon said: ''The Nok Air flight DD6458 from Don Mueang to Nakhon Si Thammarat collided with a Nok Air tow truck. ''The accident happened while the truck was dragging the plane to the gate to wait for passengers to travel. ''The towing device that connects the vehicle to the plane broke, causing it to stop while the plane continued moving forwards.'' Nok Air Scheduled flight DD6458 from Bangkok to Nakhon Si Thammarat in the south of the country was delayed while authorities began investigating. The regional carrier is now taking the plane out of duty in order to assess the damage and investigate what caused the crash. A new plane was used for the 8.40am flight and it departed at 9:50am. Nok Air, a publicly listed company on Thailand's SET exchange, said in a statement that they were now waiting for a post-mortem examination to confirm exactly how their employee had died. The said: ''One member of ground staff in the tow truck was seriously injured and died at the hospital and another injured officer has been taken to the hospital.

 

 

Another source:
http://newsinflight.com/2020/02/07/tug-driver-died-when-nok-air-boeing-737-rolled-over-the-tug/

Edited February 8, 2020 by Benzhangar

[Chock 17,769]

This is why there is a very specific procedure which you adhere to when towing: In the tug passenger seat, you have a second person on a headset connected to the cockpit who monitors the towbar all the time to see if the shear pins have broken, if that person sees them break, they immediately give the call 'x-ray, x-ray, x-ray' which means two things: The guy on the brakes in the cockpit immediately applies the maximum braking effort he can and the tug driver immediately 'floors it' to get out of the way.

Since there can be passengers on board when towing, this is one of the reasons why you don't tow at a high speed, because if you have to slam on the brakes in the cockpit, you could injure a passenger. But beyond this reason, the tug should never tow at high speed because it puts a strain on the shear pins, making it more likely that a pin will break, especially in a turn, and the tug should always have plenty of speed capability in reserve for exactly this kind of incident, which it will not have if it is towing at high speed.

It's sad that the accident occurred, but frankly, I suspect that these guys were not doing any of that stuff, which makes it an accident waiting to happen.

Edited February 8, 2020 by Chock

[mwilk 1,110]

That was the first thing I thought of. It sure seemed like he was towing at a high rate of speed. I've towed and I've ridden the brakes. If something goes wrong you have just a split second to react before very bad things happen.

 

[Chock 17,769]

Yeah, I do see people towing at quite high speeds on occasion (and stay well clear of them) and I sometimes see tug drivers towing alone (some service companies allow that, others not) but I always think it's not a good thing to be doing that sort of stuff.

Back when we were still servicing Thomas Cook airliners, we had a couple of guys who had the towbar shear pins break on a pushback, and the turning forces at the time of the break were so strong, they actually swung the towbar and the tug sideways! In fact, the force swung the tug so much that the headset guy had to run out of the way of it. Unfortunately, he decided to run forward a bit too, putting him right near the operating starboard engine. Fortunately he didn't get close enough to get ingested, but he got pretty close then realised the danger. He was so shaken up that they sent him home that day, which was probably a good decision.

It's easy to forget about dangers, such as just how much airliners and GSE weighs and how much momentum things will have, and then get complacent about it. For example, we had a big Schopf tug go tech the other day on a pushback; it wouldn't engage its gears. It was swapped for another tug, but of course someone had to push the broken tug into an equipment bay. To do that they used a good old Charlatte T135 EBT. We were on the next stand waiting to push out a BA A321, and someone said they were surprised that an EBT could actually push the tug, but I pointed out to them that even though those little EBTs look dinky and cute, they have a tractive force of 15,000 Newtons and are rated to pull over 4,000 lbs.

Personally, I take note of things such as the placards on GSE and airliners when I'm doing walkarounds and stuff, such as where it says the system has a hydraulic pressure of 3,000 PSI, or the tire pressure is placarded as 214 PSI. It's a sobering reminder of the kind of forces which could be involved if something goes awry. 

Edited February 8, 2020 by Chock

[HighBypass 2,339]

Is there a possibility that NO ONE was in the cockpit? The plane only seemed to come to a stop when the tug got jammed? IS there any airport in the world where it is acceptable to tow airliners without anyone covering the airliner's brakes?

Fluid at 3000 psi exiting a fractured hose will quite easily act like a syringe from hell and inject itself right into the body parts of anyone unfortunate enough to be in the way... if it's on a hard working vehicle such as an excavator or forklift busy all day then the hydraulic fluid might be hot enough to scald you as if being injected wasn't bad enough already! 

 

[FDEdev 955]

4 minutes ago, HighBypass said:

Is there a possibility that NO ONE was in the cockpit? The plane only seemed to come to a stop when the tug got jammed? 

No. The heavily compressing nose gear is a good indicator for a pretty strong brake application.

[HighBypass 2,339]

A fair point, thanks. I  initially thought that jamming something close to the main undercarriage caused that heavy nose compression.

[Chock 17,769]

37 minutes ago, HighBypass said:

Is there a possibility that NO ONE was in the cockpit?

Generally speaking that would never happen. Tows are pretty strictly regulated, they even have one of those little wooden sequence markers for them up in the control tower (or these days more likely the electronic equivalent) which all the departing aircraft have. That's because a tow is of course still an aircraft movement as far as ATC is concerned. As such, you have to phone up the tower and let them know it is planned and you have to call for permission to do one on the ground ATC frequency, whereby they will give you a route to follow just like they do with aircraft which are taxying. You also have to report in when you're on stand having finished the tow.

Unlike on most aircraft, where ATC send the crew a text version of their taxi route, making it sound to anyone listening as though nthe crew have got a brilliant memory when they read back perfectly the complex taxiway route they've just had rattled off to them at high speed from ATC when in fact they're actually reading it off a screen. In a tug you haven't got that helpful facility, so again that's another thing the headset guy in the tug can do, i.e. write down the taxiway route in the condensation on the windows (or at least that's what I always do lol).

Beyond the requirement for someone to 'ride' the brakes for safety reasons, you'd need someone to be in the cockpit to release the parking brakes before you pushed the thing of stand onto the taxiways in order to begin towing it to its new stand, and you need someone to turn on the anti collision beacons too, which have to be on for towing, unless they are inoperable, in which case the airport will usually put a follow me car in front of and behind the aircraft on tow with their lights flashing.

This is another reason why it is a good idea to have two people in the tug, because when the tug comes to a halt having completed the tow, the driver will be calling the tower to let them know he's off the taxiways and also holding the tug still on the brakes, so whilst all that is happening, the headset person in the tug can jump out and give the brakes on signal to the person in the cockpit and get some chocks in, disconnect the tow bar etc, or use the headset to ask for brakes on, although personally I've always used hand signals and waited get a hand signal 'brakes on' response from the cockpit, as there is no mistaking that.

The need for someone in the cockpit on a tow is actually one of the annoying things about doing tows; sometimes you've got everything connected up and you're ready to start, but you end up sat there in a tug waiting ages for an engineer to turn up so he/she can sit in the cockpit and perform those duties.

Edited February 8, 2020 by Chock