8
$\begingroup$

I was watching this video of a FedEx MD-10 landing and some questions came up, of course again the unprofessional YouTube comments didn't help.

  • How many miles before the runway should an airliner put the gear down?
  • Was the aircraft in the video too close?
  • At which distance does radio altimeter warn the pilots?
  • Is the following YouTube comment accurate?

This was FedEx flight 1356 and I can tell you what happened. During approach there was an anomaly on the left slat and it was being watched. Also during approach engine no.1 was heating up to unacceptable levels and because of all of this the gear wasn't lowered right away. It was only due to TCAS and the alarms on board that it was noticed as the aircraft was approaching it's minimums. Upon landing the crew was reprimanded for not following proper procedure and was suspended with pay.

Improve this question
$\endgroup$
5
  • 7
    $\begingroup$ TCAS doesn't warn the pilots for gear up approach (incorrect landing configuration); it's the radio altimeter that does. $\endgroup$
    – ratchet freak
    Nov 17, 2014 at 16:05
  • 4
    $\begingroup$ Similar, if not duplicate: When do pilots deploy landing gear? $\endgroup$
    – Farhan ♦
    Nov 17, 2014 at 16:07
  • $\begingroup$ I'm not sure if this can be answered well. The general question about when to lower the gear has been answered already (see Farhan's comment); whether it was too close or not is speculation unless you know the aircraft's position and speed etc.; confirming whether or not Fedex disciplined the crew is difficult unless it was reported publicly, which is unlikely since the flight apparently landed safely; the question about the radar altimeter is good but kind of lost among the rest (this is one reason to ask only one thing per question). $\endgroup$
    – Pondlife
    Nov 17, 2014 at 16:58
  • 6
    $\begingroup$ It's not TCAS for the ground warning, it's the GPWS, Ground Proximity Warning System... or EGPWS, Enahanced GPWS. $\endgroup$
    – slookabill
    Nov 17, 2014 at 17:03
  • 1
    $\begingroup$ The quoted comment contradicts the video's description about the flight number (description says 309, not 1356) and doesn't know what TCAS is for. Seems unlikely that the rest would be correct. $\endgroup$
    – David Richerby
    Aug 3, 2017 at 20:25

2 Answers 2

Reset to default
13
$\begingroup$

To answer the last part of your question, as ratchet freak said, the TCAS doesn't warn the pilot when he should deploy landing gear. However, the ground proximity warning system/terrain avoidance and warning system (GPWS/TAWS) does. GPWS Mode 4A is "Unsafe Terrain Clearance With Landing Gear Not Down".

If the plane is less than 700ft (based on the radio altimeter's measure) high and under mach .35, there is an aural alert in the cockpit saying "Too low - gear". The message is repeated until the situation is corrected.

So the warning is based on the height and speed of the aircraft. Not on its distance to the airport.

Improve this answer
$\endgroup$
4
  • 3
    $\begingroup$ bonus points for saying 'height' and not 'altitude' $\endgroup$
    – rbp
    Nov 17, 2014 at 18:30
  • 2
    $\begingroup$ In cases where the airport is on top of a hill, would it also warn when you're below a certain height above the runway altitude or does it rely solely on the radio altimeter? For example, in the GA airport where I've done most of my flying, the runway sits on top of a ridge and there's a 400 foot drop very close to both ends of the runway. In such a case, would it potentially fail to warn you until you're almost right on the runway? $\endgroup$
    – reirab
    Nov 19, 2014 at 15:27
  • 5
    $\begingroup$ @reirab The enhanced GPWS (EGPWS) is also available with a GPS. In this case, it can be set up to warn the pilot based on a airport terrain database and the GPS position, as to prevent the kind of situation you describe. $\endgroup$
    – usernumber
    Nov 26, 2014 at 13:50
  • 1
    $\begingroup$ ...so if the plane is less than 700 feet AGL with gear up, but is travelling faster than Mach 0.35, they won't get that warning? $\endgroup$
    – Vikki
    Apr 27, 2018 at 17:51
2
$\begingroup$

As people have said I the comments there is no general rule as to when to lower the gear.

All major airlines have Standard Operating Procedures. As part of the Normal Procedures Section there will be profiles for the different types of approaches (ILS, GNSS, VOR etc..). It's normal as part of these to show the recommended config of the aircraft at a particular stage of the approach.

An example would be to lower the gear when capturing the Glide Path as part of an ILS approach. This aids speed control and ensures the aircraft is stable at the required minima.

Improve this answer
$\endgroup$
3
  • $\begingroup$ another good reason for putting the gear down at glide slope intercept is that it requires only one power change instead of two to stay on Vref (one power change intercept to begin the descent, and another power change when the gear is deployed). $\endgroup$
    – rbp
    Nov 17, 2014 at 18:33
  • 2
    $\begingroup$ Well, there is some rule. The already linked answer indicates the before landing checklist (which includes gear down) should be complete by 500 ft above field elevation in VMC and 1000 ft in IMC; in large planes that react more slowly it should generally be 1000 ft always. $\endgroup$
    – Jan Hudec
    Nov 18, 2014 at 8:00
  • $\begingroup$ As I stated it would depend on the operators procedures. Which is what the linked answer refers to. There is no "general" rule as it is operator and type specific. $\endgroup$
    – vectorVictor
    Nov 18, 2014 at 8:20

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .