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Banana Skins 55

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Numbers 291 - 298 are taken from the Appendix to MIL-STD-464A dated 18 March 1997

291 From A.5.6.1 ?Non-developmental items (NDI) and commercial items?.

Several instances have been noted in ground-based applications where EMI emissions from commercial digital processing equipment have interfered with the operation of sensitive radio receivers. Of particular concern are radiated emissions from processor clock signals causing interference with communications equipment that operates from 30 to 88 MHz. Most commercial equipment is qualified by testing at a distance of three meters. The problems have been largely caused by use of the commercial items at distances of one meter or closer where the fields will be higher.

Another example is a commercial global positioning system (GPS) receiver interfering with a military GPS receiver. The out-of-band antenna emissions from the commercial receiver were picked up by the antenna of the military receiver and processed at the in-band frequency. A limited CE106 test may have identified the emission.

292 From A.5.6.2 ?Shipboard DC magnetic field environment?.

Currently there are numerous incidences of co-site, intra-ship, and inter-ship interference, as well as interference with the civilian community. For example, the Honolulu Airport air traffic control radars have been degraded by shipboard radars stationed adjacent to Pearl Harbor.

A program manager developed a system without requesting spectrum certification. After development, it was discovered that the system had the potential to interfere with other critical systems. Costly EMC testing and operational restrictions resulted, impacting the ability to meet mission requirements. Both items could have been avoided if spectrum management directives had been followed.

A base communications officer funded the purchase of commercially approved equipment. The user was unable to get a frequency assignment because the equipment functioned in a frequency range authorized? for only non-government operation. A second system had to be purchased to satisfy mission requirements.

293 From A.5.7 ?Electrostatic charge control?. A maintenance person was working inside a fuel tank and experienced an arc from his wrench when removing bolts. It was found that maintenance personnel were routinely taking foam mats into the tank to lie on while performing maintenance. Friction between the mat and clothing allowed a charge buildup which caused the arc. All static generating materials should be prohibited from the tank during maintenance.

Many equipment failures have been attributed to ESD damage of electronic parts.

From A.5.7.1 ?Vertical lift and in-flight refueling?.

To protect personnel on the ground from receiving electrical shocks, it is standard practice for rotorcraft to touch the ground with the hook before it is connected to the cargo. As the cargo is lifted, the whole system (aircraft and cargo) will become recharged. Again, when the cargo is lowered to the ground, it must touch the ground to be discharged before handling by personnel. The aircraft system and cargo often see several electrical discharges as the vertical lift process is executed.

During in-flight refueling, pilots have reported seeing arcing between the refueling probe and the fueling basket during mating. These discharges were several inches long. Based on these observations, the 300 kV number was derived. Aircraft that have experienced discharges from inflight refueling have had upsets to the navigation system resulting in control problems.

295 From A.5.7.2 ?Precipitation static (P-static)?.

A.5.7.2 A fighter aircraft was experiencing severe degradation of the UHF receiver when flying in or near clouds. Investigation revealed that the aircraft was not equipped with precipitation static dischargers. Installation of these devices solved the problem.

An aircraft had a small section of the external structure made of fiberglass. Post-flight inspections required personnel to get in close proximity to this non-conductive structural component. On several occasions, personnel received significant electrical shocks which caused them to fall from ladders and be injured. Corrective action was easily accomplished be applying a conductive paint to the surfaces exposed to airflow and personnel contact.

Static discharges from the canopy were shocking pilots on a fighter aircraft during flight. Charges accumulating on the outside of the canopy apparently migrated slowly through the dielectric material and discharged to the pilot?s helmet when sufficient charge appeared on the inside surface. A grounded conductive finish on the inside of the canopy fixed the problem. Experience with an ungrounded conductive finish aggravated the problem.

When an aircraft was flying in clouds during a thunderstorm, the pilot was unable to transmit or receive on the communications radio. Further investigations were performed with the most reasonable conclusion that the radio blanking was caused by electrostatic discharge. Several incidents were also reported where pilots and ground crews received shocks due to static discharges from aircraft canopies. These incidents occurred on the carrier deck after the aircraft had been airborne for several hours.

It was discovered on an aircraft that was experiencing p-static problems that the static dischargers had been installed using an adhesive that was not electrically conductive.

Coordination between structural and electrical engineer personnel is necessary to ensure that all required areas are reviewed. For example, a structural component on an aircraft was changed from aluminum to fiberglass and experienced electrostatic charge buildup in flight which resulted in electrical shock to ground personnel. The structural engineer made this change without proper coordination, which resulted in an expensive modification to correct the shock problem.

296 From A.5.7.3 ?Ordnance subsystems?.

Explosive subsystems have been initiated by ESD caused from human contact or other sources of ESD.

297 From A.5.8.3 ?Hazards of electromagnetic radiation to ordnance (HERO)?.

Several incidences onboard Navy ships involving the inadvertent firing of rockets and missiles have resulted in catastrophic loss of life and equipment. There have been numerous explosive mishap reports involving RF induced, uncommanded actuation of automatic inflators worn by aircrew personnel both on flight decks and in-flight while launching from and landing on the carrier. These problems pose a tremendous hazard to aircrews, especially those in-flight at the time of occurrence.

>strong>298 From A.5.11.1 ?Aircraft grounding jacks?.

Aircraft fuel fires have been attributed to electrostatic discharge. Precisely demonstrating that an electrostatic discharge caused a mishap is usually not possible due to difficulty in reproducing conditions that were present.

Grounding jacks on aircraft in the field have been found to be electrically open-circuited with respect to the aircraft structure due to corrosion. It is important that corrosion control measures be implemented at the time of installation. (MIL-STD-464A is entitled ?Department of Defense - Interface Standard -Electromagnetic Environmental Effects - Requirements for Systems ?. To obtain a free copy, type MIL-STD-464 into the Google search engine at com, and it will quickly find sites from where it can be downloaded.)

299 The latest Patriot scandal concerns the deaths of the crew of Yahoo 76, a British Tornado GR-4 that was shot down by a Patriot air and missile defences unit over Kuwait on 22 March last year as it descended with another Tornado in a pre-planned ?safe? corridor towards its home base west of Kuwait City.

What the data shows is that the Patriot did not initially identify the Tornado as a target at all, and that the ?missile? it registered was in fact a ?ghost? ? an illusion probably generated by electronic interference from other nearby Patriot units. Furthermore, the Patriot detected this false target 15 kilometres east of the approaching Tornados, heading not towards the Patriot but towards a troop encampment roughly 15 kilometres to the north. If it had been heading towards the Patriot, the battery?s weapon control computer would have classified it as an Air Threat Category 1. Instead, it classified it as a Category 9, a threat level so low that the computer did not even mark it for engagement.

The Patriot?s crew, believing they were under attack, launched an Interceptor missile at the false target, which by this stage had ?moved? into the vicinity of the Tornados. In the absence of any other target, the interceptor?s radar homed in on one of the planes. (Taken from: ?Unfriendly Fire?, by Theodore Postol, Professor of Science, Technology and National Security Policy at the Massachusetts Institute of Technology, New Scientist, 2 October 2004, page 23.)

300 As usual, we celebrate another hundred Banana Skins with something a little more unusual, tongue-in-cheek, or just plain funny. Make up your own mind about which category this one falls into.

Reports of anomalous aerial objects (AAO) (UFOs to the rest of us ? Ed.) appearing in the atmosphere continue to be made by pilots of almost every airline and air force of the world in addition to private and experimental test pilots. This paper presents a review of 56 reports of AAO in which electromagnetic effects (E-M) take place on-board the aircraft when the phenomenon is located nearby but not before it appeared or after it had departed. These effects are not related to the altitude or airspeed of the aircraft. The average duration of these sightings was 17.5 minutes in the 37 cases in which duration was noted. There were between one and 40 eye witnesses (average = 2.71) on the aircraft. Reported E-M effects included radio interference or total failure, radar contact with and without simultaneous visual contact, magnetic and/or gyro-compass deviations, automatic direction finder failure or interference, engine stopping or interruption, dimming cabin lights, transponder failure, and military aircraft weapon system failure. There appears to be a reduction of the E-M energy effect with the square of increasing distance to the AAO. These events and their relationships are discussed. This area of research should be concentrated on by other investigators because of the wealth of information it yields and the physical nature of AAO including wavelength/frequency and power density emissions. (Taken from the Abstract for ?Fifty-six Aircraft Pilot Sightings Involving Electromagnetic Effects?, Richard F. Haines, Ph.D, Copyright 1992,, 16 Jun 03)

301 EMI hardness evaluations under the Navy?s Air Systems? EMI Corrective Action Program (AEMICAP) have shown that the hardness of aircraft is degraded over time. Electrical inspections have shown numerous instances of foreign object damage, excessive chaffing of wires, and improper splicing and terminations. Bonding measurements performed over a ten year period on a Navy fighter aircraft indicates 10-15% out of specification conditions on a new aircraft, 40-60% out of specification conditions on a five year old aircraft and 70-80% out of specification conditions on a ten year old aircraft. These out of specification bonding conditions result in inadequate termination of shields and boxes and degrade shielding effectiveness. During EMC tests, the effects of corrosion and maintenance practices on the EMC design have been noted. For example, composite connectors were incorporated in the pylons of a Navy attack aircraft to correct a severe corrosion problem on the existing aluminum connectors. The composite connectors are more resistant to the corrosion than aluminum. They do, however, oxidize and produce a powdery residue on the connector. The maintenance personnel would then wire brush this residue, thereby eliminating the outer conductive coating, severely degrading the connector conductivity, and introducing potentially more severe corrosion problems. (Taken from MIL-STD-464A, Appendix A.5.9 ?Life cycle, E3 hardness?. ?HERO? stands for Hazards of Electromagnetic Radiation to Ordnance.)

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