Diversion
Diversion
Definition
DIVERSION (DVRSN)- Flights that are required to land at other than their original destination for reasons beyond the control of the pilot/company, e.g. periods of significant weather.
Source: US FAA JO 7110.65
Description
A diversion is a situation where the pilot decides to land the aircraft at a different aerodrome than originally planned. Diversions can be divided into three broad groups:
- Air turnbacks. These are situations where the aircraft returns to the departure aerodrome.
- En-route diversions. These are situations where the aircraft diverts to an alternate before reaching the vicinity of the planned destination aerodrome.
- Destination diversions. These are situations where the aircraft diverts to an alternate after reaching the vicinity of the planned aerodrome.
Diversions can happen for a number of reasons, e.g.:
- Adverse weather, e.g.
- thunderstorms (either at destination or en-route leading to excessive extention of the route)
- heavy rain/flooded runway at destination
- significant crosswind at destination
- Aerodrome closure due to e.g.
- maintenance works
- the flight arriving outside opeating hours (too early or too late)
- Emergency or abnormal situation at the destination, e.g.
- security issues
- accident with another aircraft leading to runway/aerodrome closure
- Emergency or abnormal situation on board, e.g.:
- System or component failure (e.g. engine, electrical, pressurization, hydraulic, etc.)
- Insufficient fuel
- Medical issues (affecting either a passenger or a crew member)
- Unruly passenger(s)
- Bomb threat/hijack
- Clearance issues. Examples of these include:
- the aircraft is not allowed to land at the destination aerodrome
- some en-route airspace that either prevents the aircraft from reaching its destination or circumventing it extends the flight route to the point where fuel is no longer sufficient to reach the destination.
- Military interception
Excluding some security-related situations (hijack/interception), the decision to divert is made by the pilot in command. In most cases the new destination is (one of) the alternate(s) specified in the flight plan but depending on the circumstances (e.g. if they are all unreachable or considered inappropriate) other suitable alternatives can be used. Before making the final decision the pilot usually gathers additional information by e.g. the operator or the ATS unit they are in contact with. The latter can provide valuable information and assistance such as:
- weather (current and forecast) at the alternate(s) or other suitable aerodromes
- providing additional options (aerodromes not included as alterantes in the flight plan but probably suitable for the particular situation).
- navigation assistance (e.g. headings or direct routing to appropriate waypoints), especially in case the diversion is to an aerodrome that has not been planned for.
- runway and navaid information (e.g. runway length, available approach types, etc.).
- forwarding information to other ATS units along the modified route as well as the destination aerodrome and coordination of entry and landing permissions.
A&I Examples
Air Turnback
On 17 October 2023 a Boeing 737-800 passing FL130 after departing Manchester received a cabin pressurisation warning, and the crew recognised that both engine air bleeds were off. After correcting this, climb was continued without donning oxygen masks until an air conditioning pack fault occurred, which prompted the operator to request a return which was uneventful. The bleeds-off condition had arisen after maintenance and had then not been recognised at release to service or during crew preflight checks.
On 19 October 2022, an Embraer E175-200 had just departed Dublin when the first officer, who was acting as Pilot Flying, became incapacitated. The captain immediately took over all flying duties, requested assistance for the first officer from the cabin crew, and declared a MAYDAY. The aircraft then returned to land without further significant event although a bird strike occurred on approach. The 35-year-old first officer was medically assessed, and the conclusion was that he had “low blood pressure (and) a possible lack of water and food” which would have been exacerbated by the rising cabin altitude after departure.
On 20 February 2023, a Fokker 70 flight crew realised, late into descent, that the landing altitude for their destination, Port Moresby, had not been set. With insufficient time to eliminate the cabin pressure differential automatically, they attempted to use manual control. When it became clear this had not worked, a go-around was initiated. When the cabin pressure differential then rose rapidly to 6 psi, multiple passenger ear/nose/throat injuries resulted, some serious. Another abnormal procedure was then actioned, and this resolved the situation and the aircraft was able to land.
On 20 December 2012, a PW4168A-engined Airbus A330-200 was climbing through FL220 after departing Phuket, Thailand, at night when sudden uncontained left engine failure occurred. Engine shutdown and initiation of a return was followed by loss of the green and then blue hydraulic systems. Shortly after this, a relatively uneventful landing followed with only minor damage but “without pilot assessment or knowledge of the safety margin." As the findings of the investigation raised still-relevant concerns about the way this multiple-failure scenario was handled, it was felt useful to publish the 148-page final report eleven years later.
On 4 October 2023, an Airbus A321 climbing out of London Stansted with the 18 occupants all seated towards the front of the passenger cabin was discovered to have several missing or damaged windowpanes on the left side towards the rear. The aircraft returned to land where damage was also found to one of the horizontal stabilisers. The window panes fell out because of damage by infrared energy emitted from high-intensity lights during a filming event the previous day. Four previous similar events were identified but it was found that knowledge of them was not widespread in the aviation community.
En-route diversion
On 22 January 2022, an Airbus A320 departing the uncontrolled airport at Hayden announced its intended runway 10 takeoff after failing to hear calls from a Beech King Air 350 that it was inbound to reciprocal runway 28. When the A320 subsequently announced they were commencing takeoff from 10, the King Air Pilot responded by asking if the A320 was intending a quick turn-out. Almost immediately after confirmation, the A320 Captain rotated 24 knots before the correct speed with a consequential tailstrike. Once airborne, an evasive right turn was commenced with the reciprocal-direction King Air just over 2 nm away.
On 29 November 2021, the crew of a Bombardier CRJ900 (C-GJZV) which had just taken off from San Diego at night were presented with a fuel imbalance indication. The imbalance slowly increased until, once level at FL340, a further annunciation indicated that the maximum permitted imbalance had been reached. Actioning the corresponding checklist did not resolve the problem, so procedurally recommended shutdown of the low fuel side engine was performed, followed by a MAYDAY diversion to Los Angeles. The imbalance was attributed to inadvertent crew selection of ‘gravity crossflow’ prior to takeoff instead of the immediately adjacent ‘crossflow auto override.'
On 10 February 2023, a Boeing 767-300ER had problems setting climb thrust after takeoff from Edinburgh, and a right engine control fault was annunciated. It was decided that the intended transatlantic flight should divert to Prestwick. Right engine vibration became apparent and the engine was set to idle, and it shut down after landing. On arrival at the assigned parking position, fuel was seen leaking from the right wing, and a rapid passenger disembarkation was completed. Vibration due to engine imbalance after turbine blade fracture was found to have caused the fuel leak.
On 6 April 2022, a Boeing 767-300 lost left engine oil pressure whilst eastbound and passing south of Cork, Ireland. The aircraft diverted to Shannon after declaring an emergency due to intended engine shutdown. During the subsequent taxi in, a brake fire was observed and extinguished. The aircraft was towed to the terminal after an initial fire service request for evacuation had been withdrawn. An engine oil leak from a chip detector, which had been routinely inspected by a company engineer prior to departure but not reinstalled correctly, was found to have caused the leak and thus the loss of oil pressure.
On 25 October 2021, a Boeing 737-800 had just reached its cruise altitude after takeoff from Perth, Australia, when a fuel imbalance message was displayed. Despite specified indications for a fuel leak as the cause of this message not being met, it was determined that the left engine should be shut down. A ‘PAN’ was declared and a diversion to Kalgoorlie completed. Inspection there found the fuel imbalance was within normal limits and that crew diagnosis of a fuel leak had been flawed. Non-standard closure of the crossfeed valve was suspected as the origin of the imbalance.
Destination diversion
On 17 October 2022, an Airbus A320neo was unable to even make an approach at either its intended destination of Riohacha or its designated alternate after those airports were both closed because of adverse convective weather which developed over a significant part of Northern Columbia. A MAYDAY was declared due to low fuel and only 282 kg remained after the eventual landing at Santa Marta. Decision making by both the aircraft Operator and the flight crew involved and a lack of reliable communication between them was deemed contributory to what came very close indeed to being a hull loss accident.
On 12 August 2024, an ATR 72-500 making a Category 1 ILS approach to Guernsey with thick fog breached the applicable Approach Ban by continuing its descent below the applicable minimum altitude of 1,000 feet agl and then continued below what would have been the applicable 200 feet agl Decision Altitude without any visual reference. At around 70 feet agl, a go around was called but not correctly commenced and the aircraft passed close to an unseen mast north of the runway before it eventually climbed. In the absence of any visibility improvement, a diversion to Southampton then followed.
On 17 January 2023, an ATR 72-200 in the final stages of a CAT 2 ILS night approach to East Midlands experienced an electrical malfunction which disabled one set of primary flight instruments and triggered multiple system status indication failures. These included false system warnings and radio communications problems. The approach was discontinued, a MAYDAY declared and a successful manually flown diversion to Birmingham was made. The cause of the electrical malfunction was found to be a wiring defect, which was considered to have probably been caused by incorrect use of mechanical wire-stripping tools during third party maintenance.
On 21 December 2023, a Boeing 737-800 experienced a flap load protection response to turbulence during a night go-around at Billund, which locked the flaps in a mid-range position. A diversion to Copenhagen was commenced, but when it became clear that the fault would result in landing with slightly below minimum reserve fuel, a MAYDAY was declared. The flight was completed without further event. It was concluded that flap system locking had probably resulted from the crew’s manual selection of 15° flap just as the flap load relief system was responding, as designed, to a turbulence-caused flap overspeed condition.
On 16 September 2019, an ATR 72-200 diverted to Itaituba, Brazil, when landing at its intended destination of Manaus was prevented by the airport's unexpected closure due to an aircraft accident. During this diversion, intermittent indications of low fuel quantity were annunciated, and one engine subsequently ran down on final approach and the other whilst backtracking after landing. It was found that due to a series of undetected faults in the aircraft’s fuel quantity sensing system, the flight deck indications of fuel tank contents were over-reading and the low fuel indication system was also malfunctioning for the same reason.
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