From: Terry W. Colvin (fortean1@mindspring.com)
Date: Thu May 30 2002 - 13:59:56 MDT
On Monday 27 May 2002 04:50 am, eva durant wrote:
> Don't airplane age? Shouldn't be a time limit as surely there are
> eventual failure after 20+ years? What do they check when they do
> checks?
Of course airplanes age. The U.S. Air Force as we speak is flying B-52
Stratofortresses which are, IIRC about 40 years old (the Air Force is
currently flying only B-52Hs, and the H model production run extended from
May 1961-October 1962).
In the United States, Federal Aviation Administration regulations mandate
periodic (I believe yearly, though it might be more frequent) airworthiness
inspections of both the airframe and powerplant, and any component which
appears to be close to failure is replaced or repaired, or else the aircraft
is deemed not airworthy, and it is not permitted to be flown. In the general
aviation sector (private, non-commercial aircraft) it's not uncommon to see
aircraft over 50 or 60 years old still airworthy and flying.
Len Cleavelin
------------------
Some aircraft carry their age remarkably well. For example, there are
still plenty of DC3s (C54) flying around the world, first built in the
early 1930s and the last one of which was built during WWII. Many Air
Forces are still using C130 Hercules which I first rode in in the early
1960s, though of an earlier Mk than those currently in service. Major
airlines flying Boeings and Airbuses tend to retire their aircraft at 20
years, though these are often bought by charter and minor airlines and I
wouldn't be at all surprised if many of the accidents happen with the older
airframes.
Barry Williams
the Skeptic of Oz
---------------------
Strictly speaking, under the "nuclear triad" doctrine missles weren't
officially considered the method of choice, even though two thirds of the
triad (manned bombers, land based intercontinental ballistic missiles, and
submarine launched ballistic missiles) were missiles. My recollection is that
during the Cold War a certain proportion of the strategic bomber fleet was
kept in alert status at all times. What proportion of those bombers were
actually airborne, and what proportion were on the ground but capable of
being airborne in some suitably small time period (I think 5 minutes or so
was the stated figure) escapes me right now.
I'm not aware that the Air Force keeps strategic bombers on such stringent
alert status anymore, but that change in posture has been more a function of
the end of the Cold War than a function of a preference for missiles as
delivery vehicles, I think.
Len Cleavelin
--
Green Lantern: So you're saying a gorilla *talked* to you?
Flash: Hey, we both have a Martian's phone number on our speed dial.
I think I deserve the benefit of the doubt here.
--"Justice League" [TV show]
-----------------
>I don't know - didn't the US have a policy of keeping a certain percentage
>of tactical bombers in the air at all times?
Yes. They discontinued that sometime in the 80's, IIRR. The "Looking Glass"
airborne command center planes flew 24/7 until about 1996, and I'm sure
that they keep AWACS planes aloft constantly around places like Iraq and
Afghanistan.
Most military planes are designed to be refueled in the air, so multiday
missions are common.
But length of time aloft is not really the problem, pressurization cycles
are what put the most wear on an airframe (well, other than dogfighting).
When an aircraft on the ground, the air pressure inside and outside the
plane are equal. When it climbs to altitude, the air pressure inside is
MUCH greater than that outside (assuming it's a pressurized plane, of
course), and the airframe bulges outward. When the plane comes down, the
frame relaxes again. It's that cycling of flexing and relaxing that really
stresses the plane. That was what caused the Aloha Airlines failure: the
plane was used for a LOT of short hops, and the fuselage just became too
fatigued.
Dave Palmer
--------------------
I think they called them "strategic" bombers ("Strategic Air Command" and
all that)... :-) And yeah, they stopped having them constantly flying
sometime in the 1960's, I believe. Although they DID keep B-52s loaded with
nukes sitting on the runways, ready to fly right up until the early 1990's.
I live just a few miles from Castle AFB, one of the B-52 bases from the cold
war. It's been closed for a few years now, but I can remember taking a tour
of it once and the guide told us to please not take pictures of a certain
building (a low bunker in the side of a hill), because that was one of the
storage points for nuclear weapons, and the security people didn't like
that. Those B-52s are just monstrously big, too. It's a cliche to say it,
but when you're standing on the runway next to one, you just can't believe
that thing can fly. The wings are so broad they actually droop... During
the Gulf War, there were newspaper articles here that said some of the B-52s
from Castle would take off here in California, fly to Iraq, bomb the
Republican Guard positions, and then land in Diego Garcia in the Indian
Ocean...
Kevin P. France
---------------------
Not necessarily. Military pilots do lots and lots of training. I used to
work in San Bernardino near the (now closed) Norton Air Force Base. I
believe the base's former role was supplies & logistics, and they had a
bunch of cargo planes there. I think they were C130s, but I'm not sure.
Anyway, there was always at least one of them flying circles around the San
Bernardino Valley, doing "touch and go" landing/takeoffs. That is, the pilot
brings the plane in on a landing approach, lowers the wheels etc., touches
down on the runway, then immediately switches into takeoff mode, launches
the thing back off the runway, and makes another circle. I understand that
these are very hard on airplanes, because during landings and takeoffs the
weight of the plane shifts from the wings to the wheels and vice-versa.
(sort of like the pressure shifts Dave explained).
My office was almost right beneath the landing approach. It was just amazing
to look up and see these things slowly coasting in. Nowhere near as big as
the B52s Kevin talked about, but it always struck me that nothing that big
should really be able to fly, and it ought to just fall like a rock.
Sometimes the planes had awful sounding engines that sounded like they
needed new bearings or something. Always made me nervous.
-SW
----------------------
My recollection is that pilots are under a duty to rack up a certain number of
flight hours per month in order to maintain their qualifications. Not to
mention the added incentive of not wanting to lose their flight pay.
Len Cleavelin
----------------------
They are required to put in the hours. But probably not as many hours as
airline
pilots. Fighter pilots, especially. Fighters are expensive to fly and
maintain.
And dangerous.
I recall working on the fighter flight line in the Navy. The jets spent most of
their time parked. Like 90% or more. Go out to an airport. A jetliner pulls
up
to the gate, and about an hour and a half later it's off again for another long
flight. Commercial jets make money in the air. Military jets save taxpayer
money
on the ground.
At sea it seemed there was a lot more flying. Every day there was good weather
(except an occasional day off) there were flight operations involving about 75%
of the squadrons' aircraft. Now that's dangerous.
Bomber pilots I don't know too much about. I doubt if B1s spend a large part of
their lives in the air.
John Blanton
--
Terry W. Colvin, Sierra Vista, [Cochise County] Arizona (USA)
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