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 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 only realised the landing altitude for their destination, Port Moresby, had not been set late in the descent. With insufficient time to eliminate the cabin pressure differential automatically, an attempt to use the abnormal manual control procedure was made. When it became clear that this had not worked, a go-around was initiated but 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 fortuitously 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 at night when sudden uncontained left engine failure occurred. Engine shutdown and initiation of a return was followed by consequential 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 still felt to be 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 eighteen 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.
On 20 February 2021, a Boeing 777-200 climbing through 12,500 feet experienced a sudden right engine failure and fire shortly after thrust had been increased before entering airspace where moderate turbulence was expected. Despite actioning the corresponding drills, the fire did not go out until shortly before landing back at Denver. Engine debris fell to the ground over a wide area, fortuitously with only damage and no injuries. The failure was found to have been initiated by the fatigue failure of a single fan blade after required routine inspections had failed to find early-stage evidence of such a risk.
En-route diversion
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 it was set to idle and shutdown after landing. On arrival at the assigned parking position, fuel was seen leaking from the right wing and a rapid passenger disembarkation was completed. Engine imbalance after turbine blade fracture was found to have caused the fuel leak and a risk of more potentially serious consequences after this scenario was identified.
On 6 April 2022, a Boeing 767-300 lost left engine oil pressure whilst eastbound and passing south of Cork and diverted to Shannon after declaring an emergency on account of intended engine shutdown. During the subsequent taxi in, a fire was observed and extinguished and the aircraft 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 when a fuel imbalance message was displayed on the system panel. 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.
On 17 January 2022, about 30 minutes after takeoff from Fort-de-France, Martinique, on an ETOPS flight, an Airbus A330-900 was approaching its initial cruise altitude when the apparently unconscious Captain appeared initially unresponsive. On being more aggressively roused, he seemed normal and a doctor on board initially assessed him as fit to continue. However, about two hours into the flight his condition subsequently deteriorated and the First Officer called the Chief Purser to take his seat to assist. A PAN, later upgraded to a MAYDAY, was declared and a diversion was made to Lajes where the Captain was hospitalised.
Destination diversion
On 17 January 2023, an ATR 72-200 in the final stages of a CAT 2 ILS night approach to East Midlands experienced a significant 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 then made. The cause of the electrical malfunction was found to be a wiring defect which was considered to have probably been caused by the 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 when landing at its intended destination Manaus was prevented by its 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.
On 31 January 2022, a Bombardier Challenger 604 pilot lost control during the final stages of a London Stansted night crosswind landing. A bounced nose-gear-first touchdown was followed by a brief runway excursion onto grass before a return to the runway and a climb away. A diversion to London Gatwick followed without further event but subsequent inspection revealed structural and other damage sufficient to result in the aircraft being declared an economic hull loss. The Stansted touchdown was found to have occurred after a premature flare at idle thrust continued towards the stall and a momentary stick pusher activation occurred.
On 25 October 2022, a Boeing 777-300ER encountered deteriorating weather conditions after initiating a delayed arrival diversion from Singapore Changi to nearby Batam where four approaches were flown and a ‘MAYDAY Fuel’ declared before a landing was achieved. By this time, the fuel remaining was “significantly below final reserve” although the actual figure was not published in the Investigation Report. It was concluded that the delay in commencing the diversion and the inappropriate attempt to perform an autoland on RWY04 at Batam airport by the flight crew contributed to the potentially hazardous circumstances.
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