Hi Pootz,
What an interesting question! A loop, as you may or may not know, is
what is known as an "aerobatic" maneuver. The FAA defines an
aerobatic maneuver as “an intentional maneuver involving an abrupt
change in an aircraft's attitude, an abnormal attitude, or abnormal
acceleration, not necessary for normal flight.” Title 14 CFR. FAR Part
91.303 ( http://ecfrback.access.gpo.gov/otcgi/cfr/otfilter.cgi?DB=3&query=14000000091®ion=BIBSRT&action=view&SUBSET=SUBSET&FROM=1&SIZE=10&ITEM=1
) and restricts who, what, when and where they may be performed.
The inside loop is one of the most basic of aerobatic maneuvers, and
is actually one of the least stressful of aerobatic maneuvers,
requiring a maximum of about a 3-4 (positive) G pullup on entry, and a
second or two of 0 G on the resulting dive and pullup. A good
description of how to execute a loop is here:
http://acro.harvard.edu/ACRO/acro_figures.html#loop
To give you a little perspective, most single-engine aircraft, for
example, such as Cessnas or Pipers, are certified in what’s known as
“utility category.” Even though this means they are not built
specifically for aerobatic flight, they are approved for maneuvers
such as spins, and designed (within limitations) to withstand flight
load factors of 3-8 negative G’s and up to 4.4 positive G’s. You can
see this is well within the envelope for performing a loop, though I
probably wouldn’t try one in a C-172! But what this demonstrates is
that most aircraft are sturdily built and designed to withstand
stresses in excess of their normal expected operations.
This is also generally true in the case of airliners. Just flying
through significant turbulence can greatly increase the load factor,
or stress on aircraft, and they have to be (and are) built to take a
lot of it. However, so many factors go into determining G-load
limitations, it would be difficult to envision every possibility. For
example, calculating flight load factors (on which G limits are based)
is a complicated business depending on total number and weight of
passengers, amount and location of cargo and fuel, maneuvering speed,
acceleration, and many other considerations.
The approved flight manuals (AFM) for these aircraft, might give
detailed information on specific operating limiations and
calculations, but I was unable to find either one online, though that
isn’t surprising. These are very large books, and are usually very
expensive to purchase. It’s not common to find free editions of any
flight manuals for most aircraft. However, here is a page of specs
for the Airbus A380 http://www.aerospaceweb.org/aircraft/jetliner/a380/index.shtml
, which states that the G limits for this aircraft are unknown. The
same is true for the B727. Read its specs here:
http://www.aerospaceweb.org/aircraft/jetliner/index.shtml What this
really means is that it was likely not considered a necessity during
flight testing to determine absolute G-load limitations, or that it
was not possible to determine these with any accuracy because of the
high number of potential configurations. If you would like to read
the specs on more airliners, you might find one/some which do state
their load limits. An extensive list is available here:
http://www.aerospaceweb.org/aircraft/jetliner/index.shtml )
What all this boils down to with respect to your questions is, on the
surface, no, it would not be a good idea to execute any aerobatic
maneuver in any passenger airliner, especially one loaded with
passengers and cargo, and one would likely be risking a crash.
However, yes, it could theoretically be possible to safely fly a loop
in one. For example, if there were a threat that the entire aircraft
and all its passengers and crew might be lost, and the execution of
such a maneuver could possibly avert such a disaster, as in overcoming
one or more armed terrorists by throwing them around the plane, then
yes, it would certainly be worth a try and could very well succeed
without necessarily crashing and/or permanently damaging the aircraft.
A less dramatic maneuver might also accomplish the purpose, such as an
abrupt entry to a steep turn, or a chandelle, which is a standard
high-performance climbing turn.
Here are a few more of the best aviation information sites for you to
check out for additional information if you’re interested in learning
more:
http://www.landings.com (general info)
http://www.aviationnow.com/ (general info)
http://www.monmouth.com/~jsd/how/htm/title.html#mytoc (overview of
aerodynamics)
http://acro.harvard.edu/ACRO/faq_aerobatics.html (aerobatics)
http://www.faa.gov/ (FAA main site)
http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14tab_00.html
(current regulations)
I hope this gives you a better understanding of the factors involved
in flying a loop in any aircraft, including an airliner. Search
terms I used (drawing on my own knowledge as a certificated Commercial
pilot) included:
B727 (or Airbus A380) g-limits
limitations B727 (or Airbus A380) operating OR performance
B727 (or Airbus A380) load factors OR limitations
B727 (or Airbus A380) operating instructions
aerobatics
aerobatic maneuvers
Best wishes,
Byrd |
Clarification of Answer by
byrd-ga
on
30 Oct 2002 06:15 PST
Yes, well, ahem, that is, I have heard some talk amongst other pilots,
hangar talk you know, entirely off the record, just casual airport
conversation you understand, that might possibly lead one to be
inclined to believe that such a maneuver has been tried and lived
through, maybe on a training flight, or perhaps a deadhead returning
from somewhere or other. However, I don't know anything else about
that, except that sometimes in simulator training pilots attempt
maneuvers they wouldn't dare try in a real aircraft.
As far as official documentation of an airliner performing a loop, a
search of the NTSB database of aviation accidents/incidents turned up
nothing involving the two aircraft in your original question. A
search of the database for all aircraft, though, using only the word
"loop" as a keyword, gave 170 returns, of which a total of four were
scheduled airliners. This does not necessarily mean that any of them
flew a loop; the word might be used in some other context. One would
have to study the entire report to know for certain. These are
voluminous documents, but if you'd like to read them, the full text is
available for free. The site won't let me post a link to the exact
search results, so if you'd like to read them, go to the search page
here http://www.ntsb.gov/ntsb/query.asp#query_start , check "airplane"
for aircraft category, "no" for amateur built, and enter "loop" as
keyword. No need to fill in anything else. The main site for the
NTSB's aviation section is here:
http://www.ntsb.gov/aviation/aviation.htm
There is one other thing to keep in mind if you'd like to search these
databases. Aviation is full of esoteric language, and furthermore,
the NTSB is famous for using convoluted euphemisms to describe
circumstances. For example, a plane that flew a loop and crashed,
could be described as having flown a "prohibited maneuver," or having
entered "an unusual attitude," or demonstrating "abrupt movement of
the control surfaces." One has to study the report and quite
literally read between the lines sometimes to ascertain exactly what
occurred.
In addition to the NTSB, there is a procedure for pilots and others to
report unusual occurrences without fear of prosecution by the FAA or
NTSB for license violations or other repercussions. It's run by NASA
and known as the Aviation Safety Reporting System or ASRS
(http://asrs.arc.nasa.gov/database_nf.htm ). “The [entire] ASRS
Database is not available on-line within the ASRS site. A version of
the ASRS Database may be accessed from the FAAs Office of System
Safety NASDAC site at http://nasdac.faa.gov/asp/asy_asrs.asp .” At
this site, a similar search of this limited online database on “air
carrier,” keyword “loop” yielded 724 returns, but with no details
provided. "Requestors for ASRS Database information or records from
ASRS should submit their request with an explanation for the purpose
of their request to:
NASA Aviation Safety Reporting System
Attention: Database Information
P.O. Box 189
Moffett Field, California 94035-0189 ”
In addition to accident reports, a general search of the web turned up
no news or other reports of an airliner specifically performing a
loop. Although I can't definitively say without question that it has
never been done or been reported being done, it does appear highly
unlikely, at least in the United States or by US registered aircraft.
If you would like a researcher to undertake a more in-depth global
search on this additional topic, you might want to consider posting it
as a separate question. I do hope this extra information has been of
use to you, and I will post should I come across anything additional.
Search terms (other than NTSB search query):
jet airliner loop
://www.google.com/search?num=50&hl=en&lr=&ie=UTF-8&oe=UTF-8&as_qdr=all&q=%2Bjet+%2Bairliner+%2Bloop&btnG=Google+Search
jet airliner unusual attitude
://www.google.com/search?num=50&hl=en&lr=&ie=UTF-8&oe=UTF-8&as_qdr=all&q=%2Bjet+%2Bairliner+%2Bunusual+attitude&btnG=Google+Search
jet airliner aerobatic maneuvering
://www.google.com/search?num=50&hl=en&lr=&ie=UTF-8&oe=UTF-8&as_qdr=all&q=%2Bjet+%2Bairliner+%2Baerobatic+%2Bmaneuvering&btnG=Google+Search
Best wishes,
Byrd
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