New Details About DL 737-700 Incident

[Falcon900flyer 0]

Greetings,I just spoke with a friend of mine who's a Lead Mechanic for Delta in ATL. He told me that the news media was totally incorrect in saying the "brakes failed" on the airplane. What really happened was that the parking brake was set and the throttles were advanced to full power. (Apparently, the aircraft was in maintenance for a scheduled fan lube. The work was completed and the aircraft taxiied out to the run-up pad for leak-check, etc). Once the maintenance tech(s) noticed they were moving, they retarded the throttles to idle. By then, they had already skidded over 300' and we all saw what the end result was. At the time of the incident, the ramp was wet and the aircraft was of course, very lightly loaded. The aircraft was not chocked (as they normally don't chock aircraft for an engine run-up, but perhaps they may start now). The FAA was on scene after the incident and noticed the tires left skid marks for the full distance it travelled. (Since the parking brake was set, anti-skid is not available). The skid marks started out dark black then went to a lighter black color, followed by dark black. The FAA said that the reason for the lighter black color was apparently the aircraft went fast enough to put some load on the wings and take some weight off the wheels. The FAA concluded that the aircraft hydroplaned. (I find this interesting because the aircraft would have to be travelling at a high speed for this to happen. Hydroplane speed is calculated as 9 * the square root of the tire pressure. Perhaps the aircraft taxiied through grease or oil or jet fuel and coupled with the wet ramp, produced a very slick condition for the aircraft to skid). Guess that just goes to show you how much power those CFM's put out! Just my .02 worth...John

[MrKen 3]

Not to mention hydro planing leaves no skid marks. It's likely just a generic layman explanation.

[Falcon900flyer 0]

Greetings,I left out the aircraft was lifted up by crane, placed back on pavement,and tugged back to the maintenance hangar on its own landing gear. I was told that there is "minimal" damage to the aircraft. I would've figured at the very least, the #1 engine would need a complete tear-down and inspection, perhaps a new radome, and new nosegear doors. John

[ajpongress 467]

He told me that the news media was totally incorrect in saying the "brakes failed" on the airplane.

The media was wrong?! Impossible!.....Anything to get a story these days....facts are now manufactured.

[simbio 56]

So if I understand the aircraft became an hovercraft, but with accident like that who is going to pay the insurance or delta ?

[Fabo 213]

My best bet is they would have insured for maintenance mishaps.

[dmwalker 612]

 

apparently the aircraft went fast enough to put some load on the wings and take some weight off the wheels.

So just how fast can a 737 go with the parking brake on?

[WR269 367]

Brings back memories of the Tolouse accident with the brand new Etihad A340-600.Would be interesting to know the pressure difference between parking brake and normal toe brakes. One of the recommendations that came out was to never do a max power ground engine run on all engines simultaneously!

[G550flyer 1,029]

I find it interesting that you say they took both engines to power. I've done a few thrust rating checks and only advanced one throttle at a time to see if they will make the calculated N1. I must admit as a pilot that I haven't chocked the plane during run ups, but Usually Mx do.Very interesting that they didn't notice the movement. I've had the plane move forward on a icy runways while setting power prior to brake release and it was very evident. You have to be very vigilant when ever you have an engine at high power settings.

[G550flyer 1,029]

Would be interesting to know the pressure difference between parking brake and normal toe brakes.

In most aircraft you get the same amount "3000psi". In the heavies that i flew, you actually applied the toe brakes and locked them in position with the parking brake lever. In the gulfstreams, the parking brake is separate and supplied by a 3000psi emergency brake accumulator. As long as there is regular system pressure, the parking brake will supply 3000psi. With out sys press, the pressure bleeds off giving a minimum of 5 to 6 parking applications.

[JRBarrett 3,121]

 

In most aircraft you get the same amount "3000psi". In the heavies that i flew, you actually applied the toe brakes and locked them in position with the parking brake lever. In the gulfstreams, the parking brake is separate and supplied by a 3000psi emergency brake accumulator. As long as there is regular system pressure, the parking brake will supply 3000psi. With out sys press, the pressure bleeds off giving a minimum of 5 to 6 parking applications.

On the GIV, we always run the aux pump to bring the pressure up to 3000 before setting the parking brake. I assume the 550 is similar. Many aircraft cannot be held by the brakes with both engines at full power under the best of circumstances. I almost had a "Delta moment" while investigating a pilot's complaint that one engine was surging while setting takeoff power on a 58P Beech Baron. The 58P has turbocharged TSIO520 engines that can develop 45 inches of manifold pressure at full throttle. With the (new) brakes fully set, I slowly brought both engines up to takeoff power simultaneously. As soon as the turbos kicked in, the aircraft started moving forward. I immediately throttled back. Thought the brakes were slipping, but when I turned the plane around to taxi back, there were two black skid marks where the mains had been sitting.Brand new brakes, brand new tires, and a perfectly dry concrete ramp, and still the engines had enough power to literally drag the locked tires across the surface. The aircraft was very light, with only half-full fuel tanks, and just me aboad, which probably contributed...

[G550flyer 1,029]

On the GIV, we always run the aux pump to bring the pressure up to 3000 before setting the parking brake. I assume the 550 is similar.

Yep, in the 5 and 550 we call it the sat night fever dance. hand to your thigh(parking brake), finger to the ceiling(aux pump switch on the overhead panel). The regular sys press i was speaking of was the aux sys. It's the same way on the G3, flew those too lol. Interesting that they didn't also plumb the accumulator to the left sys with a check valve. Just odd to have to charge the accumulator every single time you set the parking brake regardless of engines running or not. I guess im still big jet minded.

[JRBarrett 3,121]

Yep, in the 5 and 550 we call it the sat night fever dance. hand to your thigh(parking brake), finger to the ceiling(aux pump switch on the overhead panel). The regular sys press i was speaking of was the aux sys. It's the same way on the G3, flew those too lol. Interesting that they didn't also plumb the accumulator to the left sys with a check valve. Just odd to have to charge the accumulator every single time you set the parking brake regardless of engines running or not. I guess im still big jet minded.

Ah. it's the Gulfstream Way! Like having the Abex generator in the wheel well kick on with a loud howl for a few seconds if you power down the electrics before hydraulic pressure in the combined sytem is fully depleted. The first time I heard that, I was standing right next to it pinning the gear. Stood up so fast that I smacked my head on the wing...

[quadraspleen 7]

Very interesting that they didn't notice the movement.

They were only grease monkeys..I don't expect they train them up in noticing forward movement :(

[Fabo 213]

I can imagine them not noticing if they were concentrating on engine indications...