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Cyclic Hotline
9th Aug 2001, 03:40
Panel says air fuel tank measure too expensive

WASHINGTON, Aug 8 (Reuters) - A task force said on Wednesday it found that the use of inert or nonflammable gases in airline fuel tanks to help prevent explosions such as the one that brought down TWA Flight 800 was impractical and too expensive to implement in the near future.

The findings prompted renewed concern from disappointed U.S. safety investigators, who said efforts to prevent fuel tank explosions since the 1996 TWA jumbo jet crash that killed 230 people have not gone far enough.

After a year of study, the task force submitted its report to a Federal Aviation Administration advisory panel, which questioned some of the findings at a public hearing.

While the task force of experts from the aviation industry and other fields, as well as public interest groups, did not embrace the injection of inert gases to reduce the amount of air in fuel tanks, it said more study could yield a way to do it effectively, safely and more cheaply.

The FAA advisory committee, made up of industry and government officials and labor and consumer group representatives, ordered a 90-day review period before it would hold a final vote in November on whether to recommend the task force's findings to the FAA.

Two members of the advisory panel expressed fundamental reservations with the task force's findings.

"As it stands, I don't think it will have credibility," Paul Hudson, a committee member and executive director of the Aviation Consumer Action Project, said of the study.

PRICE TAG: $10 BILLION TO $21 BILLION

Hudson, the most outspoken of the study's critics, said he doubted calculations that developing and using inert technology could cost the aviation industry between $10 billion and $21 billion from 2005 to 2020.

He questioned whether the aviation industry, because of its major influence on the task force, played an unfair role in determining the bottom-line figures. "The costs are inflated," Hudson said at the hearing.

The National Transportation Safety Board also singled out the cost calculations for criticism.

"I am disappointed that their cost-benefit analysis leads them not to recommend inerting systems," Carol Carmody, the acting safety board chairman, said in a statement. "We question the factual basis for the cost-benefit analysis."

Task force co-chairman Bradford Moravec backed the analysis. "We tried to get the best expertise we could," he said. "I didn't feel this was a bunch of amateurs looking at this."

The study is considered a benchmark for consideration of new federal rules on fuel tank safety.

Two TWA explosion and other airline fuel tank blasts involving foreign-operated Boeing Co. (BA.N) 737 aircraft on the ground since 1990 also prompted closer scrutiny as well as industry and regulatory steps to avert future incidents.

Under regulations mandating the use of inert gases, aircraft manufacturers and airlines would have to find ways to redesign or modify fuel tanks and their systems. The changes would apply to airliners already in service, in or scheduled for production, or on the drawing board. Airports would have to make infrastructure changes to accommodate a new system.

OTHER STEPS ON FUEL TANK SAFETY

FAA spokeswoman Alison Duquette said the task force recommendation was only one factor the agency will weigh in considering whether to adopt a new rule.

Since the TWA disaster, aviation regulators have issued more than 40 mandates to prevent ignition sources in airliner fuel tanks. Those actions cover a wide range of aircraft, including the 747 and the popular 737 series aircraft.

The NTSB determined that Flight 800 was most likely destroyed by a center-fuel tank explosion shortly after takeoff from New York. While no firm conclusion was made on what triggered the blast, safety board investigators believe a wiring problem was to blame.

The safety board believes the FAA and the industry should take additional steps to further reduce the chance of an explosion by embracing the use of inert gas, like nitrogen, to eliminate air in fuel tanks.

But the task force said it could not find design concepts for ground-based or on-board systems that met regulations or provided a reasonable benefit for the money it would take.

An FAA regulation issued in May requiring aircraft manufacturers to review fuel tank system designs and airlines to develop new fuel tank maintenance strategies could affect up to 7,000 planes and cost the industry as much as $170 million.

But the NTSB said despite the aviation community's efforts so far, there is no way to be sure that all possible ignition sources have been eliminated. "The safety board strongly believes that near-term measures to eliminate flammable fuel tank vapors are necessary and prudent," Carmody said.

Squawk 8888
9th Aug 2001, 07:01
Given the rarity of inflight fuel-tank fires, if those cost estimates are accurate then a helluva lot more lives could be saved if that kind of money were invested elsewhere.

Just curious- I'm wondering why Explosafe technology (around since the 70s) hasn't been tried- it's simple, cheap and relatively maintenance-free. In a nutshell, it's a metal mesh inside the tank that dissipates heat pretty quickly- I saw a demo where a half-full jerry can had a flame burning in the spout like a candle. Won't prevent ignition, but does prevent explosions and slows the spread fuel fires. Was it proven less effective than the original claims, or was there some other reason?

Blacksheep
9th Aug 2001, 08:47
I think the NTSB are right to question the figures - they are clearly nonsense.

It would cost the industry very much more than a mere US$21 billion to inert every fuel tank in every aircraft AND provide the necessary infrastructure at every airport. We're talking about a hell of a lot of nitrogen here, not to mention an extra couple of thousand kilogrammes added to the weight of every aircraft. And what would the environmentalists have to say about it if it ever happened? We've already had to trash-can the most effective fire extinguishant available because of environmental concerns.

Nope, its not on and never was...

**********************************
Through difficulties to the cinema

Flight Safety
9th Aug 2001, 09:56
Just my two cents worth. The article reads in part:

But the task force said it could not find design concepts for ground-based or on-board systems that met regulations or provided a reasonable benefit for the money it would take.

Why is this?

The medical community has a technology available that uses an electrical means of separating the oxygen and nitrogen in normal air, and it's used to supply oxygen to patients. The units I've seen for a single patient are small (about the size and shape of a canister vacuum cleaner) and roll on wheels and plug in a normal electrical outlet just like a vacuum cleaner. The units have that typical green clear plastic tube for the oxygen outlet.

An aviation unit of this type (call it an "electric nitrogen generator") could produce a continuous supply of nitrogen using the same technology. I'm sure the process does not produce "pure" nitrogen, but the oxygen content might be low enough to provide effective fuel tank inerting. A system of this type with generator and lines, could be both light weight and very low maintenance, and perhaps not very expensive.

As a side benefit, the generator could be used to supply supplimental oxygen to the flight crew during a decompression event.

UNCTUOUS
10th Aug 2001, 01:17
If the FAA won't play ball with inerting, maybe there's another simpler way to stop the ullage filling with flammable vapours:


"c. There seems to have been little discussion throughout the TWA800 saga about the virtues or benefits of fuel additives to raise auto-ignition flash-points (page 41). I would have thought that any improvements in this area could be achieved without loss of calorific value per unit mass of fuel. And every step in the right direction helps disproportionately. An alternative to adulterating the whole fuel load in this way might be (for "at risk" a/c) simply to add a physically immiscible heavier fraction of distillate to the CWT that would still be less dense than the Jet A, float on top of residual fuel and suppress Jet A vapours (much as a thin layer of oil floating on water stops evaporation). The quite small quantities involved would mix well via downstream filtration, when pumped into the wing-tanks, HP pump-sprayed and then atomised into the combustion chamber - and so should not unduly affect the normal power-plant combustion process. "


The basic idea is that the additive would be required (to be added by the refuellers) once the temperature exceeded a given figure -30 deg celsius say (unless the CWT was to be at least half-filled - whereby the cooling heat-sink effect would then stop the underlying aircon packs from heating the fuel sufficiently to create a build-up of vapour). I would imagine that 25 US gallons would be enough to give a one inch top-layer of "damping" additive on the residual fuel in an essentially empty 747 CWT.

Mariner9
10th Aug 2001, 15:03
Surely a cheap & simple system would be to continually circulate the fuel from the centre tank to the wing tanks. As long as the fuel is maintained below the flash point (minimum 38C for Jet A-1) flammable vapours should not be generated.

Heavier distillates will invariably have a heavier density, and thus will not "float on top". Additionally, there would be problems with CFPP, freeze point, & MSEP of these materials.

Vfrpilotpb
10th Aug 2001, 16:00
Would'nt CO2 extracted from the engine's eflux do the same thing as Nitrogen, then it could be used to put a positive pressure in the tank therby taking away any possiblity of flamable fume build up, flames and sparks cannot live in CO2.

Flight Safety
11th Aug 2001, 06:00
An article from Air Safety Week

Issue: April 30, 2001

It worked. When it comes to inerting explosive vapors in fuel tanks, don't overlook the military's positive experience with liquid nitrogen (LN), argues a former U.S. Air Force officer. This method is not one of the options formally under consideration by a government-industry task force charged with recommending course of action to inert fuel tanks on transport-category aircraft (see ASW, April 16).

This former officer writes that the C-5A Galaxy transport, comparable in size to the B747, featured fuel tank inerting "as part of its stem to stern fire protection system." After an early crash, the entire C-5 fleet had been modified by 1977 with then state of the art optical smoke and fire detection systems, automatic Halon extinguishers in the manned areas, extra capability in the engine pylons and the LN system with fuel scrubbers, tank pressurization and wheel well protection.

"As a former C-5 AC (aircraft commander) I can tell you we LOVED our LN fuel scrubber and tank pressurization systems. Since we already required cryogenic LOX (liquid oxygen) servicing, all we really needed was a separate truck for the LN storage," he writes. "The problem was having to depend on other commands to maintain the basic truck, and I can remember that the LN servicing truck at Torrejon AB in Spain was out of service for months because mechanics could not obtain repair parts."

"We were never supposed to turn off the tank pressurization system, but we would routinely do so because we wanted to preserve our on board LN supply for critical legs going 'down range' and back to Southwest Asia or Africa, since we knew we couldn't get serviced in Spain," he added.

"On board liquid nitrogen inerting perhaps is not the solution for today's aircraft," he opined. New on-board inert gas generating system (OBIGGS) technology may be preferred, as it eliminates dependency on ground support (Indeed, Safety Board officials pointed to the OBIGGS on the F-22 fighter as the kind of example the airline industry could pursue). Of course, a modernized LN technology might be competitive, given its potential to protect a 747-size aircraft for up to three flights.

"Back in the OLD days," this Air Force pilot recalled, "LN dewars worked reliably and saved at least one airplane (at Travis AFB in the mid-1970s) from an onboard fire. That one SAVE paid for the modification of the entire C-5A fleet." By the way, in this application not only was the ullage "washed," the fuel itself was "scrubbed" by percolating nitrogen up from the bottom of the tank. Scrubbing and pressurization take care of empty, partially full and full tanks. The ARAC has rejected fuel scrubbing as not cost effective.

Based on his experience, this former Air Force officer offered two reasons for action:

"Fuel inerting is a necessity well past its due date and, like smoke detectors for Class D belly compartments, we need to get on with it and get fuel tanks inerted." "The most important action that government, industry and air carriers can take is to catch up with the fire protection that has been airborne on the C-5A for almost a quarter of a century."

The OBIGGS system described here is the system I refered to earlier.

"On board liquid nitrogen inerting perhaps is not the solution for today's aircraft," he opined. New on-board inert gas generating system (OBIGGS) technology may be preferred, as it eliminates dependency on ground support (Indeed, Safety Board officials pointed to the OBIGGS on the F-22 fighter as the kind of example the airline industry could pursue).

Here are a couple of links to the OBIGGS technology.
http://www.airliquide.com/ww/chapter02/medal/en/obiggs.htm
http://www.airproducts.com/prism_membranes/page02.asp

[ 11 August 2001: Message edited by: Flight Safety ]

GlueBall
12th Aug 2001, 03:38
It's interesting to note that in the TG 73 empty CWT explosion, the center tank pump was running. And the packs were running at max for 40 minutes at the jetway in 93F OAT.
That airplane was 8 years old.

In 1991 a PAL 73 CWT exploded during pushback under similar conditions. That airplane was less than one year old.

Not safe to have a 115VAC pump running inside a dry tank. A Boeing design flaw.

On the DC-8 the center tank pump is inside the No.2 Main tank, a fail safe design.

The best thing to do is to pull the CWT pump CB when the tank is empty.

Stay alive. :cool: