Alitalia Flight 404
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Alitalia Flight 404 (AZ404/AZA404) was an international passenger flight scheduled to fly from
Linate Airport Milan Linate Airport is the third international airport of Milan, the second-largest city and largest urban area of Italy, behind Malpensa Airport and Orio al Serio Airport. It served 9,233,475 passengers in 2018, being the fifth busiest air ...
in
Milan Milan ( , , Lombard: ; it, Milano ) is a city in northern Italy, capital of Lombardy, and the second-most populous city proper in Italy after Rome. The city proper has a population of about 1.4 million, while its metropolitan city h ...
,
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
, to
Zürich Airport Zürich Airport (), french: Aéroport de Zurich, it, Aeroporto di Zurigo, rm, Eroport da Turitg is the largest international airport of Switzerland and the principal hub of Swiss International Air Lines. It serves Zürich, Switzerland's larg ...
in
Zürich Zürich () is the list of cities in Switzerland, largest city in Switzerland and the capital of the canton of Zürich. It is located in north-central Switzerland, at the northwestern tip of Lake Zürich. As of January 2020, the municipality has 43 ...
, Switzerland, which crashed on 14 November 1990. The
Douglas DC-9-32 The McDonnell Douglas DC-9 is an American five-abreast single-aisle aircraft designed by the Douglas Aircraft Company. It was initially produced by the developer company as the Douglas DC-9 until August 1967 and then by McDonnell Douglas. After ...
, operated by
Alitalia Alitalia - Società Aerea Italiana Società per azioni, S.p.A., operating as Alitalia (), was an Italian airline which was once the flag carrier and largest airline of Italy. The company had its head office in Fiumicino, Metropolitan City of ...
, crashed into the woodlands of
Weiach Weiach is a municipality in the district of Dielsdorf in the canton of Zürich in Switzerland. History Weiach is first mentioned in 1271. It has belonged to Swiss Confederation since 1424. Since 1962 there has been a gravel industry located i ...
as it approached Zurich Airport, killing all 46 people on board. A Swiss investigation concluded that the crash was caused by a
short circuit A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit ...
, which led to the failure of the aircraft's NAV receiver. The malfunction went unnoticed by the crew, who likely believed they were on the correct flight path until the crash. Swiss authorities also blamed inadequate
crew resource management Crew resource management or cockpit resource management (CRM)Diehl, Alan (2013) "Air Safety Investigators: Using Science to Save Lives-One Crash at a Time." Xlibris Corporation. . http://www.prweb.com/releases/DrAlanDiehl/AirSafetyInvestigators/ ...
, exemplified when the captain vetoed the first officer's attempted
go-around In aviation, a go-around is an aborted landing of an aircraft that is on final approach or has already touched down. A go-around can either be initiated by the pilot flying or requested by air traffic control for various reasons, such as an unstab ...
, along with the absence of lighting on Stadlerberg Mountain and a known problem with errors in reading the drum pointer altimeter of the aircraft. The final report by the Federal Aircraft Accidents Inquiry Board requested several major changes and made further recommendations.


Accident

During the approach to runway 14 of Zürich International Airport, the pilot's
instrument landing system In aviation, the instrument landing system (ILS) is a precision radio navigation system that provides short-range guidance to aircraft to allow them to approach a runway at night or in bad weather. In its original form, it allows an aircraft to ...
(ILS) display gave incorrect values due to a faulty receiver. It falsely indicated that the aircraft was about 1,000 feet higher than it actually was, which also prevented the Ground proximity warning system (GPWS) from reading the situation and sounding a warning. The ILS receiver of the first officer was working correctly and displayed the dangerously low approach. Without thoroughly examining which value was correct, the pilot decided to ignore the second device, aborting a
go-around In aviation, a go-around is an aborted landing of an aircraft that is on final approach or has already touched down. A go-around can either be initiated by the pilot flying or requested by air traffic control for various reasons, such as an unstab ...
maneuver initiated by the first officer. Shortly afterward, at 20:11 CET, the plane struck Stadlerberg Mountain at , killing all 40 passengers and six crew. The aircraft's first impact was with trees on the right side of the aircraft, causing several essential parts on the right side of the aircraft, such as the right-wing flaps and the outer right wing, to detach. As a result, the aircraft produced an asymmetric lift force and began to roll to the right, finally slamming into the mountain in a nearly inverted position. Firefighters and police were immediately dispatched to the crash site but the fire was so intense that it took an entire day to put out. Eyewitnesses stated that "the plane was burning like a volcano." Linate Airport immediately set up a crisis center to handle the relatives of the victims aboard the flight.


Aircraft

The aircraft involved in the crash was a Douglas DC-9-32, built-in 1974 with serial number 47641 and the registration number I-ATJA. The aircraft was first delivered to
Aero Trasporti Italiani Aero Trasporti Italiani S.p.A (ATI) was an Italian airline headquartered in Naples, Italy. It was founded on 16 December 1963 as a subsidiary of Alitalia to take over secondary domestic routes in southern Italy operated by another Alitalia subsid ...
, a subsidiary of
Alitalia Alitalia - Società Aerea Italiana Società per azioni, S.p.A., operating as Alitalia (), was an Italian airline which was once the flag carrier and largest airline of Italy. The company had its head office in Fiumicino, Metropolitan City of ...
and was transferred to Alitalia in October 1988. According to investigators, the aircraft had accumulated more than 43,400 cycles and also stated that the aircraft had been inspected 10 days prior to the accident.


Passengers and crews

The aircraft was carrying 40 passengers and 6 crew members. The crew members consisted of two pilots and four flight attendants, all of whom were Italian citizens. Two Japanese officials from the
Oki Electric Industry , commonly referred to as OKI, OKI Electric or the OKI Group, is a Japanese information and communications technology company, headquartered in Toranomon, Minato-ku, Tokyo and operating in over 120 countries around the world. OKI produced the fi ...
were also on board and many other passengers were laborers heading home after working in Milan's industrial area. Among the passengers on board was Italian actor . The captain was Raffaele Liberti, aged 47, a 20-year veteran of Alitalia with a total flying time of more than 10,000 hours. The first officer (the pilot flying) was Massimo De Fraia, aged 28, who had joined Alitalia in 1989 and was much less experienced than captain Liberti.


Investigation

Swiss investigators were informed about the accident one hour after the crash. The investigation involved at least 80 Swiss investigators. Additionally, Italian Interior Minister
Vincenzo Scotti Vincenzo Scotti (born 16 September 1933) is an Italian politician and member of Christian Democracy (Italy), Christian Democracy (DC). He was Italian Minister of the Interior, Minister of the Interior and Italian Minister of Foreign Affairs, Mini ...
sent a team of investigators to the crash site along with the United States'
NTSB The National Transportation Safety Board (NTSB) is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incid ...
and
FAA The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
. Both the Flight Data Recorder and the Cockpit Voice Recorder were recovered from the crash site. In the initial hours after the accident, several witnesses claimed that the aircraft was on fire before it hit Stadlerberg while others claimed that the aircraft had exploded before it impacted terrain. Josef Meier, a spokesman for Swiss air traffic control authorities stated in a news conference that all possible causes, including terrorism, were being evaluated by the investigators. Italian news media reported that the mountain was covered with cloud and that there was heavy rain in the area, while Swiss investigators claimed that visibility was good during the accident with light showers occurring at the airport. On 16 November, an official from Swiss investigation team stated that the aircraft was flying at a lower altitude than it should have been: "The plane was too low on its approach, and was slightly off course. he captainwas not following the radio beacon signals." The statement did not say why the plane was too low.


Pilot error

The first officer had initiated a go-around but the captain aborted it. He said, "Hold the glide slope, can you hold it?". The first officer replied, "Yes". Investigators working with McDonnell Douglas concluded that, if the captain had not interrupted the go-around and had a situation awareness as the first officer had, the disaster would have been averted. Investigators believe that the reason for the bad call was that the captain had no situation awareness at all and was completely dissatisfied with the first officer's performance during the flight. As a result, the captain showed a lack of trust in his first officer.


Stadlerberg Mountain

As Stadlerberg Mountain is relatively far from the runway, per
International Civil Aviation Organization The International Civil Aviation Organization (ICAO, ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international sc ...
(ICAO) standards, obstruction lighting was not required. The mountain could not be seen during the night, and thus could endanger flights. This problem had been discussed between
Swissair Swissair AG/ S.A. (German: Schweizerische Luftverkehr-AG; French: S.A. Suisse pour la Navigation Aérienne) was the national airline of Switzerland between its founding in 1931 and bankruptcy in 2002. It was formed from a merger between Bal ...
, Swiss airport authorities, and the Swiss
Federal Office of Civil Aviation The Federal Office of Civil Aviation (FOCA, german: Bundesamt für Zivilluftfahrt; french: Office fédéral de l'aviation civile; it, Ufficio federale dell'aviazione civile) is the Swiss civil aviation agency, a division of the Federal Departm ...
(FOCA) since 1976. Analysis of the cockpit voice recorder did not give any indications that the crew was looking for the cloud-capped mountain during the approach.


NAV Receiver failure

Recordings from the black boxes showed that the navigation instrument, the ADI/HSI, had apparently captured the glideslope. At the time when the glide slope was captured, the aircraft was flying about 1,300 feet below the glide path. Examining the receiver with a microscope, the investigation revealed that during the impact, the glide path indicator had been positioned just above the center "on glide" position, which means that the glide path had been captured. Investigators also revealed that all NAV instruments were following the glide path, although the aircraft was flying below the nominal glide path. At the time, investigators didn't find any defects on the instrument. Detailed examination of the NAV showed that the NAV mode, during its operation in-flight, can lead to a completely false
LOC LOC, L.O.C., Loc, LoC, or locs may refer to: Places * Lóc, a village in Sângeorgiu de Pădure, Mureș County, Romania * Lócs, a village in Vas county, Hungary * Line of Contact, meeting place of Western and Eastern Allied forces at the e ...
(horizontal alignment) or GS (vertical alignment) indication ("ON" indication). A small red flag should have appeared on the indicator when the error occurred, but it did not. McDonnell Douglas provided the investigators a letter, which it had sent six years earlier (24 August 1984) to every operator of DC-8, DC-9, C-9, and MD-80 aircraft equipped with the faulty NAV receiver, which related to the NAV switching failure mode. McDonnell Douglas had held a seminar about the faulty NAV in 1985 in Long Beach, California and Alitalia had sent three pilots there. However, the message from both the letter and the seminar was not transmitted to Alitalia operating crews. They, including the crew of Flight 404, were unaware of the possible false indication.


Cause of NAV Receiver failure

According to McDonnell Douglas, a short circuit or an open circuit in certain models of radio navigation (
VOR VOR or vor may refer to: Organizations * Vale of Rheidol Railway in Wales * Voice of Russia, a radio broadcaster * Volvo Ocean Race, a yacht race Science, technology and medicine * VHF omnidirectional range, a radio navigation aid used in a ...
/ ILS) receivers could cause navigation instruments to indicate "zero deviation". Thus, raw data deviation information on the attitude direction indicator, displayed by the flight director bars, and the horizontal situation indicator could center and remain centered with no failure or warning flag in view. Not only did it fail to warn the pilots about the problem, but this open circuit also prevented the autopilot and the Ground proximity warning system (GPWS) from receiving the proper course and glide path deviation signals, resulting in neither instrument warning about the imminent danger. The autopilot continued to guide the aircraft according to the previously established crew inputs and the GPWS did not sound an alarm since the crew believed that they were on the correct glide path, while in reality, they were not. As a crosscheck of the system, the captain and the first officer would normally use two separate VOR/LOC receivers for navigation information. However, due to the absence of a warning flag, the captain and the first officer believed that they were on the right track, and later used the NAV switching function to select the malfunctioning VOR/LOC receiver on both panels.


Altimeter misreading

The aircraft was equipped with an older "drum pointer" altimeter. This type of altimeter has several disadvantages; for instance, in certain pointer positions, the needles partially obscure the readout resulting in the inability to accurately determine altitude. The
United States Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signal ...
had noted this altimeter design as problematic in several training and safety reports. In the previous year, there were several accidents that were caused due to altimeter misreading.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
research showed that, from a survey of 169 US pilots, 137 pilots said that they had already misread an altimeter at least once, 134 pilots had observed another pilot misreading an altimeter, 85% of the pilots explained that they had noticed that misreading has occurred more than once in the cockpit during their work, and most of the misreading occurred during the approach phase. The survey then concluded several things, based on the comments from the pilots: * "This altimeter takes more concentration than should be necessary to read accurately." * "The small drum window is a complication in the instrument and squite small, often requiring a 'double look' and diverting attention from the needle." * "Misreads always occur at a lower altitude when pilots split attention between more activities." * "The most stressful situations produced more misreads." * "A quick look after eing distractedcan induce a reading of 1,000 feet off if the barrel drum is halfway between thousands." Investigators stated that the crew of Flight 404 might have misread the altimeter. It is plausible that the captain had misread the altimeter, believing that the outer marker height of 2,650 feet had only been undershot by a small amount. He then countermanded the co-pilot's order for a go-around, as he thought that he could attain the correct glide path within a short time with a reduced rate of descent.


Aftermath

Reviewing the chain of events, the investigation board made several recommendations in order to avoid similar scenarios. Improved rules for communication among pilot and co-pilot during landing have been implemented, and possibilities of misreading flight altimeters have been pointed out to pilots. Most importantly, new rules prohibit the aborting of a go-around once it has been initiated, regardless of the rank and function of the crew member initiating the go-around. Proper review of decisions and clear communications are part of
crew resource management Crew resource management or cockpit resource management (CRM)Diehl, Alan (2013) "Air Safety Investigators: Using Science to Save Lives-One Crash at a Time." Xlibris Corporation. . http://www.prweb.com/releases/DrAlanDiehl/AirSafetyInvestigators/ ...
. Several major changes were made after the accident: * Alitalia added the NAV receiver failure problem to their training and also added the actions that the crew should take in case it happens. * Alitalia forbade interrupting a go-around. Once called, the go-around procedure has to be done. This rule is now general in almost all airlines. * Swiss aviation authorities added lights to Stadlerberg Mountain. * McDonnell Douglas revised their training manual to add information about the possibility of NAV failure. Additionally, several recommendations were made: * NAV equipment without monitoring of the output signal should no longer be used. * The drum pointer altimeter should no longer be used. Authorities asked that this recommendation be implemented with immediate effect. * The GPWS should operate even in the case of NAV failure. Alitalia continued to utilize the callsign of the accident aircraft ("Alitalia 404") after the crash. It was primarily used, until Alitalia ceased operations, on a Rome–Frankfurt route.


References


External links


Final report on the accident by the official commissionArchive
- Federal Aircraft Accidents Inquiry Board *
Final report on the accident by the official commissionArchive
- Federal Aircraft Accidents Inquiry Board - Original version in German: Pages 53–57/57 (PDF Document pp. 53–57 of 154) are a summary in French
ASN Aircraft accident McDonnell Douglas DC-9-32 I-ATJA Stadlerberg
* {{Portal bar, Aviation, Italy, Switzerland, 1990s Accidents and incidents involving the McDonnell Douglas DC-9 404 Aviation accidents and incidents in 1990 Aviation accidents and incidents in Switzerland 1990 in Switzerland November 1990 events in Europe Airliner accidents and incidents involving controlled flight into terrain Airliner accidents and incidents caused by instrument failure Airliner accidents and incidents caused by pilot error