Lufthansa B733 at Frankfurt on Sep 30th 2005, wake turbulence

Last Update: August 4, 2015 / 14:09:14 GMT/Zulu time

Bookmark this article

Photo of Lufthansa D-ABEA, Boeing 737-300 — Lufthansa D-ABEA, Boeing 737-300 (Photo credit: airlines470 / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Sep 30, 2005

Classification
Report

Airline
Lufthansa

Flight number
LH-4019

Departure
Turin, Italy

Destination
Frankfurt/Main, Germany

Aircraft Registration
D-ABEA

Aircraft Type
Boeing 737-300

ICAO Type Designator
B733

A Lufthansa Boeing 737-300, registration D-ABEA performing flight LH-4019 from Turin (Italy) to Frankfurt/Main (Germany) with 90 passengers and 5 crew, was on approach to Frankfurt's runway 25L at 2700 feet MSL about 10nm before touchdown, slightly below the glidepath.

A Boeing 747-400 was on approach to Frankfurt's runway 25R (which today is runway 25C after later opening of Frankfurt's fourth runway) about 5nm before touchdown.

About 9.8nm before touchdown the Boeing 737-300 encountered an uncommanded roll to the right reaching a bank angle of 23 degrees, the autopilot counteracted the roll, followed by a stronger uncommanded roll to the left, the autopilot was disengaged. The left bank angle reached 62 degrees and was manually counteracted. The crew positioned the aircraft slightly above glideslope and continued for a safe landing.

On Jul 10th 2015, almost 10 years after the occurrence, Germany's BFU released their factual report without conclusion reporting, that the Boeing 737-300 encountered wake turbulence from the Boeing 747-400.

Weather services reported that the winds at about 1000 meters/3300 feet were from 280 degrees at 10-12 knots.

Germany's Aeronautic and Space Centre's (DLR) Institute of Flight systems participated in the investigation and concluded the 737 had encountered wake turbulence. At the time of the autopilot disconnection the distance between the two aircraft was 4.6nm, at the time the wake turbulence had been generated, the B733 was still 6nm behind the B744.

Based on radar and flight data recorder data the B744 was at 3000 feet at 175 KIAS, gross weight was estimated at 278 tons. The DLR computed that the wake vortices were generated at a circulation of 490 m2/s based on the speed of the B744 at 90m/s. Using models of how wake turbulence would decay and move, as well as the flight data recorder showing the B744 was above glideslope at that point, the DLR produced models of how the wake vortices would evolve until the B733 overflew the area. The DLR computed that the wake vortices were still at a circulation of 380m2/s 99 seconds after they had been generated by the B744, when the B733 passed the area. The B737 passed the area about 48 meters/160 feet below the estimated wake and at a horizontal distance of 273 meters/900 feet.

The BFU wrote initially: "For a category Medium airplane this is strong wake turbulence if it is encountered in such short distance.", in an update on Aug 3rd 2015 the BFU changed to "For a category Medium airplane this is strong wake turbulence which can cause this particular reaction if encountered in relevant distance."

The BFU wrote, that the required minimum separation of a medium category aircraft (B733) to a preceeding heavy category aircraft (B744) was 5nm.

On Aug 3rd 2015 (and Aug 4th 2015 requesting an update into the quotation) a participant into the investigation contacted The Aviation Herald pointing out, that the BFU had updated the report and changed the sentence "For a category Medium airplane this is strong wake turbulence if it is encountered in such short distance". The participant told The Aviation Herald: "It is important to note that the distance between the B737 and the wake was only approximated based on available meteo data. An actual wake encounter with a wake and an aircraft reaction like this will only happen at a smaller distance! Nevertheless considering the overall situation and the wind uncertainties it can be assumed that this was a wake encounter."