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Aircraft Corrosion
Clear Water Rinse Systems Mitigate Risk and Reduce Maintenance Costs

SITUATION: Corrosion – the natural deterioration of metal when it reacts with various environmental conditions – is a costly,
hazardous problem that affects every sector of the economy, including consumer products, utilities, construction, and transportation.
It is a particular challenge in commercial and military aviation, where corrosion compromises safety and performance, erodes
productivity, and adds signi cantly to the cost of aircraft maintenance.

Corrosion can render an aircraft un-airworthy by weakening structural components, roughening the outer surface, loosening fasteners,
hastening cracking, and facilitating the entry of water into electronic xtures. Left untreated, corrosion can hasten other conditions that will
eventually cause structural failure. Corrosion can quickly develop in key areas, where loss of even a small degree of material integrity can allow
moisture, salt, sand, and other contaminants to enter, sometimes with catastrophic results. The crash of an El-Al Boeing 747 in Amsterdam
(1992), the crash of a China Airlines Boeing 747-200F (1991), and the incident in 1988 in which a hole was torn in the fuselage of an Aloha
Boeing 737 as it ew over Hawaii were all traced to structural damage caused by corrosion.

Corrosion can affect entire eets of aircrafts, causing delays and compromising military
readiness:

The crash of a 28-year-old F-15C Eagle ghter in Virginia in 2014 and the break-up of another F15-C over Missouri in 2007
focused attention on the aging of the U.S. Air Force’s eet of ghters, bombers, and tanker aircrafts. Concerns about metal fatigue
and corrosion forced the grounding of the entire F-15 eet during the investigation of the 2014 incident, and prompted placing F-
15Es on ground alert while ying missions in Iraq and Afghanistan with other aircrafts.
Nearly one of every ve of the Marine Corps’ aircraft – as many as 134 aircrafts, including F/A-18 Hornets, CH-53E Super Stallions,
AV-8B Harriers, MV-22B Ospreys, and H-1 Hueys – were grounded in early 2015 due to high levels of corrosion.
Over many years, problems with the cabin pressurization system in the U.S. Air Force’s C-130 aircraft had severely sickened pilots
and crews and grounded many of the aircraft, causing costly delays. The problem was eventually traced to corrosion of a critical
part.

Aircrafts are particularly vulnerable because they are constructed from a variety of metals that are subject to different types of corrosion, and
because they are constantly exposed to corrosive environmental conditions.
Other factors – including the age of the plane, where it is operated, how often it is cleaned, and whether it is hangared – will also affect how
quickly and to what extent corrosion will develop.
ENVIRONMENTAL FACTORS
Corrosion occurs when a metal forms a chemical reaction with its environment, resulting in the oxidation, and eventual breakdown, of the
metal. In aviation operations, both on the ground and in the air, speci c environmental factors and the presence of certain substances make
conditions right for corrosion to develop.
Atmospheric and environment conditions are the primary cause of corrosion, and they hasten the process once it has begun. Moist, oxygen-rich
air, especially if it carries salts from ocean waters, is particularly damaging to metal components. Wind-borne sands and dusts are very
corrosive, particularly in desert regions, where sand often carries salt from ancient oceans that once covered the arid lands. Industrial air
pollution is highly corrosive. Volcanic ash is highly corrosive. The corrosion process is accelerated in hot environments.
Other substances that contribute to this corrosive mix include industrial uids and cleaning solutions, oils and fuels, battery acid, engine
exhaust particulates, and even acidic residues from leaking galleys or lavatories.
In its Technical Manual: Cleaning and Corrosion Control, the Naval Air Systems Command explains how corrosion can damage aircraft: “High
strength steels used in landing gear and launch/ recovery systems are sensitive to pitting and stress corrosion cracking, which can lead to
catastrophic failure. Aluminum alloys susceptible to exfoliation and intergranular corrosion are commonly found on wing skin and other load
carrying structures. Even magnesium, one of the most corrosion sensitive metals known, is still used in canopy frames and gear boxes. Added to
this is the ever increasing age of military aircrafts and the need to comply with stricter environmental regulations. All of these factors combine
to make corrosion prevention and control a signi cant factor in the safe and economic operation of military aircrafts.”

AGING AIRCRAFT ARE AT SPECIAL RISK

The age of the aircraft is also a signi cant factor. In recent years, progress has been made in the ght against corrosion, with the development of
better corrosion-resistant base materials, protective surface treatments, and coatings and the introduction of corrosion prevention measures
into aerospace engineering and manufacturing processes.
But older aircrafts – particularly those beyond their 20-year design life – are particularly vulnerable to corrosion, not only because they lack the
newer anti-corrosive protections, but because of their total exposure over years and decades to the harsh environments and conditions that
hasten the advance of corrosion. Even under ideal conditions, all aircrafts will experience some corrosion, but as an aircraft ages, corrosion is
more likely to develop, and to be more extensive.
About one quarter of all the commercial aircraft currently in operation are more than 20 years old, and the average age of planes in the United
States Air Force is 24 years.

THE COST OF CORROSION

Corrosion imposes a tremendous burden on aviation operations, in both direct and indirect costs.
Direct costs include:

Special cleaning and corrosion control activities

Inspection and maintenance
Repair or replacement of corroded components

Indirect costs include:

Loss of productivity due to delays, failures, etc.
Taxes and related overhead on corrosion-related maintenance and other activities
Litigation, nes, and loss of public good will after accidents and crashes

The U.S. military, which is deeply affected by corrosion in aviation operations, has made careful study of every aspect of the issue, including
costs. Among the ndings of various studies conducted by or for the U.S. military are the following:

The Department of Defense spends more than $23 billion each year to control corrosion on aircraft and other equipment in its
operations around the world. One source estimates this to be 20.5% of total maintenance costs for infrastructure, facilities, and
weaponry.
The U.S. Army’s Aviation and Missile Command spends $1.6 billion each year to address corrosion on helicopters.
Naval Air Systems Command (NAVAIR) reports that corrosion accounts for half of all aircraft depot maintenance costs.
Over FY2009-FY2013, corrosion-related costs for the U.S. Coast Guard were $344 million, or more than 22% of the Guard’s total
maintenance budget.
The House Armed Services Committee reports that about $7 billion of corrosion cost is preventable.

Corrosion also affects productivity, as demonstrated in studies done by or for the U.S. military:

In 2010-2011, the average number of days per aircraft that were unavailable due to corrosion was 15.9 days for Air Force aviation,
17.4 days for Army aviation, and 26.5 days for Navy and Marine Corps aviation.
In a similar study from FY2012, corrosion was found to be a contributing factor in 18.1% of total non-availability time for Army
aviation assets, an average of 472 hours, OR 19.7 days per year per unit.
 Naval Air Systems Command (NAVAIR) estimates for each aircraft, corrosion-related activities require 350-400 person hours of
labor (labor hours) and result in 9-10 weeks of unavailability per year.

FIRST LINE OF DEFENSE: CLEANLINESS

Aircraft designers and manufacturers have made signi cant improvements in the corrosion-resistance of modern aircraft. On the ground,
airport and military managers are paying closer attention to corrosion, and have implemented more frequent inspections and better cleaning
and maintenance.
Despite these improvements, corrosion remains a signi cant challenge for commercial and military aviation, requiring constant vigilance and
continuous preventive maintenance.
The most effective means of preventing and mitigating corrosion is to keep aircraft clean – in particular, by removing corrosive contaminants
that accumulate on the exterior of the aircraft during ight. And cleaning offers other bene ts, including:
Reducing drag and overall weight, thus improving fuel ef ciency
Facilitating inspections, done more easily on a clean aircraft
Maintaining the plane’s appearance

The frequency and intensity of cleaning operations are largely determined by the operating environment. Aircraft operated in hot, humid areas,
within ten miles of sea coasts, or in deserts, or in areas where industrial air pollution is present, or those that are not hangared, will require more
frequent cleanings than aircraft operated in dry, pollution-free environments that are protected from the elements between ights.
In its Technical Manual: Cleaning and Corrosion Control, the Naval Air Systems Command (NAVAIR) speci es these cleaning schedules for its
aircraft:

In the absence of aircraft speci c requirements, Navy aircraft shall be cleaned at least every 7 days when aboard ship and at least
every 14 days when ashore.
Under certain conditions, depending on the type of aircraft and usage, the normal wash cycle may not be suf cient. More frequent
cleaning may be required for certain types of aircraft when exposure to salt spray, salt water, or other corrosive materials occurs.
When deployed within three miles of salt water or when own below 3000 feet over salt water, daily cleaning or wipe down is
required on all exposed, unpainted surfaces, such as landing gear struts and actuating rods of hydraulic cylinders.

And for Army aircraft:

The frequency of cleaning of army aircraft shall be 30 days … unless aircraft are stationed within two miles of salt water [when
more frequent cleaning is required].
Extended or low level operations over salt water require daily fresh water rinsing.

The Air Force mandates the following intervals for thorough aircraft washing, dependent on the degree of harshness of the operating
environment:

Mild: every 180 days

Moderate: every 90 days
Severe: every 30 days
The Federal Aviation Administration suggests the following intervals:

Mild zones: every 90 days;

Moderate zones: every 45 days
Severe zones: every 15 days

The military also has requirements for aircraft cleaning for air bases in speci c geographic locations or used for certain operations:

All aircraft stationed within 1.25 miles (2 km) of salt water require a clear water rinse (CWR) at least once every 15 days unless
washed rst. All aircraft deployed to stations within 1.25 miles (2 km) of salt water for 10 days or more must follow the CWR
requirements of the deployment location.
Aircraft making two or more take-offs and or/landings, including touch-and-go landings, when the runway approach is under
3,000 feet and over salt water require a CWR after the aircraft completes the last ight of the day.
Any aircraft (primarily transient aircraft) performing only a single takeoff and/or landing requiring low-level ight (below 3,000
feet) over salt water in a single day are excluded from CWR unless there are ten or more occurrences within a 30 day period.
Search, rescue, and recovery missions or any other low-level ight operations that require aircraft to operate over salt water at
altitudes under 3,000 feet require a CWR after the aircraft completes the last ight of the day.

Cleaning, particularly for aircraft operated in harsh environments, is a lengthy, labor-intensive process. Both the military (through its branches)
and commercial aviation (through the FAA) have implemented speci c, detailed procedures for accomplishing this essential task, which is
typically carried out by specially-trained cleaning crews working by hand on each aircraft. The process requires that the aircraft be taken out of
service for many hours, sometimes for an entire day or night, depending on the type of aircraft and the harshness of the operating environment.
In addition to regular washing or cleaning, industry and military experts recommend (and often require) that aircraft operated in harsh
environments be rinsed with clear water immediately after use. While rinsing cannot replace cleaning (and does not satisfy regulatory
requirements for cleaning), it signi cantly reduces corrosion risk through the immediate removal of salts and light soils before they have a
chance to interact with aircraft surfaces and materials.
Because corrosion control and prevention activities will always be necessary and will always be a top priority, military and commercial aviation
managers constantly seek to streamline the process, reduce aircraft down time, and minimize costs.

A PRACTICAL APPROACH: AUTOMATED

FRESH-WATER RINSING
Though rinsing can be accomplished manually with hand-held hoses or other spray equipment, military regulations recommend the use of taxi-
through fresh-water rinsing facilities, by which rinsing of the entire aircraft can be accomplished more effectively and far more quickly than by
manual methods. The military further recommends that automatic, taxi-through rinse facilities, which use multiple jets to reach every part of
the aircraft exterior, including parts dif cult to reach with manual rinsing, “should be used as frequently as possible.”
Automated fresh-water rinsing facilities are a valuable supplement to cleaning operations, and offer many advantages over hand-rinsing
operations, including:
Speed – While it can take several people many hours to (RINSE) wash an aircraft, an automated rinse facility can rinse an entire
eet at under ve minutes per plane.
Effectiveness – While rinsing cannot replace washing, rinsing removes most of the salts and corrosive residues that build up
between scheduled washes, thus reducing the time and effort needed for cleaning, an essential factor in large eet operations.
Safety – During manual rinsing procedures, workers must climb on and around aircraft, carrying unwieldy equipment and hoses,
and risking slips and falls on wet surfaces. Taxi-through rinsing systems can be operated remotely, thereby reducing the risk of
worker injury.
Ef ciency – Automated rinsing facilities capture, re-cycle, lter, and re-use rinse water. This is an ef cient, cost-effective,
environmentally-friendly approach for any facility, and an especially important consideration in desert environments.

RESOURCES CONSULTED
“Aircraft Cleaning and Corrosion Control.” Chapter 6 of Aviation Maintenance Technician Handbook—General. Oklahoma City, OK: U.S.
Department of Transportation, Federal Aviation Administration, Airmen Testing Standards Branch, 2008.
https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_handbook/media/FAA-8083-30_Ch06.pdf
Aircraft Corrosion. (White Paper) NACE International (formerly National Association of Corrosion Engineers), n.d.
https://www.nace.org/uploadedFiles/Corrosion_Central/Aircraft%20Corrosion.pdf
Aircraft Corrosion. Aircraft Owners and Pilots Association, n.d.
http://www.aopa.org/Pilot-Resources/Aircraft-Ownership/Aircraft-Corrosion
Albon, Courtney. “Corrosion Exec: USAF Seeing Early CPC Progress, Cost Savings Unknown.” InsideDefense.com, July 5, 2013.
Banis, David, et al. “Design for Corrosion Control.” Aero Magazine, no. 7. Seattle, WA: Boeing Commercial Airplanes Group, 1999.
http://www.boeing.com/commercial/aeromagazine/aero_07/corrosn.html
Billion-Dollar Weather and Climate Disasters: Table of Events. National Oceanic and Atmospheric Administration, National Centers for
Environmental Information, 2015.
https://www.ncdc.noaa.gov/billions/events
Corrosion Control for Aircraft. Federal Aviation Administration Advisory Circular AC43-4A, July 25, 1991.
http://www.faa.gov/documentlibrary/media/advisory_circular/ac_43-4a_.pdf
“Corrosion Costs and Preventive Strategies in the United States.” Federal Highway Administration, NACE, and CC Technologies Laboratories,
Inc., 2002. (FHWA-RD-01-156)
https://www.nace.org/uploadedFiles/Publications/ccsupp.pdf
Hawkins, Kari. “Rinse facility designed to combat natural enemy. The Of cial Home Page of the U.S. Army, June 13, 2012
http://www.army.mil/article/81694/Rinse_facility_designed_to_combat_natural_enemy/
Herzberg, Eric F., et al. The Annual Cost of Corrosion for Coast Guard Aviation and Vessels. LMI, March, 2015.
http://www.corrconnect.org/eblast/2015_may/CoastGuardCostofCorrosion_AviationVessels_full.pdf
Herzberg, Eric. “Corrosion Of ce Updates its 2009 Report on the Cost of Corrosion Within DoD; New Report Updates Data through Fiscal
Year 2013.” CorrDefense, a publication of NACE International (formerly National Association of Corrosion Engineers), Winter 2014.
http://corrdefense.nace.org/corrdefense_Winter_2014/corrosion-of ce-updates.asp
Herzberg, Eric. “DoD Releases New Report on the Effect of Corrosion on the Cost and Availability of Army Aviation and Missile Systems.”
CorrDefense, a publication of NACE International (formerly National Association of Corrosion Engineers), November 15, 2014.
 http://corrdefense.nace.org/corrdefense_Winter_2014/aviation-missile-systems.asp
Herzberg, Eric. Impact of Corrosion on Cost and Availability to DoD. Corrosion Prevention and Control Integrated Product Team, Maintenance
Symposium, November 14, 2012.
http://www.sae.org/events/dod/presentations/2012/impact_of_corrosion_on_cost_and_availability_to_dod.pdf
“Keeping clean.” Ground Handling International, February 2015, 52-53.
http://aviator.eu/wp-content/uploads/2015/03/Aircraft-washing_Feb15_GHI.pdf
Muller, Wesley. “Keesler Technicians Solve Years-Old Mystery Illness Aboard C-130s.” Sun Herald (Biloxi, MS), April 13, s015, reprinted in
Military.com
http://www.military.com/daily-news/2015/04/13/keesler-technicians-solve-years-old-mystery-illness-aboard-c130s.html
Rose, Alan, and Keith Legg. “Predicting Corrosion in Military Aircraft. Materials Performance, February 2014.
http://corrdefense.nace.org/corrdefense_Spring2014/tech2.asp
Sisk, Richard. “F-15 Crash Raises Concerns on Aging Fleet.” DoDBuzz, September 11th, 2014.
http://www.dodbuzz.com/2014/09/11/f-15-crash-raises-concerns-on-aging- eet/
Smith, Everett J., and Scott A. Jones. “Preventing Aircraft Corrosion.” Service News (29)1: 6-16, 2005.
Lockheed Martin Corporation, Lockheed Martin Air Mobility Support https://www.lmsupport.com
http://goo.gl/E6bpJ9
Stewart, Joshua. “3-star: 20 percent of all Marine aircraft are grounded.” Marine Corps Times, March 26, 2015.
http://www.marinecorpstimes.com/story/military/tech/2015/03/26/one- fth-of-marine-aircraft-grounded/70441978/
Technical Manual: Cleaning and Corrosion Prevention and Control, Aerospace and Non-Aerospace Equipment. (F42620-00-D-0038, FA8501-
07-F-A080) This manual incorporates Interim Operational Supplement (IOS) TO 1-1-691S-1, dated 25 September 2014. Secretary of the Air
Force, 2014.
http://www.robins.af.mil/shared/media/document/AFD-091006-036.pdf
Technical Manual: Cleaning and Corrosion Control, Volume II: Aircraft. Naval Air Systems Command, April 2009, March 2010. NAVAIR 01-1A-
509-2, TM 1-1500-344-23-2.
http://goo.gl/5AZuWE

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