FSI Flight SafetySECOND QUARTER Information 2004 SECOND QUARTER 2004 Sound Spectrum Analysis Enhanced Vision Systems Communications System Safety Accidents / Incidents FSI CONTENTS To FSI Subscribers: Welcome to the sixth issue of Flight Safety Information Quarterly Journal. The jour- nal is produced in order to create safety awareness, pro- vide timely and valuable safety information, and to ulti- mately prevent accidents. I welcome contributing input, articles, and photos from the readers. Curt Lewis, P.E., CSP Published by www.fsinfo.org 3 Sound Spectrum Analysis Managing Editor Curt Lewis P.E., CSP 7 Enhanced Vision Systems [email protected] Associate Editors Erica Lush 9 Communications [email protected] Erdem Serifoglu [email protected] 13 System Safety Webmaster Randy Enberg 16 Accidents / Incidents Overview [email protected] 2 FSI Sound Spectrum Analysis (Another Investigative Technique) American Airlines Flight 587 What if we could detect the cause of aircraft How are CVR recordings analyzed? The an- damage simply by listening to the sounds re- swer: sound spectrum analysis. Sound spec- corded in the cockpit? Detecting damage to air- trum analysis is a technique that compares the craft after an accident or incident is conducted amplitudes of sounds, and plots the distribution with the help of various tools and analysis tech- on a three-dimensional graph. This type of niques. Cockpit Voice Recorder (CVR) data is a analysis depicts changes or modulations in useful tool that investigators use to obtain audio sounds, and it can pinpoint the time when these information from the cockpit during the se- changes occur. quence of flight. There are two types of sound Sound spectrum analysis can be used for analyz- that may be analyzed, speech and non-speech ing both speech and non-speech audio informa- audio information. tion. Believe it or not, non-speech sounds are The CVR records audio information on 4 chan- highly important to the investigation of aircraft nels. Non-speech information is recorded on damage because the background cockpit sounds channel 1 from the Cockpit Area Microphone can reveal problem areas of the aircraft during (CAM). The CAM records thumps, clicks and the time leading up to the accident. other sounds occurring in the cockpit other than Non-speech data from the CAM can be analyzed speech. Channels 2 and 3 of the CVR record with sound spectrum analysis to detect whirl speech audio information from the Captain and flutter, as well as possibly differentiating a bomb First Officer’s audio selector panels. Channel 4 explosion from cabin decompression. Spectrum records the audio information from the jump analysis can also be used to confirm that the seat/observer’s radio panel. clicks and thumps recorded by the 3 FSI Sound spectrum analysis is performed with the CAM are simply cockpit controls, and the sound aid of a personal computer and specialized spec- of the aircraft moving through the air. tral analysis software. The audio information recorded from the CVR is loaded to the software program, which displays the information in a graphical representation. Each channel from the CVR can be separated to analyze each section of audio information if necessary. Pan Am Flight 103 disintegrated over Lockerbie, Scotland in 1989 due to a bomb explosion. Speech information recorded by the CVR can be analyzed with spectrum analysis in order to match the recorded voices to the appropriate per- Spectrographs can display data in color and in son. To further understand sound spectrum analysis, As previously mentioned aircraft damage can you must first understand the physics of sound. be assessed effectively with the use of a sound spectrum analysis. The National Transporta- Sound is the vibration of any substance. Sound tion Safety Board (NTSB)’s Sound Spectrum is processed in the form of waves. A wave is a Group has assisted with many major accident disturbance that travels through a medium. The investigations by analyzing the sounds ob- most common medium that sound waves travel tained from the CVR and CAM. Such acci- through is air, but it may also travel through sub- dents that the sound spectrum group have stances such as water, metal, or wood. The am- worked on include American Airlines, Flight plitude of a sound is the height of the wave. 587, in Belle Harbor, New York, and Egypt Loud sounds will have higher waves than softer Air, Flight 990, off the coast of Nantucket, waves, resulting in higher amplitude. Sounds are Massachusetts. generally measured in cycles, or frequencies. American Airlines Flight 587 Sound may be represented graphically as a waveform, spectral plot, sonogram, or spectro- American Airlines, Flight 587, crashed shortly graph (spectrogram). Spectrographs are the after take off from John F. Kennedy Interna- graphical representations used commonly in tional Airport on November 12, 2001. The air- sound spectrum analysis be cause it presents craft encountered wake turbulence forces from sounds in a three-dimensional form and it shows the aircraft that departed just before flight 587, a clearer visual of how the amplitudes of various and the vertical tail of the aircraft separated components of a sound change. from it and landed over two miles from the main site of impact. 4 FSI The NTSB’s Sound Spectrum Group examined Egypt Air Flight 990 the CVR to document any signals of airframe During the investigation of Egypt Air, Flight vibration or flutter. In order to examine this, the 990, the sound spectrum group examined the au- team had to analyze the sound of the aircraft dio information from the CVR to identify un- while it moved through the air. The airframe known sounds or electrical disturbances. The will vibrate at a resonant frequency during nor- team also needed to determine the pilot who mal flight. An airframe vibration of the aircraft spoke the phrases during the last several minutes might change the constant vibration or change of the recording, and identify who was in the the normal steady background noise recorded on cockpit during the last few minutes of the re- the CVR. The team found that the vibration of cording. The team did not identify any unusual the aircraft remained relatively constant, and the sounds in the cockpit or from the aircraft, but only change in vibration occurred during the re- they were successful in identifying the pilot who traction of the landing gear, flaps, and slats. spoke the final phrases recorded, and they identi- fied the individuals in the cockpit during the last minutes of flight. Landing in LAX earlier during the day of the ac- cident. An engine from Flight 587. In order to examine the phrases spoken, the Another technique was used to examine airframe sound spectrum group used an analysis tech- vibration, which involved a low pass filter ap- nique called voice print methodology. This plied to the CVR recording. A signal processor type of analysis involves comparing the uniden- calculated the frequency content of the low pass tified spoken phrases with known speech sounds. signal that was passed through it. Neither of the two methods identified airframe vibrations or The individual phrases of speech were first bro- flutter associated with flight 587. ken down and the frequency spectrum of each The final examination by the Sound Spectrum phrase was plotted. The plots of the frequency Group was to document unknown or unusual spectrum for each phrase were compared with sounds in the cockpit or from the aircraft. There other known speech samples. The team was able were many sounds recorded including thumps, to identify the pilot who spoke the phrases be- clicks, squeaks, rattles, etc. These sounds were cause every person has their own unique har- later identified as the movements of items in the monic variations when they speak. A funda- cockpit during the wake turbulence. The team mental (primary) frequency is produced when did not identify any sounds that could be associ- the vocal cords vibrate. Harmonics are over- ated with the tail separation of the aircraft. tones of the fundamental frequency. 5 FSI From this analysis of plotting frequencies and harmonics, the team was able to identify the First Officer as the speaker during the last several minutes of the recording. The sound spectrum group used the plots of the voice print study to determine who was in the cockpit at the end of the recording. After the sound of the cockpit door opening was recorded, the team was able to identify that the door never re-opened, and that the Captain and First Officer were both in the cockpit. Conclusion Sound Spectrum Analysis has recently been a successful tool to help in the investigations of aircraft accidents. Each recorded sound from the CVR acts as a signature, which can be compared and identified by plotting the sounds in a spec- trograph. The research of sound spectrum analy- sis is fairly new to the accident investigation process. If we knew more about the possibilities of the damage it could detect, then the effects of aircraft damage, such as the disintegration of TWA Flight 800, could be explained more effec- tively. The cause of TWA 800’s disintegration is still unknown today. 6 FSI Enhanced Vision System is no longer a futuristic dream. EVS is a developing safety tool which has the potential of becoming a turning point for aviation safety. proach and landing are to Evolving technologies there is a need for new be done at an airfield dur- used in the aviation in- technologies to prevent ing night time and/or poor dustry are successfully catastrophic runway and visibility. enabling development of taxiway incursions, es- new software and hard- pecially during the times Enhanced vision system is ware which have signifi- of reduced visibility.