FR 737 taxis with towbar stuck under engine

[70 Mustang]

what about 737s?

Originally Posted by Australopithecus

I don’t know if modern day Boeings still require a clearance to pressurise, but 737s do.

I’ve flown most models of the 737 in 6 different airlines in 4 different countries and never once have I ever seen “cleared to pressurize”

[Australopithecus]

Well, I have flown most too, from the 200 basic on up to the -800. Ground clearance to pressurise hydraulics became a procedure in the mid 90’s and remains with us still.

[70 Mustang]

Key word is “us”

With bypass pin in, are not the hydraulics blocked from the nose gear? They did show us the pins as they left.
if that’s what you meant by being cleared to pressurize, okay. I get that.

A few times, even when seeing the pin, we still couldn’t steer the aircraft.

GENERATORS 1 …… ON
APU switch ................. As required
START SWITCHES...... CONT
PROBE HEAT switches ......... ON
WING ANTI–ICE switch................... As required
ENGINE ANTI–ICE switches ................. As required
PACK switches............................. AUTO
ISOLATION VALVE switch........... AUTO
APU BLEED air switch ..................OFF
FLAPS................... ___REQUIRED, ___SELECTED, GREEN LIGHT
Flap position indicator and FLAP lever - Set for takeoff

[Brian Pern]

Originally Posted by 70 Mustang

With bypass pin in, are not the hydraulics blocked from the nose gear? They did show us the pins as they left.
if that’s what you meant by being cleared to pressurize, okay. I get that.

FLAPS................... ___REQUIRED, ___SELECTED, GREEN LIGHT
Flap position indicator and FLAP lever - Set for takeoff
Three aspects of the Flap selection must be confirmed by the Captain in response to the Challenge “Flaps”.
“______ Required”

These look suspiciously like Ryanair SOP's. I say this, because having been around the block a few times, I have never come across it, the only time is with ex Ryanair crew.

But I digress, back to the Pressurise Question, I have always asked the ground crew 'are we clear to pressurise Hydraulics' , they go on just before push and off as part of the engine shutdown, I know this is not fashionable, certainly in the above mentioned company, but you really don't want Skydrol at 3000psi hitting you on the walk round, leaks are bad enough, worse under pressure.

But what do I know TRE, over 30 years in Jurassic's, Classic's and NG's (mainly BBJ) visiting several hundred airports in process.

Until we really know what happened, I will reserve placing blame on the crew, it is interesting there is a video though, I would have though the ground crew would be trying to get the cockpits attention somehow.

[Locked door]

The “clear to pressurise” is more about the sudden movement of parts of the aircraft than about leaks.

Before you are cleared to pressurise all flight controls will be checked clear of obstruction (fuel truck, de ice rig etc), no personnel near gear doors or under the A/C and the steering bypass pin inserted. That way if something moves suddenly on application of hydraulic pressure no one will get hurt or no damage will occur. Hopefully.

[Nightstop]

A few times, even when seeing the pin, we still couldn’t steer the aircraft.

The 737 NWS bypass pin is made of two concentric metal tubes, the outer of which has the flag attached. In an internal bypass pin failure, it is possible for the outer tube with flag to be removed but inner tube to be left behind and still engaged. The result? Impossible to use the NWS for directional control. Has happened to me.

[HOVIS]

Originally Posted by 70 Mustang

I’ve flown most models of the 737 in 6 different airlines in 4 different countries and never once have I ever seen “cleared to pressurize”

It's been standard procedure on all the Boeings I've been involved with since the early 1980s.
Main reason, to ensure we don't pressurise the steering system with a tow bar attached and no lock out pin fitted. As explained above, other reasons exist too.

[Krystal n chips]

Originally Posted by HOVIS

It's been standard procedure on all the Boeings I've been involved with since the early 1980s.
Main reason, to ensure we don't pressurise the steering system with a tow bar attached and no lock out pin fitted. As explained above, other reasons exist too.

Notably the inboard Krueger flaps on the 737 .

[DaveReidUK]

A steering input that succeeds in turning the NLG when the towbar is detached from the tug, but still attached to the aircraft, can have potentially fatal results.

[Elle Overdee]

AAIB Bulletin 01/2022 has a report on a similar incident from last June. (AAIB 27402).
Human factors/ground crew coordination.

[DCS99]

Why?

Zurich has been using towbar-less push-back tugs for 34+ years.

Why do we even have towbars in the 21st Century?

[TCTC]

I've often wondered why aircraft don't have rear-looking cameras.

[Chiefttp]

Originally Posted by DCS99

Zurich has been using towbar-less push-back tugs for 34+ years.

Why do we even have towbars in the 21st Century?

$$$$$$$$\££££££\€€€€€€

[The Bartender]

Originally Posted by DCS99

Why do we even have towbars in the 21st Century?

Because a basic tug can be adapted to any aircraft with the use of a relatively cheap towbar, and the same tug can push a 15 ton turboprop one moment and switch over to a 200 ton widebody the next.

It's all about the cost of GSE.
Five conveyorbelts is a lot cheaper than five lower-deck loaders and a bunch of dollies. Bulkloading keeps cost down.