FAA Grounds 787s
How will the carbon fibre aircraft cope with any large electrical input like a lightening strike ? What mitigation is included or are pilots
supposed to avoid weather in these planes ?
supposed to avoid weather in these planes ?
The industry learned that one a while back.
IIRC there's a wire mesh imbedded in the skin.
pattern of senior people aboard first flights continues
Originally Posted by FlightPathOBN
United 787 UAL-1 flight today..just pushed back KIAH -KORD
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"Boeing is taking a multilayered approach to lightning protection of the 787 fuel tank:
• The initial lightning strike must be dispersed quickly around the airframe to prevent concentrated damage. Also, the airplane's electronic flight instruments must be shielded from disruption by the intense electromagnetic field. To accomplish this, Boeing will embed a thin metal mesh or foil in the outer layers of the composite fuselage and wings.
• A slight gap between a wing-skin fastener and the hole it goes into could be a source of sparking as current jumps the gap. Boeing will install each fastener precisely and seal it on the inside to ensure a snug, spark-free fit.
• Inside the wings, any gap along the edges where wing skin meets internal structural spars could cause a spraying out of electrons in a lightning strike — a phenomenon called "edge glow." Boeing will seal the edges with nonconducting goop or glass fiber.
• And, in case the efforts to shut out ignition sources fail, Boeing will install a nitrogen-generating system (NGS) that reduces flammable vapor in the wing tanks by filling the space above the fuel with inert gas.
Last November one safety team became concerned that Boeing was relying too heavily on tight, precise installation of the fasteners. It worried that a loose fastener could not be detected after construction.
"The latent failure of any one fastener leaves the airplane one event away from a catastrophic incident" caused by a spark, the team's safety review stated.
The team recommended making the NGS system "dispatch critical," meaning the airplane is not allowed to take off if the nitrogen system isn't functioning.
The team was praised for "unwavering determination" in pursuing its solutions to the lightning-safety issues "despite the unpopularity of this position with others" — but its view did not prevail.
"We don't have to make it flight critical," Gillette said.
Gillette said this kind of debate is common among engineering teams.
"These are really strongly held opinions by really bright people," Gillette said. "It's almost like politics — once you believe in a solution, you really believe in it."
Gillette said that back in November the fasteners were not working as required — some were pulling right through the skin.
But Boeing adjusted the fastener design and installation process. And to test for loosening of the fasteners, Mitsubishi Heavy Industries, which is making the wings, has shaken skin panels through the equivalent of one and a half airplane operating lifetimes.
Extensive tests on fastener installation will be completed within weeks, Gillette said.
FAA regulations demand a cold statistical outcome: The 787 design has to ensure that the chance of lightning sparking a fuel-tank explosion in flight is less than one in a billion.
Gillette said the NGS system is expected to operate at least 97 percent of the time, but the safety systems combined will assure the 787 exceeds the one-in-a-billion probability target.
"It is not a good idea to put all your eggs in one basket," he said."
Gillette said the NGS system is expected to operate at least 97 percent of the time, but the safety systems combined will assure the 787 exceeds the one-in-a-billion probability target.
"It is not a good idea to put all your eggs in one basket," he said.
note: the Safety Team's view did NOT prevail???
• The initial lightning strike must be dispersed quickly around the airframe to prevent concentrated damage. Also, the airplane's electronic flight instruments must be shielded from disruption by the intense electromagnetic field. To accomplish this, Boeing will embed a thin metal mesh or foil in the outer layers of the composite fuselage and wings.
• A slight gap between a wing-skin fastener and the hole it goes into could be a source of sparking as current jumps the gap. Boeing will install each fastener precisely and seal it on the inside to ensure a snug, spark-free fit.
• Inside the wings, any gap along the edges where wing skin meets internal structural spars could cause a spraying out of electrons in a lightning strike — a phenomenon called "edge glow." Boeing will seal the edges with nonconducting goop or glass fiber.
• And, in case the efforts to shut out ignition sources fail, Boeing will install a nitrogen-generating system (NGS) that reduces flammable vapor in the wing tanks by filling the space above the fuel with inert gas.
Last November one safety team became concerned that Boeing was relying too heavily on tight, precise installation of the fasteners. It worried that a loose fastener could not be detected after construction.
"The latent failure of any one fastener leaves the airplane one event away from a catastrophic incident" caused by a spark, the team's safety review stated.
The team recommended making the NGS system "dispatch critical," meaning the airplane is not allowed to take off if the nitrogen system isn't functioning.
The team was praised for "unwavering determination" in pursuing its solutions to the lightning-safety issues "despite the unpopularity of this position with others" — but its view did not prevail.
"We don't have to make it flight critical," Gillette said.
Gillette said this kind of debate is common among engineering teams.
"These are really strongly held opinions by really bright people," Gillette said. "It's almost like politics — once you believe in a solution, you really believe in it."
Gillette said that back in November the fasteners were not working as required — some were pulling right through the skin.
But Boeing adjusted the fastener design and installation process. And to test for loosening of the fasteners, Mitsubishi Heavy Industries, which is making the wings, has shaken skin panels through the equivalent of one and a half airplane operating lifetimes.
Extensive tests on fastener installation will be completed within weeks, Gillette said.
FAA regulations demand a cold statistical outcome: The 787 design has to ensure that the chance of lightning sparking a fuel-tank explosion in flight is less than one in a billion.
Gillette said the NGS system is expected to operate at least 97 percent of the time, but the safety systems combined will assure the 787 exceeds the one-in-a-billion probability target.
"It is not a good idea to put all your eggs in one basket," he said."
Gillette said the NGS system is expected to operate at least 97 percent of the time, but the safety systems combined will assure the 787 exceeds the one-in-a-billion probability target.
"It is not a good idea to put all your eggs in one basket," he said.
note: the Safety Team's view did NOT prevail???
Last edited by FlightPathOBN; 20th May 2013 at 21:22.
"It is not a good idea to put all your eggs in one basket," he said."
Still not going to fly on one, yet.
Usual disclaimers apply!
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There is nothing new about any of that. All a/c have to confirm to SFAR88 and the CDCCL (Airbus FAL) items during manufacture AND maintenance!
Loose fasteners could occur on a metal skinned airframe as well. The reasons for a tight installation is for ultimate mechanical strength and to prevent a fuel leak as much as bonding. Also the finished installation is cap sealed. Any PD between the fastener the skin and the collar/nut is fully enclosed.
The 787 with its CRFP wing is no different in that respect. The only thing of note is the 'tiger striping' on the wing planks to ensure a safe conductive path through to the wing root. This is also there to prevent the skin internal finish from failing and exposing the CRFP if there were to be a strike.
Loose fasteners could occur on a metal skinned airframe as well. The reasons for a tight installation is for ultimate mechanical strength and to prevent a fuel leak as much as bonding. Also the finished installation is cap sealed. Any PD between the fastener the skin and the collar/nut is fully enclosed.
The 787 with its CRFP wing is no different in that respect. The only thing of note is the 'tiger striping' on the wing planks to ensure a safe conductive path through to the wing root. This is also there to prevent the skin internal finish from failing and exposing the CRFP if there were to be a strike.
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The team recommended making the NGS system "dispatch critical," meaning the airplane is not allowed to take off if the nitrogen system isn't functioning.
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There is nothing new about any of that. All a/c have to confirm to SFAR88 and the CDCCL (Airbus FAL) items during manufacture AND maintenance!
Loose fasteners could occur on a metal skinned airframe as well. The reasons for a tight installation is for ultimate mechanical strength and to prevent a fuel leak as much as bonding. Also the finished installation is cap sealed. Any PD between the fastener the skin and the collar/nut is fully enclosed.
The 787 with its CRFP wing is no different in that respect. The only thing of note is the 'tiger striping' on the wing planks to ensure a safe conductive path through to the wing root. This is also there to prevent the skin internal finish from failing and exposing the CRFP if there were to be a strike.
Loose fasteners could occur on a metal skinned airframe as well. The reasons for a tight installation is for ultimate mechanical strength and to prevent a fuel leak as much as bonding. Also the finished installation is cap sealed. Any PD between the fastener the skin and the collar/nut is fully enclosed.
The 787 with its CRFP wing is no different in that respect. The only thing of note is the 'tiger striping' on the wing planks to ensure a safe conductive path through to the wing root. This is also there to prevent the skin internal finish from failing and exposing the CRFP if there were to be a strike.
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The reasons for a tight installation is for ultimate mechanical strength and to prevent a fuel leak as much as bonding. Also the finished installation is cap sealed. Any PD between the fastener the skin and the collar/nut is fully enclosed.
A slight gap between a wing-skin fastener and the hole it goes into could be a source of sparking as current jumps the gap. Boeing will install each fastener precisely and seal it on the inside to ensure a snug, spark-free fit.
I would be very concerned about the isolation of the grounding system. This was one of the problems noted with the battery issue on the aircraft already....
Last edited by FlightPathOBN; 21st May 2013 at 18:51.
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New IATA Li ion batteries cargo policy
Guys, have you heard IATA changed their safety policy regarding Li ion batteries transportation. (cellphones, ipads, ....you name it) this will be very costly!!. The reason : Industry concern with li ion batteries.
Smells like a scapegoat for boeing faulty design. Seems Now we ALL will have to pay for them, wether we fly the 787 or not. What do you think?
Smells like a scapegoat for boeing faulty design. Seems Now we ALL will have to pay for them, wether we fly the 787 or not. What do you think?
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Kinda sad that in what must be an "on our very best behavior" high-visibility period for Boeing stuff like this still happens. If a specialist team can't do better than that, how do the daily grunts on the production line cope with a 50%-increased production rate? Overtime, lots of new hands.
mods complete
Guy Norris reports on the Aviation Week blog that the 50th and last battery system update for previously delivered 787s is complete.
Norris blog post on 787 updates
Norris blog post on 787 updates
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as a result of the added titanium wires for lightning strike, strengthening tabs for wings and tail assemblies, wingbox additions, and the battery boxes, the MTOW now allows for 2 passengers per aircraft...
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Latest AW&ST p.35 says 787 APU overheats due to inlet door closing after shutdown. It also ties this to rotor bowing, causing vibes on restart.
Bowed rotor has been discussed previously on Pprune - and can happen on any turbine (e.g. APU) but seems to me this is independent of APU overheat.
Bowed rotor has been discussed previously on Pprune - and can happen on any turbine (e.g. APU) but seems to me this is independent of APU overheat.
online AWST article with APU issues
I don't have my print copy yet so can't compare this to the p.35 version, but suspect AWST online APU article has highly related APU content.
It asserts that there are procedural workarounds to avoid the problem at some cost and inconvenience, with forthcoming improvements intended to stop the need for the special procedures.
It asserts that there are procedural workarounds to avoid the problem at some cost and inconvenience, with forthcoming improvements intended to stop the need for the special procedures.
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A well written article on 787 battery issue.
Avionics Magazine :: System Design: Fixing the 787?s Batteries
Avionics Magazine :: System Design: Fixing the 787?s Batteries